Dissertations / Theses on the topic 'Strontium'

In the present thesis the relaxor properties of the tungsten-bronze ferroelectric material strontium-barium niobate Sr_1-wBa_wNb₂O₆ (SBN) are investigated. SBN is a very good experimental realization of the three-dimensional random-field Ising model (3d RFIM). The quenched random fields (RF) originate from charge disorder and can be enhanced by doping with Ce³⁺. They are responsible for the formation of polar nanoclusters in the paraelectric phase. In order to study the critical behavior of SBN, linear birefringence (LB) and second harmonic generation (SHG) have been measured as a function of temperature. Within an Ornstein-Zernike analysis of the LB data the autocorrelation function, <P²>, was determined, whereas the dipolar correlation length was obtained from the SHG data. They suggest that, due to its intrinsic disorder, pure SBN does not belong to the 3d Ising universality class. Doping with Ce³⁺ions, which seem to generate RFs, enhances the relaxor properties. The critical exponents v and y of SBN:Ce shift against those of the 3d RFIM. The domain morphology of SBN:Ce has been investigated by piezoelectric force microscopy (PFM). Fractal-like shaped zero-field cooled nanodomains are observed. Their size distribution can be described by a power law with exponential cutoff in accordance with prediction for the RFIM. It was measured for the first time in a RF system. The temperature and field induced evolution of natural and written domains has been studied with PFM, LB and SHG measurements. It reveals a very slow relaxation from a macrodomain into a depolarized multidomain state (and vice versa) even above T_C. This hints at strong pinning forces due to quenched RFs. They are also responsible for the observed aging in poled SBN and the field induced cluster percolation above T_C measured with SH-hysteresis. The domains can be considered as a "thick" phase grating for SH-diffraction. The Bragg-regime diffraction efficiency reflects the temperature and field induced change of the averaged domain sizes in the system.

The objective of this thesis is to construct a measurement system, measuring Radiation from Strontium with mass number 90 ( 90 Sr). The absorbed beta particle has a kinetic energy of 546 keV. The constructed scanning system makes it possible to sweep over a larger area than the actual Silicon detector. The used detector has an area of 1cm 2 . [1] A Si detector is connected to an electronic read out circuit. The Arduino microcontroller reads the output of the circuit and translates it to digital signals and sends them to a personal computer. After one signal has been read, Arduino will discharge the peak detector in the circuit to read another signal. The Arduino control software Processing will receive and process the digital output from Arduino. There will be three windows showing the number of counts from Arduino, the movement of the steering engine controlled by Thorlabs, and the sum counts of every position where the detector is.

The Melt-Leach-Evaporation (MLE) process is under development for the extraction of valuable Group IA or IIA metals of the Periodic Table, such as lithium, calcium, magnesium and strontium. The process consists of mixing and contacting the value metal source material, which might be an ore or concentrate, with an excess of molten metal which is acting as a reductant and lixiviant. In the process, the value metal extracted from the source material is dissolved in the excess molten metallic solvent and is subsequently extracted as a vapour by vacuum distillation. The vapour is condensed and recuperated in the metallic state.
An experimental program involving eight experiments was carried out. The experimental procedure consisted in essence of melting the aluminum reductant in a crucible and adding the source material, SrCO$ sb3,$ and other reactant (Mg or Bi). (Abstract shortened by UMI.)

Cold gases of Rydberg atoms are an ideal system in which to study the novel effects of strong interatomic interactions. This thesis describes the design and construction of the world's first experiment to study Rydberg states in a cold gas of an alkaline earth metal, in this particular case strontium. We have studied a wide range of Rydberg states, and have developed a sensitive ``step-scan" spectroscopic technique that detects the spontaneous ionization of the Rydberg gas. The step-scan method is used to acquire Stark maps, and these measurements verify a single-electron model for calculating dipole matrix-elements. From the matrix-elements, interaction strengths between strontium Rydberg atoms have been calculated for the first time. The presence of two valence electrons in an alkaline earth metal, such as strontium, offers a new angle on the study of Rydberg atoms. We create doubly excited ``autoionizing" states, the first such study in a cold gas. Autoionization is used as a high yield probe of Rydberg states, and enables a study of excitation dynamics with nanosecond time-resolution. We show that autoionization can quantitatively identify and elucidate state mixing in the Rydberg gas, and probe population transfer at the very onset of ultra-cold plasma formation.

In this thesis, a weak coupling formalism is developed to study superconductivity in spin-orbit coupled, multi-orbital systems. This formalism is then applied to Sr2RuO4, one of the few candidates for odd-parity superconductivity. We show that spin-orbit coupling and multi-band effects are crucial to understand the physics of this material. Depending on the interaction parameters, the order parameter can either be chiral or helical. In both cases, the gap is highly anisotropic, and has accidental deep minima along certain directions, in accordance with experiments. Focusing then on the chiral case, we show that the total Chern number is -7 instead of the usually assumed +1. This leads to drastically different predictions for the thermal and charge Hall conductances. In particular, we show that the absence of measurable charge edge currents is not incompatible with a chiral state. Finally, we study the evolution of superconductivity in Sr2RuO4 under ?100? uniaxial strain. We find a good agreement with experiments for our prediction of Tc as a function of strain. Furthermore, we find that (1) the absence of a measurable cusp of Tc at zero strain is not incompatible with a chiral state and that (2) there could be a transition to an even-parity state at larger strain close to a Van Hove singularity. We propose Hc,2/Tc2 c as a measurable quantity to identify this transition.

