Gotowa bibliografia na temat „Sn-Te alloys”

Thermoelectric (TE) materials are of great interest to many researchers because they directly convert electric and thermal energy in a solid state. Various materials such as chalcogenides, clathrates, skutterudites, eutectic alloys, and intermetallic alloys have been explored for TE applications. The Ga-Sn-Te system exhibits promising potential as an alternative to the lead telluride (PbTe) based alloys, which are harmful to environments because of Pb toxicity. Therefore, in this study, thermodynamic optimization and critical evaluation of binary Ga-Sn, binary Sn-Te, and ternary Ga-Sn-Te systems have been carried out over the whole composition range from room temperature to above liquidus temperature using the CALPHAD method. It is observed that Sn-Te and Ga-Te liquids show the strong negative deviation from the ideal solution behavior. In contrast, the Ga-Sn liquid solution has a positive mixing enthalpy. These different thermodynamic properties of liquid solution were explicitly described using Modified Quasichemical Model (MQM) in the pair approximation. The asymmetry of ternary liquid solution in the Ga-Sn-Te system was considered by adopting the toop-like interpolation method based on the intrinsic property of each binary. The solid phase of SnTe was optimized using Compound Energy Formalism (CEF) to explain the high temperature homogeneity range, whereas solid solution, Body-Centered Tetragonal (BCT) was optimized using a regular solution model. Thermodynamic properties and phase diagram in the Ga-Sn-Te and its sub-systems were reproduced successfully by the optimized model parameters. Using the developed database, we also suggested several ternary eutectic compositions for designing TE alloy with improved properties.

Reactions of molten Sn–xCu (x = 0.05 to 1.0) alloys with Te substrate at 250 °C were investigated. A dosage of 0.1 wt% Cu in Sn is found to be effective in suppressing the vigorous Sn/Te reaction by forming a thin CuTe at the solder/Te interface. The CuTe morphology changes from irregular clusters into a layered structure with increasing Cu content in Sn. With the same reaction time, the CuTe thickness increases proportionally to the square root of Cu content in Sn–Cu alloys, suggesting a diffusion-controlled growth for CuTe.

The present article deals with the differential thermal analyses (DTA) study of Se–Te glasses containing Sn. DTA runs are taken at six different heating rates (5, 10, 15, 18, 20, and 22 K min−1). The crystallization data are examined in terms of modified Kissinger, Mahadevan method, and Augis and Bennett approximation for the non-isothermal crystallization. Results of DTA under non-isothermal conditions on the glasses of the Se80Te20--xSnx (x = 3 and 9) are reported and discussed at different heating rates. The glass transition temperatures (Tg), the onset crystallization temperatures (Tc), and the peak temperature of crystallization (Tp) were found to be dependent on the compositions and the heating rates. From the dependence on heating rates of (Tg) and (Tp) the activation energy for glass transition (Eg) and the activation energy for crystallization (Ec) are calculated and their composition dependence discussed.

AbstractThe formation of antisite defects in Ge_20Te_80 and Ge_15As_4Te_81 vitreous alloys in the form of tin atoms in tellurium sites and tellurium atoms in germanium sites is shown by emission Mössbauer spectroscopy with the ^119 mm Sn(^119 m Sn), ^119 m Te(^119 m Sn), ^125Sn(^125Te), and ^125 m Te(^125Te) isotopes. It is shown that the isovalent substitution of germanium atoms by tin atoms does not vary the symmetry of the local surrounding of germanium sites, while tin and tellurium atoms reconstruct their local surrounding in sites unnatural for them.

AbstractFrom neutron and X-ray diffraction investigations on liquid Ge15Te85, Sn16Te84 and Pb14.5Te85.5 alloys the coordination numbers and nearest neighbour distances of these systems are obtained. The partial structure factors and partial pair correlations reveal that the short-range order of the eutectic Ge -Te melt differs from that of the eutectic Sn-Te and Pb-Te melts