Aquesta Tesi estudia les propietats de Commutació Resistiva en capes primes de la sèrie de Ruddlensen-Popper de Iridats d’Estronci (Srn+1IrnO3n+1), posant el focus en els efectes de les transicions metall-aïllant d’aquestes fases en les característiques de la commutació resistiva. Amb l’objectiu d’assolir aquest propòsit, la deposició d’iridats mitjançant polvorització catòdica es estudiada. En el transcurs de la investigació, es va trobar que la polvorització catòdica, a diferència de la deposició per polsos de làser, presenta un creixement preferencial per al membre perovskita de la família (SrIrO3 amb desviacions de la estequiometria nominal. Aquest creixement esta controlat principalment per processos cinètics i posseeix un gran efecte de reemissió observat a altes temperatures. Una caracterització microestructural completa ens mostra que les capes obtingudes són planes, estables, homogènies i posseeixen un alt nivell de cristal·linitat. A més a més, les condicions de deposició d’aquestes capes van ser alterades per ajustar la morfologia de les capes des de topografies planes a nanoestructures amb forats, els quals poden ser ordenats d’acord amb el substrat. Amb l’objectiu de tenir un punt de comparació, capes de Sr2IrO4 han estat crescudes mitjançant deposició per polsos de làser. Després d’obtenir capes d’alta qualitat de les fases SrIrO3 i Sr2IrO4, les seves propietats elèctriques son avaluades. Per una banda, les capes de Sr2IrO4 van presentar un comportament aïllant, el qual reflecteix la seva naturalesa d’aïllant de Mott, per l’altre, el de les capes gruixudes de SrIrO3 van mostrar un estat base semimetàl·lic. Reduint el gruix en aquestes últimes una transició Metall-Aïllant pot ser desencadenada a baixes temperatures. Aquest règim, el qual exhibeix magnetoresistència negativa a baixes temperatures, està en consonància amb el mecanisme de localització dèbil en 2D, indicant el desordre com l’origen de la transició. Una reducció a gruixos més baixos porta el sistema a un canvi abrupte cap a un comportament totalment aïllant acompanyat per un increment significatiu de la magnetoresistència negativa i un desplaçament lleu en el balanç de portadors, el qual es mesurat per efecte Hall. Aquest comportament pot ser atribuït a una localització forta de Anderson. Les capes nanoestructurades també van presentar la mateixa transició però amb una evolució més suau de les propietats. Les mesures elèctriques locals realitzades amb Microscòpia de Força Atòmica de Corrent i Microscòpia de Sonda Kelvin van provar que ambdues fases posseeixen propietats robustes de commutació resistiva. Malgrat això, el estat base electrònic de cada capa té un impacte en les característiques de la commutació. Mentre que les capes semimetàl·liques de SrIrO3 van mostrar una transició suau entre estats de resistència, les capes ultraprimes aïllants van presentar un clar voltatge llindar a 2 V. Aquesta commutació més abrupta és replicada també per les capes aïllants de Sr2IrO4, que exhibeixen un llindar a 4,5 V. Un model de mecanisme basat en l’addició o subtracció de vacants d’oxigen en la interfície de les capes es proposat per explicar els resultats observats. Els canvis en el estat de resistència són atribuïts a desplaçaments en el nivell de Fermi dels materials. Per una banda, la continuïtat de estats electrònics en les capes semimetàl·liques causa una commutació suau. Per l’altre, la presencia de estats localitzats de Anderson o una separació energètica de Mott crea una barrera energètica que força el sistema a una commutació mes abrupta modelada per el voltatge llindar.
Esta Tesis estudia las propiedades de conmutación resistiva en capas delgadas de la serie de Ruddlensen-Popper de Iridatos de Estroncio (Srn+1IrnO3n+1), poniendo el foco en los efectos de las transiciones metal-aislante de estas fases en las características de la conmutación resistiva. Con el objetivo de alcanzar este propósito, la deposición de iridatos mediante la pulverización catódica es estudiada. En el transcurso de la investigación se encontró que la pulverización catódica, a diferencia de la deposición por pulsos de láser, presenta un crecimiento preferencial para el miembro perovskita de la familia con desviaciones en la estequiometría nominal. Este crecimiento está controlado principalmente por procesos cinéticos i posee un gran efecto de reemisión observado a altas temperaturas. Una caracterización microstructural completa nos muestra que las capas obtenidas son planas, estables, homogéneas y poseen un alto nivel de cristalinidad. Además, las condiciones de deposición de estas capas fueron alteradas para ajustar la morfología de las capas des de topografías planas a nanoestructuras con agujeros, los cuales pueden ser ordenados de acuerdo con el sustrato. Con el objetivo de tener un punto de comparación, capas de Sr2IrO4 han sido crecidas mediante deposición por pulsos de láser. Una vez obtenidas capas de alta calidad de las fases SrIrO3 y Sr2IrO4, sus propiedades eléctricas son evaluadas. Por una parte, las capas de Sr2IrO4 presentaron un comportamiento aislante, el cual refleja su naturaleza de aislante de Mott, por otra parte, las capas gruesas de SrIrO3 mostraron un estado base semimetálico. Reduciendo el grosor de estas últimas una transición Metal-Aislante puede ser desencadenada a bajas temperaturas. Este régimen, el cual exhibe magnetoresistencia negativa a bajas temperaturas, está en consonancia con el mecanismo de localización débil en 2D, indicando el desorden como el origen de la transición. Una reducción a grosores más bajos lleva el sistema a un cambio abrupto hacia un comportamiento totalmente aislante acompañado por un incremento significativo de la magnetoresistencia negativa i un desplazamiento leve en el balance de los portadores, el cual fue medido por efecto Hall. Este comportamiento puede ser atribuido a una localización fuerte de Anderson. Las capas nanoestructuradas también presentaron la misma transición pero con una evolución más suave de sus propiedades. Las medidas eléctricas locales realizadas con Microscopía de fuerza Atómica de corriente y la microscopía de sonda Kelvin probaron que ambas fases poseen propiedades robustas de conmutación resistiva. Sin embargo, el estado base electrónico de cada capa tiene un impacto en las características de la conmutación. Mientras que las capas semimetálicas de SrIrO3 mostraron una transiciónsuave entre los estados de resistencia, las capa ultradelgadas aislantes presentaron un voltaje umbral a 2 V. esta conmutación más abrupta es replicada también por las capas aislantes de Sr2IrO4, que exhibieron un lindar a 4,5 V. Un modelo de mecanismo basado en la adición y substracción de vacantes de oxígeno en la superficie de las capas es propuesto para explicar los resultados obtenidos. Los cambios de estado de resistencia son atribuidos a desplazamientos en el nivel de Fermi de los materiales. Por una parte, la continuidad de estados electrónicos en capas semimetálicas causa una conmutación suave. Por otra parte, la presencia de estados localizados de Anderson o una separación energética de Mott crea una barrera energética que fuerza al sistema a una conmutación más abrupta modelada por el voltaje umbral.
The present thesis studies the Resistive Switching properties in Ruddlensen-Popper strontium iridates (Srn+1IrnO3n+1) thin films, focusing on the effect of Metal-Insulator Transitions of these phases in the Resistive Switching features. In order to achieve this purpose, the deposition of iridates by sputtering is studied. During the course of the research it was found that the sputtering technique, unlike the more studied PLD, presents a preferential growth for the perovskite member of the family (SrIrO3) with deviations from the nominal stoichiometry. This growth is mainly controlled by kinetic processes with a large resputtering effect observed at high temperatures. A complete microstructural characterization has shown that the obtained films are flat, stable, homogeneous and possess a high level of crystallinity. Additionally, the conditions of deposition in these films were altered to tune the morphology of the film from flat to a nanostructured topography with holes that can be ordered according to the underlying substrate. For the sake of comparison, Sr2IrO4 films were grown by PLD. After obtaining high quality films of the SrIrO3 and Sr2IrO4 phases, their electrical properties are evaluated. While Sr2IrO4 films presented an insulating behavior, which reflects their Mott insulator nature, the thick perovskite SrIrO3 films showed a semimetallic ground state. As the thickness of the SrIrO3 film is reduced a Metal-Insulator Transition is triggered at low temperature. This regime, exhibiting negative magnetoresistance at low temperature, is in well agreement with the Weak localization mechanism in 2D indicating the disorder as the origin of the transition. Further lowering the thickness leads to an abrupt change of behavior to a fully insulating film that is accompanied by a significant increase of the negative magnetoresistance and a slight change in the balance between carriers as measured by Hall Effect. This behavior may be attributed to strong Anderson-like localization. The nanostructured films also presented the same transition but with a softer evolution of the properties. Local electric measurements performed with Conductive Atomic Force Microscopy and Kelvin Probe Force Microscopy proved that both studied phases possess robust bipolar Resistive Switching. Nevertheless, the electronic ground state of each film has a significant impact on the characteristics of this switching. While the thick semimetallic SrIrO3 films showed a smooth transition between resistance states, the insulating thinnest films presented a clear threshold at 2 V. This more abrupt switching is also replicated by the insulating Sr2IrO4 film, which exhibited a 4.5 V threshold. A mechanism model based in the addition or subtraction of oxygen vacancies in the interface of the films is proposed to explain the observed results. The changes in the resistance state are attributed to shifts in the Fermi level of the materials. On one hand, the continuum of electronic states in the semimetallic films causes a soft switching. On the other hand, the presence of Anderson localized states or a Mott band gap create an energy barrier that forces the system into a more abrupt switching shaped by a threshold.
Universitat Autònoma de Barcelona. Programa de Doctorat en Ciència de Materials

Strontium titanate (SrTi03) is a perovskite material with diverse physical properties. Many of its properties are associated with its atomic structure, such as quantum paraelectricity, structural phase transitions, and extrinsically induced ferroelectricity. Accordingly, many structural investigations have been performed on bulk and thin film samples of SrTi03 . At the same time, many syntheses of SrTi03 nanoparticles and nanowires have been reported. Despite these factors, however, the structure and properties of SrTi03 nanoparticles and nanowires are not well understood. The aim of this thesis is to better understand such SrTi03 nanoparticles and nanomaterials using a combination of theoretical and experimental methods. Density-functional calculations were performed of bulk SrTi03 and (100) SrTi03 surfaces, with a focus towards nanomaterials applications. The outer layers of both SrO and Ti02 terminated (100) surfaces relaxed inward, and the subsequent layers alternately moved outwards and inwards. Furthermore, surface rumpling was observed. Both the interlayer distances and rumpling were determined as a function of depth. Tests of different exchange-correlation functionals were performed throughout. Next, the first-ever density-functional calculations were performed of the structural and electronic properties of SrTi03 nanowires. No ferroelectric states were found for the nanowires, despite active searching. Compressive axial and lateral strain was observed for all the nanowires, and the extent of this strain varied with diameter and surface termination. Furthermore, surface rumpling was found to occur on and within the nanowires; subsequent plots of the local polarization revealed that every nanowire possessed a radial polarization texture. Finally, electronic band structure calculations revealed that all the SrTi03 nanowires were metallic. Finally, experimental studies were performed on SrTi03 nanoparticles, with the longterm aim of determining and understanding their local atomic structure. Transmission electron microscopy showed that the nanoparticles were polydisperse, and powder x-ray diffraction measurements showed that they were composed of mostly SrTi03.

Approximately 80% of Virginians with private drinking water (PDW) sources are unaware of the quality of their drinking water. Strontium is a water quality contaminant gaining recognition at the federal level. At concentrations >1.5 mg/L, strontium substitutes calcium in the bones leading to bone density disorders (e.g. rickets). This is particularly problematic for children and individuals with low calcium and low protein diets. Because most Virginians do not know the quality of their PDW and since strontium poses a public health risk, this study investigates the sources of strontium in PDW in Virginia and identifies the areas and populations most vulnerable. Physical factors such as rock type, rock age, and fertilizer use have been linked to elevated strontium concentrations in drinking water. Meanwhile, social factors such as poverty, poor diet, and adolescence also increase social vulnerability to health impacts of strontium. Thus, this study identifies both physically and socially vulnerable regions in Virginia using water quality data from the Virginia Household Water Quality Program and statistical and spatial analyses conducted in RStudio 1.0.153 and ArcMap 10.5.1. Physical vulnerabilities were highest in the Ridge and Valley province where geologic formations with high strontium concentrations (e.g., limestone, dolomite, sandstone, and shale) are the dominant the aquifer rocks. The complex relationship between agricultural land use and strontium concentrations made it difficult to determine the impact of fertilizer use on strontium concentrations in PDW in Virginia. In general, the spatial distribution of social vulnerability factors was distinct from physical factors with the exception of food deserts. This study provides information and analysis to help residents of Virginia understand their risk of strontium exposure in PDW.
Master of Science
There are 1.7 million residents in Virginia that rely on private drinking water supplies in their homes. Those individuals are responsible for knowing how often to test their water, what to test their water for, and how to treat their water, if needed, to achieve safe drinking standards. Unfortunately, approximately 80% of Virginians with private drinking water sources (e.g., wells, cisterns, and springs) do not know if their water is safe to drink. Strontium, an element closely related to calcium, is a contaminant that the federal government recognizes as dangerous because in high quantities (>1.5 mg/L of water) it can replace calcium in bones making them brittle (e.g. rickets). These health impacts are more extreme in children and individuals with low calcium and low protein diets. Since strontium poses a public health risk, this study identified areas and populations in Virginia that have higher chances of being exposed to strontium and higher chances of their health being impacted by high levels of strontium. Physical factors such as rock type, rock age, and fertilizer use have been linked to elevated strontium concentrations in drinking water, indicating various physical vulnerabilities. Meanwhile, social factors such as poverty, poor diet, and adolescence also increase social vulnerability to the health impacts of strontium. This paper investigates regions in Virginia that are likely to contain high strontium levels and thus potential health impacts from strontium. Statistical and spatial analyses of water quality data from Virginia Cooperative Extension’s Virginia Household Water Quality Program combined with risk factor data identified vulnerable areas in Virginia. The highest chance of exposure was in counties near the western border of the state (e.g., Augusta, Fredrick, Highland, Montgomery, Shenandoah, and Wythe) due to the presence of limestone, dolomite, sandstone, and shale, all of which naturally contain high amounts of strontium. The land use data indicated that there were no strong patterns of strontium occurrence relative to fertilizer use. In general, the spatial distribution of social vulnerability factors was distinct from physical factors with the exception of food deserts occurring at high rates in the same areas as the samples with high strontium levels (e.g., Augusta, Fredrick, Highland, Montgomery, Shenandoah, and Wythe). The presence of food deserts prevents individuals from obtaining a high calcium and high protein diet, which makes them more vulnerable to the impacts of strontium. Overall, this study can help people in Virginia who are not on public water systems understand their risk of from being exposed to strontium.

Les reconstitutions passées de la composition isotopique en Sr (87Sr/86Sr) des squelettes carbonatés d'organismes marins (MCS) sont très largement utilisées par les chimiostratigraphes et les paléoenvironnementalistes car elles permettent de reconstituer les variations du rapport 87Sr/86Sr de l'océan au cours des temps géologiques. Les reconstitutions paléoenvironnementales et les datations chimiostratigraphiques reposent sur le consensus que les MCS précipitent leurs tests carbonatés à l'équilibre isotopique avec l'eau de mer qui est homogène à l'échelle globale en raison d'un temps de résidence du Sr (2 Ma) supérieur au temps de brassage océanique (1600 ans). Leur fiabilité en tant qu'outils chimiostratigraphiques peut être remise en question, notamment parce qu'aucune évaluation formelle des biais biologiques et environnementaux n'a été réalisée à l'échelle mondiale. Cette étude propose donc une réévaluation à l'échelle globale de la signature isotopique en Sr des MCS et de l'eau de mer d'environnements côtiers. La signature isotopique des MCS et de l'eau côtière est largement influencée par des apports continentaux qui peuvent modifier les signatures isotopiques de ces derniers. De fait, au vu de ces hétérogénéités cette étude a recalculé le temps de résidence du Sr à plusieurs échelles spatiales. Elle propose de façon générale une meilleure compréhension des processus côtiers sur la signature isotopiques de l'eau et des MCS
Past reconstructions of the isotopic Sr composition (87Sr / 86Sr) of marine carbonate skeletons (MCS) are very widely used by chemostratigraphs and palaeoenvironmentalists because they allow to reconstruct variations of the 87Sr/86Sr ratio of the ocean across geological time. Paleoenvironmental reconstructions and chemostratigraphic dating are based on the consensus that MCS precipitate their carbonate skeletons at the isotopic equilibrium with surrounded seawater, that is considered as homogeneous at global scale due to a residence time of Sr (2 Ma) higher than the global ocean mixing duration(1600 years). Their reliability as chemostratigraphic tools can therefore be questioned, in particular because no formal evaluation of biological and environmental biases has been carried out at a global scale. This study proposes a global reassessment of the Sr isotopic composition of both MCS and seawater of coastal and oligotrophic environments. The isotopic signature of MCS and coastal water is largely influenced by continental inputs that can modify their isotopic signatures. In fact, given these heterogeneities, this study has recalculated the Sr residence time. Finally, this study propose a better understanding of the global strontium cycle at different time scale

First order trends in the strontium isotopic (87Sr/86Sr) composition of seawater are controlled by radiogenic inputs from the continent and non-radiogenic inputs from exchange at mid-ocean ridges. Carbonates precipitated in seawater preserve trace amounts of strontium that record this isotope ratio and therefore record the relative importance of mid-ocean ridge and weathering chemical inputs to sea water composition. It has been proposed that environmental changes during the Ediacaran-Cambrian transition may have enabled the rapid diversification of life commonly named the “Cambrian explosion.” Proposed environmental changes include 2.5x increase in mid-ocean ridge spreading at the Ediacaran-Cambrian boundary and large continental fluxes sediment into oceans. These hypotheses rely on a poorly resolved strontium isotope curve to interpret Ediacran-Cambrian seawater chemistry. A refined strontium isotope curve through this time period may offer insight into the environmental conditions of the early Cambrian. New age models and detailed mapping in the Zavkhan terrane in west-central Mongolia provide the context necessary for robust geochemical analysis. This study aims to better resolve the coarse strontium isotope curve for the early Cambrian period by analyzing carbonate sequences in the Zavkhan basin. These carbonate sections are rapidly deposited, have undergone little diagenesis, and are likely to preserve a primary seawater signal. Strontium isotope analysis of these sequences was carried out to determine changes in hydrothermal activity and weathering fluxes during this time period. Recompiling these data with a global dataset of strontium isotopes through this time period indicates a stable strontium isotope signal through much of the early Cambrian. These data do not support previous hypotheses attributing the driving mechanism for the early Cambrian transition from Mg-dominated to Ca-dominated seas to increased sea floor spreading rates.

ABSTRACT EXCHANGES OF STRONTIUM ON CLINOPTILOLITE ZEOLITE GÜ
L, Ö
zkan MS, Department of Chemical Engineering Supervisor: Prof. Dr. Hayrettin Yü
cel November 2003, 110 Pages Sr-90 and Cs-137, nuclear fission products, are the major sources of medium-level radioactive waste which must be decontaminated. Inorganic ion exchangers are the preferred materials to eliminate radioisotopes from aqueous nuclear waste because of their high selectivity, radiation and thermal stability, low cost and likely compatibility with cement containment. Clinoptilolite and other zeolites are widely used in nuclear industry for the removal of radioisotopes from aqueous nuclear waste. In this study, the performance of local clinoptilolite zeolite from Gö
rdes region has been investigated so as to determine the conditions under which it can be used effectively in the column for strontium and cesium removal. It was found that under different loading conditions, breakthrough capacity varied from 0 to 0.4078 meq/g for strontium removal, breakthrough capacity varied from 0.1178 to 0.7800 meq/g for cesium removal. It was also determined that the increase of the flow rate reduced the exchange capacity of the bed. Effect of cationic form of the zeolite (Na-CLI: Sodium form of clinoptilolite and Original-CLI: Original form of clinoptilolite) on the breakthrough capacity was also searched. It was observed that Na-CLI performed much better for the removal of strontium and cesium with respect to its original form. In addition, effect of presence of calcium in the feed solution on the breakthrough capacity was investigated and it was found that presence of calcium in the feed solution makes strontium removal essentially impossible, in the case of cesium, presence of calcium in the feed solution decreases breakthrough capacity significantly.