Conselho Nacional de Desenvolvimento Científico e Tecnológico
In this work it is proposed the development of flow injection systems for hydride generation coupled to inductively coupled plasma mass spectrometry (FI-HG-ICPMS) for determination of trace elements (As, Bi, Sb, Se, Sn and Te) in lead alloys employed in automotive battery. Due to the characteristics of the sample matrix, manly the presence of high concentrations of lead that can interfere in hydride generation technique, a detailed investigation of the influence of the physical and chemical parameters was made. The carrier solution concentration (HCl) reductant concentration (NaBH4 solution), reaction coil length and sample volume were evaluated. As the ICP-MS is a multielmentar technique, the parameters were optimized in order to determine simultaneously the highest number of elements. Three different configurations of FI systems were tested: a) a single channel system; b) a two channel system with one gas/liquid separator; and, c) a two channel system with two gas/liquid separators. According to the characteristics of the elements, two groups were separated: one group containing As, Bi, Se and Te were 6.0 mol l-1 HCl is necessary as sample carrier solution and another group containing Sb and Sn were 0.1 mol l-1 HCl is used as sample carrier. The compromise conditions of NaBH4 concentration, carrier gas (Ar) flow rate, sample volume and reactor coil length were 0.6% (m/v), 1.25 L min-1, 87 μL and 50 cm, respectively, for both groups of elements. Both systems with two reaction channels allow the simultaneous determination of the two groups of elements. Strong analyte signal suppression in presence of Pb, Ag, Bi and Cu was observed. However, the interference could be overcome by using the optimized conditions for hydride generation. By using the proposed FI-HG-ICP-MS systems it was possible to determine relatively low concentrations of Bi, Sb, Se, Sn and Te in lead alloys. The limits of detection were 0.34, 0.01, 0.01, 0.01, 0.01, 0.01 mg g-1 of As, Bi, Sb, Se, Sn and Te, respectively. The accuracy of the developed method was evaluated by using analyte recovery tests where the results were in range 94 to 103%.
Neste trabalho foram desenvolvidos sistemas de injeção em fluxo (FI) para a geração de hidretos (HG) acoplados a espectrometria de massa com plasma indutivamente acoplado (FI-HG-ICP-MS), para a determinação de elementos traço em liga de chumbo empregada em baterias automotivas. Devido às características da matriz da amostra, principalmente devido a presença de Pb, foi feita uma investigação detalhada dos parâmetros físicos e químicos da HG como, a concentração da solução carregadora (HCl), concentração do redutor, comprimento do reator e o volume de amostra injetado. Para a eficiente geração dos hidretos voláteis foi necessário estabelecer uma condição de compromisso. Desta forma, para As, Bi, Se e Te foi usada como solução carregadora da amostra HCl 6,0 mol L-1 e HCl 0,1 mol L-1 para Sb e Sn. A concentração de NaBH4, vazão do gás de arraste (Ar), volume de amostra injetado e o comprimento do reator foram 0,6% (m/v), 1,25 L min-1, 87 μL e 50 cm, respectivamente, para ambos os grupos de elementos. Após estabelecidas as condições reacionais para a geração de hidretos, foram desenvolvidos três sistemas FI. Um sistema FI com um canal de reação e dois sistemas com dois canais de reação, com um e dois separadores gás-líquido. Os sistemas com dois canais de reação permitem a determinação simultânea dos dois grupos de elementos. Forte supressão de sinal foi observada na presença de Pb, Ag, Bi e Cu porém, estas foram contornadas, particularmente, pelas condições reacionais da geração de hidretos e o reduzido volume de amostra injetado. Desta forma, utilizando os sistemas propostos foi possível a determinação de concentrações relativamente baixas para Bi, Sb, Se, Sn e Te em amostras de liga de chumbo. Os limites de detecção obtidos foram de 0,34, 0,01, 0,01, 0,01, 0,01, 0,01 mg g-1 para As, Bi, Sb, Se, Sn e Te, respectivamente. A exatidão do método proposto foi avaliada através de teste de recuperação dos analitos, sendo que os mesmos ficaram na faixa entre 94 e 103%.

The basic concept of thermoelectricity is the conversion of dissipated heat into electricity with applications in the areas such as automobile engineering, refrigerating coolants, satellites, etc. The thermoelectric figure of merit,zT=((S^2 σ)/κ) T, is the defining factor for thermoelectric materials, which attributes to the power factor (P=S2σ, σ-electrical conductivity S-Seebeck coefficient) enhancement and thermal conductivity reduction. Power factor can be improved by bandgap tuning and carrier concentration, whereas thermal conductivity can be reduced through grain size reduction, point defects, and dislocations. These can be achieved experimentally through microstructural engineering and processing. Microstructure can be tuned by varying volume fraction, morphology variation, inclusion of nano, 2D structures etc. Fine-tuning of microstructure is one of the key factors in improving thermoelectric properties. Creating interfaces through incorporation of multiple phases, self-organised eutectic composites are efficient ways to reduce thermal conductivity. In this thesis, we have chosen to investigate the thermoelectric properties of Sn-Te based alloys with microstructural studies which can be divided into three parts as follows. The synthesis and properties of thermoelectric off eutectic and eutectic composites of the Sn-Te binary system are presented in the preliminary part of the investigation. Hypo eutectic alloys are SnTe rich, and hyper eutectic alloys are towards the phase diagram’s Te rich side with Te and SnTe phase mixture. Interfaces between SnTe and Te phases and the presence of primary and eutectic phase mixture do affect the mobility of charge carriers giving rise to optimized electrical transport properties. The second part consists of the influence of morphological variation of a eutectic composite of SnTe and Te on thermoelectric properties. Microstructural variations obtained by solidifying eutectic composite via furnace, air, oil, water, and (water + glycol) were characterized to understand the microstructural evolution. Novel result of transformation from rod-lamellar was revealed in the eutectic microstructures. Thermoelectric potential of these alloys were explored. Various factors contributing to increased power factor and decreased thermal conductivity was analysed. The effect of cooling rate on overall Figure of merit (FOM) was studied. The third part consists of the third element addition to the Sn-Te binary system. Upon the addition of Sb to the Sn-Te system, ternary eutectics have displayed improved electron transport properties. Contribution of each phase present in the alloy towards the improvement of electron transport properties was explored. Further due to microstructural complexity, thermal conductivity is expected to be reduced. This work consists of robust microstructural modification along with improving thermoelectric properties.