Magnesium is a low density metal that is an attractive alternative to steel and aluminum for weight reduction in automotive design. Automotive applications of Mg have steadily grown since the early 1990s. Limited deformation mechanisms at moderate temperatures and resulting poor formability have been the major limitations to the development of Mg wrought alloys. Specialized alloys with improved deformation behaviour exist for aerospace applications, however these are based on expensive alloy systems containing silver and rare-earth (RE) elements such as yttrium and neodymium. Effective use in high volume applications such as automotive components requires a more cost effective solution.Conventional low cost extrusion alloys based on the Mg-Al-Zn and Mg-Zn-Zr systems offer a solution however, they suffer from major problems of extrudability and poor formability. Strontium (Sr) has been introduced to replace RE additions in Mg alloys with an alkali-earth element. Sr has been used as an effective alloying element for grain and second phase refinement as it precipitates as intermetallic phases with high thermal stability. A fw studies have been conducted on the behaviour of these Sr-containing thermally stable precipitates during high temperature deformation. The primary objectives of this research were to study the microstructure, mechanical properties and texture evolution of AZ31 alloy containing various levels of Sr during hot deformation. In the first part of this study, the precipitation and solidification of AZ31-Sr castings was studied by thermal analysis and numerical modeling as a background to understand the formation of secondary phases and microstructural development. This was achieved by casting AZ31 alloys containing various levels of Sr, recording the cooling curves and comparing the findings with computer simulated generated using FactSage (thermodynamic calculation software). In the second part of this study the recrystallization and texture evolution during hot bar extrusion of AZ31-Sr alloys in three sections is characterized. In the first section (3.1) it was shown that Particle-Stimulated Nucleation (PSN) occurred in the deformed regions around the precipitates in certain hot working conditions at 350oC. Increasing the amount of Al-Sr stringers in AZ31 increased the potential sites for PSN. In the following two chapters, the yield asymmetry of AZ31-Sr extruded bars (section 5.1) and the effect of annealing before hot extrusion (section 6.1) were examined. The tensile and compressive strengths of extruded AZ31 alloys containing different levels of Sr depended more on the extrusion temperature than on the Sr concentration and also the yield asymmetry of the AZ31+xSr alloys increased with increasing extrusion temperature. However, the increase was less when Sr was present in the alloy. Section 6 reports results obtained from AZ31+0.8Sr subjected to annealing prior to extrusion at four different times. An increase in the duration of the pre-deformation anneal switched the plane facing the extrusion direction from first order prismatic (100) to second order prismatic planes (110). In the final of part of this thesis, the microstructures and textures of hot extruded AZ31-Sr tubes were examined. Section 7.1 reports on seamed tubes that were extruded using a porthole die. The complex strain path inside the die could be divided into several simple curvatures which occur during ECAP (Equal Channel Angular Pressing). In section 7.2 the expansion behaviour of seamless AZ31-Sr tubes was studied by compressing the tubes with pure-copper cylinder-inserts. The texture of the extruded tube is comprised of two components: hoop direction (HD) and radial direction (RD), which behave differently during expansion. The HD component undergoes extension twinning while the contraction and double twinning occurs in RD grains.
Le magnésium est un métal de faible densité qui est une alternative intéressante à l'acier et l'aluminium pour réduire le poids dans la conception automobile. Les applications automobiles de Mg n'ont cessé de croître depuis les années 1990. Mécanismes de déformation limitée à des températures modérées et résultant formabilité pauvres ont été les principales limites à l'élaboration des alliages de Mg forgé. Alliages spécialisés avec le comportement de déformation améliorée existent pour les applications aérospatiales, mais ceux-ci sont basées sur les systèmes d'alliage contenant de l'argent et coûteux de terre rare (RE) des éléments tels que l'yttrium et le néodyme. L'utilisation efficace dans les applications à volume élevé tels que les composants automobiles nécessite une solution plus rentable.Classiques à faible alliages d'extrusion coûts basés sur le Mg-Al-Zn et Mg-Zn-Zr systèmes offrent une solution cependant, ils souffrent de problèmes majeurs de extrudabilité et la formabilité des pauvres. Strontium (Sr) a été introduit pour remplacer les ajouts RE alliages de magnésium avec un élément alcalino-terreux. Sr a été utilisé comme élément d'alliage efficace pour le grain et le raffinement deuxième phase car il précipite sous forme de phases intermétalliques avec une grande stabilité thermique. Quelques études fw ont été menées sur le comportement de ces Sr contenant thermiquement stable précipités lors de la déformation à haute température. Les principaux objectifs de cette recherche était d'étudier la microstructure, propriétés mécaniques et évolution de la texture de la AZ31 alliage contenant différents niveaux de Sr lors de la déformation à chaud.Dans la première partie de cette étude, la précipitation et la solidification de AZ31-Sr moulages a été étudié par analyse thermique et la modélisation numérique comme toile de fond pour comprendre la formation de phases secondaires et le développement de la microstructure. Ceci a été réalisé par coulée AZ31 alliages contenant différents niveaux de Sr, l'enregistrement des courbes de refroidissement et en comparant les résultats avec simulé par ordinateur générées en utilisant FactSage.Dans la deuxième partie de cette étude, la recristallisation et évolution de la texture lors de l'extrusion à chaud de barre de AZ31-Sr alliages en trois sections est caractérisée. Dans la première section (3.1), il a été montré que des particules stimulée par nucléation a eu lieu dans les régions déformées à travers le précipite dans certaines conditions de travail chaudes à 350C.Dans les deux chapitres suivants, le rendement de l'asymétrie AZ31-Sr barres extrudées et l'effet du recuit avant l'extrusion à chaud ont été examinés. Les forces de traction et de compression de extrudés AZ31 alliages contenant différents niveaux de Sr dépendait plus de la température d'extrusion que sur la concentration en Sr et aussi le rendement de l'asymétrie AZ31 + alliages XSR augmente avec la température d'extrusion augmente. Toutefois, l'augmentation était inférieure lorsque Sr était présent dans l'alliage. Section 6 résultats des rapports obtenus à partir AZ31 0,8 Sr soumis à un recuit avant l'extrusion à quatre moments différents. Lors de la finale d'une partie de cette thèse, les microstructures et les textures de chaudes extrudés AZ31-Sr tubes ont été examinés. Section 7.1 des rapports sur les tubes qui ont été cousus extrudé en utilisant une matrice hublot. Le chemin de déformation complexe à l'intérieur de la filière pourrait être divisé en plusieurs courbures simples qui se produisent pendant l'ECAP. Dans la section 7.2 le comportement d'expansion sans soudure AZ31-Sr tubes a été étudiée par la compression des tubes avec pur-cylindre de cuivre-inserts. La texture du tube extrudé est constitué de deux composantes: la direction cerceau et la direction radiale La composante HD subit de jumelage d'extension tandis que le jumelage de contraction et double se présente en grains RD.

Optical atomic clocks with precisions and accuracies in the 10\(^-\)\(^1\)\(^8\) level [1] are now the most advanced man-made timekeeping devices. They outperform the microwave cesium atomic clocks that realize the SI definition of the second. Scaling down the size of optical atomic clocks may open the door to a range of industrial and space applications. In this thesis, the design and preliminary results of a compact strontium cooling system are presented. In the first cooling stage, the high power 461 nm laser with 300 mW output features a modular design, while smaller laser sources for demonstrating a strontium magneto-optical trap have also been investigated. An innovative design that couples a spectroscopy cell directly into the scientific chamber reduces the overall size and power consumption of the system. Additionally, using strontium oxide as a source of strontium atoms suitable for optical clocks has achieved initial success. For the first time, a single-beam MOT configuration is applied to strontium. In this novel apparatus, the blue MOT and red MOT broadband cooling phases are able to trap 5x10\(^6\) and 1000 atoms, respectively. This work shows promising progress towards developing a functional miniaturized strontium optical lattice clock.

Previous structural work has shown that strontium undergoes a sequence of phase transitions up to 46 GPa. The relatively complex structures of Sr-IV and Sr-V, stable above 35 GPa and 46 GPa respectively, could not be solved and doubts remained about the correct assignment of the Sr-III structure. It is only comparatively recently, however, that experimental techniques have been developed to allow the detailed structural characterisation of these phases. To resolve these remaining uncertainties, the author has carried out a re-examination of the high-pressure structures and transitions in strontium using angle-dispersive powder-diffraction techniques with the image-phase area detector on station 9.1 at the SRS Daresbury Laboratory. The experimental set up has been improved so that data of sufficient quality could be obtained to allow the structures of these high pressure phases to be both correctly identified and accurately refined. The previously reported structure of Sr-III was found to be wrongly identified as having an orthorhombic Imma symmetry (with a structure similar to that of Si-III) and this has now been correctly identified as having the archetypal b-tin (I4₁ /amd) structure. The higher pressure phase of Sr, Sr-IV, has also been solved and the structure solution showed that it has a very complex monoclinic structure. This is the first time that this complex monoclinic structure has been reported in an element. Finally, the crystal structure of Sr-V has also been closely studied in comparison with the recently reported Ba-IV structure - based on the similarity of the diffraction patterns observed. The Sr-V structure is indeed found to be essentially the same as that of Ba-IV and it also has an intra-phase structural transition similar to those observed in Ba-IV.

Due to the recent success, in terms of accuracy and precision, of a number of strontium optical lattice optical frequency standards, and the classification of the 5s^{2 1}S₀ to 5s5p ³P₀ transition in neutral strontium as a secondary definition of the SI unit of the second, many new strontium lattice clocks are under development. The strontium optical lattice clock (Sr OLC) at the National Physical Laboratory (NPL) is one such project. This thesis describes the design and build of the NPL Sr OLC, discussing the considerations behind the design. Details of the first cooling stage are given, which includes the characterisation of a novel permanent-magnet Zeeman slower by measurements of the longitudinal velocity distributions and loading of the MOT at 461 nm. Development of a narrow linewidth laser system at 689 nm is described, which is used for initial spectroscopy of the second-stage cooling transition. In particular, this work describes progress towards two independent ultra-narrow linewidth clock lasers. The new generation of strontium lattice clock experiments have focused on characterising the systematic frequency shifts and reducing their associated fractional frequency uncertainties, as well as reducing the fractional frequency instability of the measurement. One focus of the Sr OLC at NPL is to help characterise the frequency shift of the clock transition due to black-body radiation (BBR), which is currently the largest contributor to the uncertainty budget of the measured clock frequency. Our approach, discussed here, is to make a direct, differential measurement of the shift with the atoms housed alternately in environments of differing temperatures. Better characterisation and control of the BBR frequency shift of the strontium clock transition is crucial for the future of the Sr OLC as a leading frequency standard.

Low temperature sintering has become a very important research area in ceramics processing and sintering as a promising process to obtain grain size below 100nm. For electronic ceramics, low temperature sintering is particularly difficult, because not only the required microstructure but also the desired electronic properties should be obtained. In this dissertation, the effect of liquid sintering aids and particle size (micrometer and nanometer) on sintering temperature and Positive Temperature Coefficient Resistivity (PTCR) property are investigated for Ba1-xSrxTiO3 (BST) doped with 0.2-0.3mol% Sb3+ (x = 0.1,0.2,0.3,0.4 and 0.5). Different sintering aids with low melting point are used as sintering aids to decrease the sintering temperature for micrometer size BST particles. Micrometer size and nanometer size Ba1-xSrxTiO3 (BST) particles are used to demonstrate the particle size effect on the sintering temperature for semiconducting BST. To reduce the sintering temperature, three processes are developed, i.e. 1 using sol-gel nanometer size Sb3+ doped powders with a sintering aid; 2 using micrometer size powders plus a sintering aid; and 3 using nanometer size Sb3+ doped powders with sintering aids. Grain size effect on PTCR characteristics is investigated through comparison between micrometer size powder sintered pellets and nanometer size powder sintered pellets. The former has lower resistivity at temperatures below the Curie temperature (Tc) and high resistivity at temperatures above the Curie temperature (Tc) along with higher ñmax/ñmin ratio (ñmax is the highest resistivity at temperatures above Tc, ñmin is the lowest resistivity at temperatures below Tc), whereas the latter has both higher ñmax and ñmin. Also, ñmax/ñmin is smaller than that of pellets with larger grain size. The reason is that the solid with small grain size has more grain boundaries than the solid with large grain size. The contribution z at room temperature and high temperature and a lower ñmax/ñmin ratio value.

The sudden onset of ground state deformation and the emergence of shape-coexisting states in the vicinity of N~60 and Z~40 has been a subject of substantial interest for many years. It has been shown that the emergence of deformed low-energy configurations can be explained in the shell model by the evolution of single particle structure and the interaction between protons and neutrons in certain valence orbitals. However, the numerous theoretical models that have been developed for this transitional region are limited by the experimental data that is available. In particular, a description of the underlying single particle configurations of low energy states is essential for a detailed description of this region. In this work, the single particle structure of states in ⁹⁵Sr and ⁹⁶Sr has been investigated through the one-neutron transfer reactions ⁹⁵ ⁹⁶Sr(d,p) in inverse kinematics at TRIUMF. In each of these experiments, a 5.5 MeV/u Sr beam was impinged on a 5.0 mg/cm² CD₂ target, and emitted particles and γ-rays were detected using the SHARC and TIGRESS detector arrays, respectively. Using an angular distribution analysis, firm spin assignments have been made for the first time of the low-lying 352 keV, 556 keV and 681 keV excited states in ⁹⁵Sr from ⁹⁴Sr(d,p), and a constraint has been made on the spin of the higher-lying 1666 keV excited state in ⁹⁵Sr. Similarly, angular distributions have been extracted for 14 states in 96Sr from ⁹⁵Sr(d,p), and new experimental constraints have been assigned to the spins and parities of 8 states in ⁹⁶Sr. Additionally, two new states in ⁹⁶Sr have been identified in this work. A measurement of the mixing strength between the 1229 keV and 1465 keV shape-coexisting states in ⁹⁶Sr was also made, which was found to be a²=0.48(17).
Science, Faculty of
Physics and Astronomy, Department of
Graduate

Strontium optical lattice clocks can measure the passage of time with extraordinary precision. Capitalising on this precision, we can anticipate the deployment of lattice clocks to search for new physics beyond the standard model, to build new technologies for geodesy and navigation, and potentially to underpin a future redenition of the SI second. This thesis reports on the construction and evaluation of a robust Sr optical lattice clock at NPL. We describe the apparatus needed to capture, cool, and load samples of neutral strontium atoms into a magic-wavelength, far off-resonant lattice trap at 813 nm. We provide details of our optical local oscillator - the "clock laser" - and how it is used to realise an Sr-referenced optical frequency standard. We rigorously characterise the various contributing factors which limit the performance of the clock, focusing on the standard measures of (1) frequency instability, and (2) systematic frequency uncertainty. Finally, we introduce new innovations for improving the accuracy of the 88Sr lattice clock, including methods of "modified hyper-Ramsey" and multi-photon spectroscopy of the clock transition.

Strontium titanate is a material of considerable interest, with many applications. Though it has been extensively studied experimentally and computationally, there are unresolved issues regarding the structure and defect properties. Experimental examination is challenging due to the propensity of the material to form small domains. Even when single crystals are available, the observed behaviour is an average of these local domains. In this thesis we undertook an extensive computational investigation of strontium titanate. The material is known to undergo a second order phase transition from cubic (Pm-3m) to tetragonal (I4/mcm) at ~105 K. We began the investigation by examining the tetragonal phase. Using plane-wave DFT with the LDA, PBE and PBEsol density functionals, we mapped out in three dimensions the I4/mcm space group and fitted the resultant potential energy surfaces to polynomials. Extensive analysis was performed and expectation values for the 0 K octahedral rotation angle were calculated as being between 4.6° and 6.1° for the three functionals. We continued by carrying out an extensive study, where we examined many different low symmetry saddle points, and minima using the PBEsol functional (which was found to have produced the best results). A total of 38 structures (many of which are unique) were examined in detail and the vibrational and imaginary modes involved in the transitions between higher and lower symmetry structures were identified and described. We identified the lowest energy structure as being monoclinic, with a rhombohedral structure at slightly higher energy. We also note that, as the energy differences are so small between these lower symmetry structures (~0.1 meV per formula unit), it is unlikely that these phases will appear in nature. In the final results chapter we present three new sets of classical pair potentials for modelling strontium titanate. We applied these potentials to model vacancy type defects and investigated the transition pathway for oxygen and strontium migration between adjacent sites. We calculated migration barriers of between 0.96 and 1.35 eV for oxygen and between 3.17 and 3.20 eV for strontium, which are improved estimates over previous pair potential results.

The growth of strontium sulfate precipitate by diffusion in various gels was studied by using optical transmission and confocal microscopies, scanning and transmission electron microscopies, and energy dispersive X ray fluorescence. Pure silica gel, pure agarose gel and the silica/agarose mixed gel at pH 7 - 10 were used throughout the present study. Precipitate morphology is sensitive to pH and to the nature of the growth medium. The morphology was observed as a function of time. The lack of change is presumably because of rapid depletion of the limiting reagent after the very beginning of precipitation. The problem of separating strontium sulfate precipitate from the gel medium is discussed.

Thermal loading models have been developed in order to predict the optimum input powers of free-convection cooled strontium recombination lasers (SRLs) and forced-convection cooled SRLs. Gas temperature models have also been developed for circular bore and rectangular bore SRLs, to complement the thermal loading models, so that the performances of circular and rectangular bore SRLs can be compared. It has been shown, in theory, that rectangular bore tubes offer operation at lower gas temperatures than do circular bore tubes of the same cross-sectional area, with the same input power per unit length. Laser performance is, therefore, expected to be improved through the use of rectangular bores in the construction of SRLs. The results of the thermal loading models are validated by experiments. The need to oven process alumina tubes in forming gas, prior to their use in the SRL, is demonstrated by an increase in output power from tubes processed using this technique. Enhanced radiative heat extraction, accompanied by an increase in average laser output power, is obtained from a free-convection cooled SRL by increasing the emissivity of the outer surface of the ceramic discharge tube. Three rectangular bore water-cooled SRLs, optimising at different input powers, have been constructed, operated and compared in performance to a free-convection cooled SRL, constructed using the same ceramic discharge tube. An average output power of 2.3 W has been obtained from a 40 cm long rectangular bore beryllia discharge tube through the use of active water cooling. This represents an improvement of over 200% when compared to the performance of a free-convection cooled SRL utilizing the same ceramic discharge tube.

I present the construction of a low-velocity intense source (LVIS) of laser-cooled neutral strontium using permanent ring magnets. The LVIS consists of a magneto-optical trap from which cold strontium is extracted in a well-collimated beam. I also present the development and implementation of a full suite of low-noise, high-bandwidth laser control electronics including a microcontroller unit. This microcontroller remotely controls and monitors the current driver, temperature controller, and PID lock circuit for each diode laser simultaneously. The current driver output is accurate to within 2 micro-amps and repeatable to with a few nano-amps. The noise spectral density of the current driver hits a floor of 10^(-10) amps per root Hz at ~50 Hz and has a modulation bandwidth of ~50 MHz. The PID lock-circuit includes a scan-balancing option that we have used to scan an AR coated laser diode ~30 GHz mode-hop free. I describe the construction of an 80 mW frequency doubled 461 nm laser system using PPKTP for cooling and trapping neutral strontium in the LVIS. The LVIS, the electronics systems, and the 461 nm laser system represent major milestones on the way to producing a matter-wave interferometer using Sr-87 ions. The interferometer is based on an optical Raman transition between the hyperfine ground states of the Sr-87 ion. The ions will be produced by exciting the strontium LVIS beam to an auto-ionizing state in the continuum. In the interferometer two half-pi pulses of light and one pi pulse will be delivered to the ions to split and recombine their wave functions. I present calculations of the predicted sensitivity and a discussion of the possible applications. I present a method for locking a 407.8 nm laser to the 5s doublet S J=1/2 to 5p doublet P J=3/2 strontium ion transition in a neutral vapor. I present calculations for the necessary vacuum levels for the experiment and describe the preparation and assembly of the vacuum apparatus. The major vacuum system consists of two connected elastomer sealed chambers: one at 10^(-7) Torr and the other at 10^(-10) Torr separated by a region of low conductance. I present a Sr vapor cell constructed from standard CF fittings that allows the strontium to be heated to ~730 C, which can also be run as a thermal beam. I present a method for protecting the viewports on small-form alkali-earth vapor cells using lead or indium foil during the evaporation of oxide layers. Finally, I report on the current status of the experiment as well as detail future work on the apparatus.