Solidification of eutectic systems delivers compelling examples of microstructure formation, which makes the phenomena intriguing to many engineers and scientists. Therefore, eutectic solidification is extensively studied experimentally, theoretically, and numerically. However, some exotic eutectic microstructures are still not understood, particularly the systems that exhibit anisotropy. The main objective of this thesis is to explore the microstructure formation in exotic systems during solidification. As directional solidification is a convenient way (imposes the temperature gradient, solidification velocity accurately and independently) to study the microstructure formation, the first part of the work was directed towards the development of directional solidification configuration. Subsequently, we investigated the microstructure formation in three different exotic eutectic systems. In the first system (Sn-Zn eutectic), we study the formation of two-phase microstructures with endeavors to bring new inferences, as the volume percentage of the (Zn)-phase in the eutectic is less than 10%, so one would expect it to form rods in the matrix of (Sn)-phase; instead, thin lamellae are observed. We claim that the rod-lamellar transition and well-defined lamellar orientation are due to the anisotropy of the free energy of the solid-solid interfaces. We deploy various methods/experiments for confirming the evidence of solid-solid interface anisotropy. We also provide the crystallographic orientation relationships between BCT-(Sn) and HCP-(Zn) in steady-state microstructures. In the second system (SnTe-Te eutectic), we investigate the evolution of complex patterns due to the addition of ternary impurities in the Sn-Te eutectic system that contains trigonal (Te) and an intermetallic SnTe phase with a cubic crystal structure. In this work, we examine the origin of such a microstructure that arises due to a two-phase growth instability induced by impurity addition. The binary eutectics (Sn-Te) and ternary eutectics (Sn-Te with an impurity addition) are directionally solidified at different interfacial velocities in order to study morphological evolution. The binary alloy exhibits a rod-like or an interconnected string of rods morphology, while the addition of a third component leads to a diffusive instability (similar to a Mullins-Sekerka instability) that results in the formation of two-phase colonies. The onset of instability depends on both the growth velocity and impurity concentration, while the growth direction of the cells is normal to the (0001) of (Te) and (111) of SnTe. Through the extensive use of multiple characterization techniques, we have explored the morphological characteristics and crystallography of these colonies. The colonies have a complex internal structure that bears a three-fold symmetry reminiscent of the trigonal symmetry of the (Te) crystal, arising possibly because of strong anisotropy in the solid-liquid interfacial energy or in the kinetics of growth. For the different impurity additions (Ag, Cu, Ge, In, Sb), the internal eutectic morphology of the colony due to the addition of Ag, Cu, Ge, In is different from that observed for the addition of Sb. The latter leads to the formation of lamellae, while a rod-like feature could be observed for impurities Ag, Cu, Ge, In. In the third system (Ag-Cu-Sb), we have investigated the formation of three-phase microstructures of the Ag-Cu-Sb eutectic system that contains two intermetallic compounds, i.e., silver antimonide-Ag3Sb, copper antimonide-Cu2Sb and an antimony rich solid-solution (Sb). A vast range of microstructures in this system arise due to the possibilities of both invariant reactions giving rise to three-phase eutectic growth as well univariant reactions that are amenable to diffusive instabilities giving rise to microstructures involving two-phase colonies along with three-phase eutectic morphologies. The different ternary compositions are morphologically and crystallographically investigated at various velocities. The invariant three-phase eutectic reactions give rise to exotic hollow, dog bone, and fibrous (Sb) crystals along with lamellar/rod type morphologies of the Cu2Sb phase, while the Ag3Sb has a continuous morphology. The different microstructures have an underlying crystallographic basis and distinct growth mechanisms that are influenced by the crystal orientation with the imposed temperature gradient. Among the compositions that give rise to two-phase colonies, an exciting structure emerges in the Ag3Sb-(Sb) two-phase colonies that exhibit a complex 3-fold fish skeleton structure reminiscent of the rhombohedral (Sb) crystals. Similarly, the Ag3Sb-Cu2Sb colonies exhibit a complex plate morphology influenced by the anisotropic nature of the Ag3Sb-Cu2Sb interface.