Thesis (MSc (Medical Physics))--University of Limpopo (Medunsa Campus),2010.
Key words: Monte Carlo simulation, MCNP5 code, Beta irradiation, Teflon-encased eye applicator, Dosimetry, Strontium-90 (Sr-90) Introduction: The treatment of various superficial lesions of the eye and skin has been conducted for many years, using Strontium-90 ophthalmic applicators. The dosimetry of the Sr-90 eye applicator is necessary, since it helps to determine a precise dose distribution within the eye globe. This also aids in optimizing the dose to be delivered to the target tissue of the eye without harming normal tissues, through surface dose rate determination. Thus, the surface dose rates are used to determine the lens and sclera dose, and also to specify the effectiveness of the applicator. These eye applicators are no longer manufactured and are commercially unavailable, because they have gone out of fashion. Those available are more than 20 years old. Due to recurrence in pterygium, glaucoma surgery enhancement and treatment of conjunctivae, the resurgence of the Sr-90 eye applicator is clinically needed. Hence, the Department of Medical Physics (University of Limpopo, MEDUNSA) proposed a new model of the Sr-90 ophthalmic applicator called the Teflon-encased eye applicator. Aim: To determine the radiation depth dose rate distributions of the Teflon-encased eye applicator, and to compare the calculated dose rates with that of the standard eye applicator (SIA. 8975) previously used and studied in MEDUNSA. Material and method: MCNP5 version 1.20 based Monte Carlo code was used. The first step involves verification of strontium-90 (Sr-90) and Yttrium-90 (Y-90) spectra. Second step, a new applicator model was designed. The third step, applicator was setup with water phantom, to determine dose distribution in water. Surface dose rate and central axis depth dose rate distributions were calculated. These were obtained in three different phases by varying the thickness of Teflon, different sources and changing the surface source distance (SSD) in order to determine their effects on central axis depth dose rates 2 and surface dose rates. The relationship of results was verified by correlation and ANOVA F- tests. Results and discussion: All spectra were demonstrated to be as reliable and accurate with relative errors ranging up to 7.9%, and correspond well to published available spectra. A Teflon thickness of 0.1 cm was sufficient to filter out and suppresses Sr-90 beta particles, and gave maximum beta penetration of 0.8 cm. No betas reached the back side of the applicator shaft. Only about 90% of the initial source dose escaped Teflonencased eye applicator. The surface dose rate increased exponentially with a decrease in Teflon thickness with regression coefficient of 97%. It also decreased linearly with increase in SSD and source thickness with a variation correlation of 99% and 99%, respectively. The source thicknesses of 0.03 cm, 0.04 cm, 0.045 cm and 0.05 cm gave closest results of 38.32 cGy/s ± 2.7%, 36.45 cGy/s ± 2.8%, 34.90 cGy/s ± 2.8% and 32.75 cGy/s ± 1.5% respectively, to the standard eye applicator having 36.55 cGy/s ± 2.5%. The depth dose results have a strong correlation and significance of 99%. An increased of Teflon thickness from 0.1 cm to 0.125 cm lead to a 27% decrease in central axis depth dose rate. All ten statistical checks from MCNP were passed with average relative error of ±3%, at one standard deviation. The accuracy of calculated central axis depth dose rates was within 5%. Conclusion: The central axis depth dose rate of the Teflon-encased eye applicator can only be calculated at a distance less than 0.5 cm depth of water, due to the applicator’s geometry. The geometry, materials, applicator shape, source size, and distance between source and phantom, input spectra and MCNP code used caused differences in results. However it was possible to minimise the differences. The surface dose rate can only be defined at a depth of 0.01 cm in a water phantom in order to accurately estimate the dose to lens and sclera. The dosimetry of the Teflon-encased eye applicator is similar to that of a standard eye applicator. Also, this newly modeled applicator is effective and it can be manufactured for clinical treatment purposes. Key words: Monte Carlo simulation, MCNP5 code, Beta irradiation, Teflon-encased eye applicator, Dosimetry, Strontium-90 (Sr-90) Introduction: The treatment of various superficial lesions of the eye and skin has been conducted for many years, using Strontium-90 ophthalmic applicators. The dosimetry of the Sr-90 eye applicator is necessary, since it helps to determine a precise dose distribution within the eye globe. This also aids in optimizing the dose to be delivered to the target tissue of the eye without harming normal tissues, through surface dose rate determination. Thus, the surface dose rates are used to determine the lens and sclera dose, and also to specify the effectiveness of the applicator. These eye applicators are no longer manufactured and are commercially unavailable, because they have gone out of fashion. Those available are more than 20 years old. Due to recurrence in pterygium, glaucoma surgery enhancement and treatment of conjunctivae, the resurgence of the Sr-90 eye applicator is clinically needed. Hence, the Department of Medical Physics (University of Limpopo, MEDUNSA) proposed a new model of the Sr-90 ophthalmic applicator called the Teflon-encased eye applicator. Aim: To determine the radiation depth dose rate distributions of the Teflon-encased eye applicator, and to compare the calculated dose rates with that of the standard eye applicator (SIA. 8975) previously used and studied in MEDUNSA. Material and method: MCNP5 version 1.20 based Monte Carlo code was used. The first step involves verification of strontium-90 (Sr-90) and Yttrium-90 (Y-90) spectra. Second step, a new applicator model was designed. The third step, applicator was setup with water phantom, to determine dose distribution in water. Surface dose rate and central axis depth dose rate distributions were calculated. These were obtained in three different phases by varying the thickness of Teflon, different sources and changing the surface source distance (SSD) in order to determine their effects on central axis depth dose rates 2 and surface dose rates. The relationship of results was verified by correlation and ANOVA F- tests. Results and discussion: All spectra were demonstrated to be as reliable and accurate with relative errors ranging up to 7.9%, and correspond well to published available spectra. A Teflon thickness of 0.1 cm was sufficient to filter out and suppresses Sr-90 beta particles, and gave maximum beta penetration of 0.8 cm. No betas reached the back side of the applicator shaft. Only about 90% of the initial source dose escaped Teflonencased eye applicator. The surface dose rate increased exponentially with a decrease in Teflon thickness with regression coefficient of 97%. It also decreased linearly with increase in SSD and source thickness with a variation correlation of 99% and 99%, respectively. The source thicknesses of 0.03 cm, 0.04 cm, 0.045 cm and 0.05 cm gave closest results of 38.32 cGy/s ± 2.7%, 36.45 cGy/s ± 2.8%, 34.90 cGy/s ± 2.8% and 32.75 cGy/s ± 1.5% respectively, to the standard eye applicator having 36.55 cGy/s ± 2.5%. The depth dose results have a strong correlation and significance of 99%. An increased of Teflon thickness from 0.1 cm to 0.125 cm lead to a 27% decrease in central axis depth dose rate. All ten statistical checks from MCNP were passed with average relative error of ±3%, at one standard deviation. The accuracy of calculated central axis depth dose rates was within 5%. Conclusion: The central axis depth dose rate of the Teflon-encased eye applicator can only be calculated at a distance less than 0.5 cm depth of water, due to the applicator’s geometry. The geometry, materials, applicator shape, source size, and distance between source and phantom, input spectra and MCNP code used caused differences in results. However it was possible to minimise the differences. The surface dose rate can only be defined at a depth of 0.01 cm in a water phantom in order to accurately estimate the dose to lens and sclera. The dosimetry of the Teflon-encased eye applicator is similar to that of a standard eye applicator. Also, this newly modeled applicator is effective and it can be manufactured for clinical treatment purposes.

Ce mémoire présente les dernières avancées de l'horloge à réseau optique à atomes de Strontium du LNE-SYRTE. Après avoir passé en revue les différents types d'horloges optiques actuellement développées, l'accent est mis sur le concept d'horloge à réseau optique qui a d'abord été formulé dans le cadre d'une horloge à 87Sr utilisant la transition 1S0 - 3P0. Les particularités de cet atome sont présentées, notamment la notion de longueur d'onde magique de piégeage, ainsi que les performances qui sont envisageables pour une telle horloge. La deuxième partie présente les aspects expérimentaux, en insistant plus particulièrement sur le développement du laser ultra-stable qui est utilisé pour l'interrogation des atomes et qui représente un point central. Parmi les dernières améliorations, une phase de pompage optique et d'interrogation en présence d'un champ magnétique a été ajoutée au dispositif de manière à mieux déterminer l'effet Zeeman. Enfin, la dernière partie présente les résultats expérimentaux. La dernière évaluation de l'horloge à 87Sr a permis d'atteindre une exactitude de 2,6.10-15 et une mesure en accord au niveau de 10-15 avec une évaluation indépendante faite au JILA. D'autre part, suite à de récentes propositions théoriques, une mesure a également été effectuée en utilisant l'isotope bosonique 88Sr et en adaptant le dispositif expérimental, permettant d'obtenir la première évaluation pour ce type d'horloge, avec une exactitude de 7.10-14.

The dissolution mechanism and kinetics of a number of strontium master alloys in liquid aluminum and A356 alloys have been investigated. The dissolution behaviour of the strontium alloys was found to show marked differences depending on strontium content. Dilute strontium alloys containing less than 63 weight percent Sr were observed to exhibit simple dissolution in both melts. The dissolution rate and the recoveries of these alloys were found to increase with increasing melt temperature. Over the temperature interval of 675-775$ sp circ$C dissolution was determined to be mass-transfer controlled with associated activation energies of 10-20 kcal/mole. Experimental rate constants for dissolution showed good agreement with a mass transfer correlation expressed as k = (0.67(Gr.Sc)$ sp{1/4}$ + 0.58(h/r)) (D/h). The dissolution of high strontium master alloys $(>$63 wt. pct. Sr), unlike the dilute alloys, was accompanied by the formation of various intermetallics. Additions at low melt temperatures yielded the exothermic formation of those intermetallics that have the lowest Sr content as seen in the relevant phase diagram, i.e., SrAl$ sb4$ in liquid Al and SrAl$ sb2$Si$ sb2$ in liquid A356. Due to low reaction rates at these low melt temperatures, these intermetallics formed as dispersed particles that could easily dissolve in the melt yielding high recoveries. At high melt temperatures, the associated chemical reactions yielded, as products, the higher Sr intermetallics which formed with little or no exothermicity. These intermetallics were observed to be scarcely soluble in the melt resulting in low strontium recoveries. The dissolution times of these alloys were found to show good agreement with calculated values based on a two-stage dissolution model comprising an initial exothermic reaction period and a subsequent free dissolution period. The strontium master alloys were classified in two groups; the high Sr alloys that are efficient at low temperatures of 675-7

Strontium-90 is present in contaminated land at nuclear sites around the world and is also an important component of nuclear waste inventories. The mobility of 90Sr in the subsurface is often controlled either by adsorption to sediment particle surfaces or incorporation reactions into secondary mineral precipitates. This thesis presents the results of a multidisciplinary study examining the behaviour of 90Sr in West Cumbrian unconsolidated aquifer sediments under a range of groundwater and anthropogenic liquor compositions relevant to contaminated land scenarios. Experiments using low ionic strength (IS) regional .groundwater at circumneutral pH found 90Sr was almost completely removed from solution. In higher IS artificial waste tank leachate (PH 11), sorption of 90Sr decreased, suggesting that higher concentration of ions in solution inhibited 90Sr sorption. In both scenarios, EXAFS data confirmed that Sr was present as an outer-sphere adsorption complex. Sorbed 90Sr remained exchangeable with MgCl2 even after one year. In contrast, experiments using pH 13.5 young cement water (YCW), found very high sorption despite the extremely high IS. EXAFS analysis of samples suggested that mineral alteration and the formation of secondary phases had occurred. Secondary phases initially sorbed Sr via inner-sphere adsorption, but in a sample aged for a year at 70 [degree]C there was evidence of Sr incorporation in a newly formed zeolite mineral which was identified as K-chabazite. Once incorporated, Sr was only desorbed using a pH 1.5 solution. Finally, experiments using Ca(OH)2 (PH 12.7) found no evidence of mineral alteration, and sorption was inhibited by the higher ionic strength present.

Since the discovery of superconductivity in Sr2RuO4, there has been intense research interest and efforts on its unconventional pairing symmetry. Although its normal state can be qualitatively described as a quasi-two-dimensional Fermi liquid, surprisingly, Sr2RuO4 turns out to be the prime candidate of the chiral p + ip superconductor, analogous to 3He-A. Such a state is of great interest surrounding, since under a certain conditions it hosts such exotic objects as half-quantum vortices and Majorana bound states, one possible route to an enigmatic quantum computer. Nevertheless, although it is well established now that this superconducting state has odd-parity, and most likely breaks time-reversal symmetry, the negative result on the search of edge current is one of the critical challenges to its chiral p-wave order. These serious discrepancies have even triggered a debate on the primary source of its superconductivity. Motivated by this debate, in this thesis we propose two independent methods to resolve this controversy via “smoking-gun" experiments. First, the vortex structure within the single-band and two-band models is studied within a mean-field theory. The pattern of the local density-of-state at zero bias shows significant anisotropy in the two-band model, while it is nearly isotropic in the single-band case. Also, the spin lattice relaxation rate at the vortex site is greatly enhanced in the single-band case but not in the two-band scenario. These important distinctions stem from the topology of different Fermi surfaces, and can be tested by using standard probes such as scanning tunneling microscope and nuclear magnetic resonance. In the second proposal, we focus on the two-band scenario, and apply a renormalization group theory to explain the form of spin density wave fluctuations. This theory not only reconciles the absence of long range spin density wave order with strongly enhanced fluctuations, but also unveils the mutual exclusion of these fluctuations and p-wave superconducting pairing. Such an exclusion is reflected in the suppression of the spin-spin correlation function at low energies, which can be measured in the inelastic neutron scattering experiment. This suppression, if not observed experimentally, would be a critical challenge to the two-band model, and an indirect but strong support to the assignment of the single γ-band as the primary source of the unconventional pairing.
published_or_final_version
Physics
Doctoral
Doctor of Philosophy

The collection and analysis of a large number of belemnites and oysters with excellent biostratigraphic and diagenetic control has resulted in a highly detailed determination of the seawater Sr-isotope curve through the Jurassic and Early Cretaceous. The new data confirm the broad trends established by previous work, but the much sharper resolution of the new data allows the application of Sr-isotope stratigraphy with an optimal stratigraphic resolution of ± 1 to 4 ammonite subzones (± 0.5 to 2 Ma). The data show a general decline from the Hettangian (Early Jurassic) to a minimum in the Callovian and Oxfordian (Middle/Late Jurassic). This is followed by an increase through the Kimmeridgian (Late Jurassic) to a plateau reached in the Barremian (Early Cretaceous). In addition, there are major negative excursions in the Pliensbachian/Toarcian (Early Jurassic) and Aptian/Albian (Early Cretaceous). Stable isotope data collected from belemnites and oysters have resulted in the most extensive Jurassic δ¹³C and δ¹⁸O database to date. While both the carbon and oxygen data appear to give reasonable marine signals, the scatter in the data suggests that future research must document possible biological fractionation effects and develop better indicators for the diagenetic alteration of 613C and 6i 8O. The final chapter documents an unexpected correlation between sudden shifts in the Sr-isotope curve, the occurrence of positive 513C excursions, and the eruption of flood basalts. In the Jurassic and Cretaceous there is a correlation in time between sudden downward shifts in the Sr-isotope curve (Pliensbachian, Aptian, Cenomanian/Turonian), the occurance of positive 613C excursions, and the eruption of flood basalts. Each of these major downward shifts in the Sr-isotope curve is followed by a sudden upward shift, which although associated with a positive 613C excursion is not associated with an episode of flood basalt volcanism. In the Cenozoic the Sr-isotope curve no longer displays downward shifts, but the correlation continues between the occurrence of flood basalts and positive 513C excursions. Several lines of evidence suggest that the eruption of flood basalts is associated with pulses of hydrothermal activity, and that this hydrothermal activity brings about the conditions necessary for the genesis of carbon-burial events.

Porous strontium-doped apatite-wollastonite scaffolds were evaluated as potential substitutes for enhanced bone regeneration and the prevention of peri-prosthetic infections. Parent glasses of composition 35.5SiO2-7.1MgO-0.4CaF2-7.1P2O5-(49.9-x)CaO-xSrO mol%, where x = 0, 6.2, 12.5, 18.7, 24.9 or 37.4, were produced via the melt-quench route, ground and sieved < 45 μm. Porous scaffolds were obtained following the foam-replication method and heat-treated at 1050 °C for 2 h for controlled nucleation and growth of the crystal phases. All six glasses produced were amorphous. Differential scanning calorimetry showed that the formation of the calcium silicate phase strongly depended on the amount of strontium contained in the parent glass, linearly moving to higher temperatures with increasing strontium. Morphological evaluation (scanning electron microscopy and micro-computed tomography) proved that the obtained scaffold porosity, about 55 vol%, did not depend on the strontium content. X-ray diffraction showed that strontium preferentially substituted in apatite, while only higher strontium compositions formed a strontium magnesium calcium silicate phase. Compressive and biaxial flexural strength were both comparable to cancellous bone. Compositions containing 0 %, 6.2 % and 12.5 % strontium showed excellent apatite forming ability when submerged in simulated body fluid, which then decreased with increasing strontium for the three higher-strontium compositions. Microbiological tests carried out on strontium-containing salts showed no effective antibacterial properties for strontium as a free element. Amongst the six strontium-containing glasses, only the 37.4 % strontium oxide glass showed antimicrobial effects against Pseudomonas aeruginosa in broth dilution tests. Proliferation and osteogenic differentiation of porous scaffolds were tested on human bone cells. No conclusive results were obtained for the G292 cell line. When scaffolds were tested with human primary mesenchymal stromal cells, an increase in DNA content was observed with increasing strontium, while enhanced alkaline phosphatase activity and increased collagen production were found for low strontium compositions.

The Tonian Period (1000 - c.720 Ma) followed a long interval of relative stasis, in terms of climate, carbon isotopes and biological evolution, and led into the Cryogenian Period of environmental extremes and instability. Despite its pivotal situation, the Tonian Period is still relatively understudied, and this is partly due to the lack of robust age constraints in key Proterozoic successions around the world. The fossiliferous Neoproterozoic strata of the North China craton were until recently thought to be of Ediacaran age. However, fossil evidence and new geochronological constraints combine to show that most of the ‘Qingbaikou’ System, which reaches a great thickness in some areas, was deposited between c. 980 and c. 920 Ma. The isotopic signature of these strata confirms their Tonian age, showing typical moderately high 13C values together with low 87Sr/87Sr ratios, < 0.7065. Another characteristically Tonian feature is the unusually widespread abundance of early diagenetic ‘molar-tooth’ low-Mg calcite microspar. In this study, I compare MT samples with their surrounding ‘bulk’ matrix in correlative successions on the North China craton in order to 1) demonstrate their propensity to preserve a primary seawater isotopic signature; and 2) reconstruct, together with published data, the strontium (and carbon) isotopic evolution of early Tonian seawater. Second-order fluctuations of less than ~0.001 are superimposed on a general 87Sr/87Sr rise from ~0.7052 to ~0.7063 by c. 920 Ma, accompanied by a profoundly negative carbon isotope excursion. Increased chemical weathering has been linked with both climatic and carbon isotope instability, and this study indicates an earlier beginning to such carbon cycle perturbations, which coincide with early stages of supercontinent rifting, as evidenced by the newly dated Dashigou igneous province of North China. These and other new and published data are used to reconstruct and reinterpret the strontium isotopic evolution of Neoproterozoic seawater.

This work presents the realisation and characterisation of the world’s smallest transportable optical lattice clock as part of the Space Optical Clocks 2 EU project built at the University of Birmingham. Housed in a transportable rack of dimensions 170 x 100 x 60 cm, such a device aims to measure the frequency of the doubly-forbidden 1S0−3P0 clock transition in 88Sr in an unprecedented compact apparatus as a major technological milestone towards an optical clock upon the International Space Station. A master optical clock in space would serve with unrivalled accuracy and stability to disseminate a precise and accurate reference for terrestrial clocks and the coordination of international time. Such a clock has the potential to redefine the second, revolutionise timekeeping and precision measurements, and perform fundamental science experiments in space. Using a combination of novel design, innovative cooling techniques, and robust, compact commercially available products, the clock portability, robustness and operational simplicity have been improved. The apparatus simply and effectively cools and traps up to 105 88Sr atoms at a temperature of 1.3±0.2μK in an optical lattice with a lifetime of 0.52±0.01s within 400ms. The most recent preliminary clock spectroscopy measurement was 3.6 ± 0.2Hz. The instability of the clock has been measured at 8×10−17 after averaging for 300s with the goal instability being 5.8×10−17 within the same averaging time. These results show the experiment will lead transportable optical clock research and continue with the goal of being a master clock in space.

Doutoramento em Ciência e Engenharia de Materiais
O SrTiO3 (ST) cristaliza com a estrutura da perovesquite e apresenta propriedades de um paraeléctrico quântico; isto é, exibe um aumento continuo da permitividade dieléctrica com o decréscimo da temperatura até 4K, seguido de um patamar de valor constante até cerca de 0K. A presença de imperfeições na rede, tais como defeitos pontuais, impurezas e tensões podem modificar apreciavelmente as propriedades do ST puro e mesmo induzir ferroelectricidade. Neste trabalho foi conduzido um estudo sistemático da estrutura, microestrutura e comportamento dieléctrico de filmes finos não dopados e dopados de ST policristalino preparados por sol gel e depositados sobre diferentes substratos. As propriedades dieléctricas foram estudadas numa gama alargada de temperatura e frequência do campo eléctrico. A caracterização dieléctrica dos filmes foi efectuada em função da temperatura e frequência desde o regime das frequências rádio (rf), terahertz (THz-TDS) e infra vermelho (IR). As características cristalográficas e microestuturais dos filmes de ST foram analisadas por difracção de raios X (DRX), espectroscopia de Raman, microscopia electrónica de varrimento (SEM) e de transmissão (TEM), espectroscopia de Rutherford Backscattering (RBS). Foi feito um estudo detalhado da dinâmica de rede destes materiais. É mostrado neste trabalho que filmes finos de ST não dopados e crescidos em diferentes substratos (Al2O3/Pt, Si/SiO2/TiO2/Pt, (LaAlO3)0.3- (Sr2AlTaO6)0.7/Pt, SrTiO3/Pt and MgO/Pt) apresentam diferentes características estruturais e propriedades eléctricas, directamente dependentes das tensões criadas nos filmes. Nos grãos dos filmes de ST depositados sobre substratos de MgO/Pt devido às elevadas tensões compressivas originadas pelo substrato observam-se deslocações do tipo “slip band dislocations”, Enquanto que o modo TO1 de filmes de ST depositados sobre Al2O3 se comporta de maneira muito semelhante aos cristais de ST na gama de temperatura entre 300K e 150K, o modo TO1 dos filmes de ST depositados sobre substratos de MgO apresenta-se endurecido, o que se pode explicar pela influência das tensões geradas nos filmes pelo substrato. Filmes de ST com as tensões compressivas mais elevadas, depositados sobre substratos de MgO/Pt exibem os valores mais elevados da parte real da permitividade dieléctrica (ε′), a maior resposta histerética da polarização em função do campo eléctrico aplicado e os maiores valores da sintonabilidade dieléctrica (nr), em oposição aos filmes de ST, depositados sobre substratos de Al2O3/Pt com as tensões tractoras mais elevadas. Neste trabalho é também salientada a importância dos aspectos tecnológicos da preparação por sol gel, na qualidade dos filmes finos de ST, que se reflecte nos valores elevados de ε′ and nr, que são obtidos por pela introdução de camadas intermédias tampão (buffer layers) e pelo aumento da temperatura de queima de 750o C para 900o C. Com base em previsões teóricas, de que o deslocamento de iões de pequenas dimensões (“off centre”) como o Mg, nos locais dos iões Sr da rede induzem uma anomalia na resposta dieléctrica do ST, foi estudada a incorporação de Mg na rede dos filmes de ST. Foi observado que o limite de solubilidade sólida de Mg na rede de ST é dependente do local da rede no qual ocorre a incorporação do dopante e da temperatura do tratamento térmico. Aumentando a temperatura do tratamento térmico decresce a solubilidade do magnésio nos filmes de Sr1-xMgxTiO3 de x > 0.30 a 750o C para x < 0.15 a 900o C. De acordo com este estudo, o Mg não induz um estado ferroeléctrico nem um comportamento do tipo relaxor em filmes finos de titanato de estrôncio preparados por sol gel, quer quando a substituição ocorre nos locais A ou B da rede do ST. A estrutura, dinâmica de rede e propriedades dieléctricas de filmes finos de ST dopados com Bi são também apresentados neste trabalho e discutidos pela primeira vez. Nos filmes de Sr1-1.5xBixTiO3 o modo TO1 torna-se mais duro e independente da temperatura e uma relaxação a baixas frequências aparece com o aumento do conteúdo de Bi. A posição do máximo de ε′ dos filmes estudados desloca-se para temperaturas mais altas com o aumento da concentração de Bi e com o aumento da frequência. A presença de “clusters” de dimensões nanométricas e dos iões de Bi em posição “off centre” causa uma relaxação dieléctrica complexa. A relaxação dieléctrica induzida segue, a lei de Arrhenius para as amostras com baixo teor de Bi (x < 0.04), e a relação de Vogel-Fulcher para as amostras com as concentrações de dopante mais elevadas (0.04 ≤ x ≤ 0.167). A dispersão da frequência de ε′ em filmes finos de Sr1-1.5xBixTiO3 com pequenos teores de Bi é ligeiramente suprimida, quando em comparação com os cerâmicos correspondentes, o que pode ser explicado pela influência do substrato no caso dos filmes finos. Este estudo ilustra que a incorporação de Bi na rede de ST origina um comportamento do tipo relaxor, aumentando a tunabilidade dieléctrica. Filmes finos de Sr1-1.5xBixTiO3 com elevados factores de qualidade (> 2000 numa gama de temperatura alargada) são candidatos apropriados para utilização em sintonizadores.
SrTiO3 (ST), crystallizing in the perovskite type structure, is a quantum paraelectric, i.e., it exhibits a continuous increase of the dielectric permittivity with decreasing temperature down to 4K, followed by the levelling off of the permittivity to near 0K. The presence of lattice imperfections such as strain, point defects, grain boundaries, and impurity atoms can appreciably modify the properties of pure ST and even induce ferroelectricity. In this work, systematic research on the structure, microstructure and dielectric behaviour of polycrystalline SrTiO3 - based thin films prepared by solgel is performed. The dielectric properties are studied in a wide temperature, frequency and electric field ranges. For some films the dielectric characterisation is assessed at radio-frequency (rf), time-domain terahertz (THz-TDS), and infrared (IR) spectroscopy. The crystallographic and micro structures of the undoped and doped ST films are analysed by X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and Rutherford Backscattering Spectrometry (RBS) techniques. Detailed investigations of the lattice dynamics in a wide frequency range is undertaken as well. It was observed, that undoped ST films grown on different substrates (Al2O3/Pt, Si/SiO2/TiO2/Pt, (LaAlO3)0.3-(Sr2AlTaO6)0.7/Pt, SrTiO3/Pt and MgO/Pt) have different structural and dielectric properties dependent on the strain/stress effect induced by the substrate. For the case of ST films on MgO substrates the appearance of some “slip band dislocations” within the film grains was detected due to the high compressive stresses from the substrate. Whereas TO1 mode of ST films deposited on Al2O3 behaves similarly to that of ST single crystals in the temperature range from 300K to 150K. TO1 mode of ST films deposited on MgO substrate is stiffened, what can also be explained by influence of the stresses. ST films, with the highest compressive stress, deposited on MgO/Pt substrate shows the highest value of the real part of the dielectric permittivity (ε′), the largest hysteresis loop, and the highest value of the dielectric tunability (nr) in opposition to ST films, with the highest tensile stress, deposited on Al2O3/Pt substrates. The role of the technological aspects associated with the preparation of highquality sol-gel ST films is reflected in the elevated ε′ and nr of ST films, obtained by introducing buffer layers, intermediately annealed at 600o C, and by increasing films annealing temperature from 750o C to 900o C. As a consequence ε′ and nr of ~700 and ~50% are attained, being among the highest values reported for ST sol gel based films. Based on the theoretical prediction, that the off-centre displacements of small Mg ions at the large Sr sites can induce dielectric anomalies in ST, the incorporation of Mg in ST films was addressed in this work. Solid solubility limit of Mg was found to depend on the lattice site of incorporation and annealing temperature. Increasing annealing temperature decreases the solubility in Sr1-xMgxTiO3 thin films from x > 0.30 for 750o C to x < 0.15 at 900o C. Moreover Mg does not induce ferroelectricity or relaxor-like behaviour in strontium titanate, either located in A- or B-site of the SrTiO3 lattice. Within this work, the structure, low temperature lattice dynamics and dielectric properties of Bi doped ST films are described and discussed for the first time. In Sr1-1.5xBixTiO3 films TO1 mode becomes harder and, concomitantly a temperature independent and low-frequency relaxation appears with increasing of Bi content. The position of the maximum of ε′ of the investigated films shifts to high temperatures with increasing Bi content and frequency. The presence of nanoclusters and off-centred Bi ions causes a complex relaxation dynamics in these films. The induced dielectric relaxation follows the Arrhenius law for the samples with low Bi content (x < 0.04) and the Vogel-Fulcher law for the samples with a higher doping concentration (0.04 ≤ x ≤ 0.167). The frequency dispersion of ε′ in Sr1-1.5xBixTiO3 thin films with small amount of the Bi is slightly suppressed, compared to the corresponding ceramics, what can be explained by the influence of substrate. Bi incorporation in ST lattice leads to a relaxortype dielectric response, increasing the dielectric tunability. Sr1-1.5xBixTiO3 thin films with high value of the quality factor (> 2000 in wide temperature range) are appropriate candidates for using in tunable applications.