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1
Carter, C. Barry, i Lisa A. Tietz. "Interfaces in high-Tc superconducting oxides". Proceedings, annual meeting, Electron Microscopy Society of America 47 (6.08.1989): 178–79. http://dx.doi.org/10.1017/s0424820100152860.
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Interfaces in high-Tc superconducting oxides are influential during both the processing of bulk materials and the growth of thin epitactically aligned layers. In the first case, the formation of the superconducting phase involves the movement of phase boundaries during the solid-state reaction, while in the second, the phase boundary is formed as the superconducting material grows on the single-crystal substrate. Having formed the superconducting material, the superconducting phase will, in general, contain a large number of grain boundaries varying from the simple twin boundaries which can be produced during the cubic-to-tetragonal transformation, to low-angle grain boundaries, special high-angle grain boundaries, other high-angle grain boundaries and phase boundaries due to incomplete or on-going solid-state reactions. During the course of this presentation, recent results on these topics will be reviewed, paying particular attention to the more widely studied material, YBa2Cu3O6+x.The importance of grain boundaries in high-Tc superconducting oxides has been firmly established by the systematic analysis of Dimos et al who have shown that the misorientation of the grains in layers of YBa2Cu3O6+x which had been grown on polycrystalline SrTiO3 substrate varies with the relative misorientation between the grains.
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Yoshida, Hidehiro, Koji Morita, Byung Nam Kim, Keijiro Hiraga, Takahisa Yamamoto, Yuichi Ikuhara i Taketo Sakuma. "High Temperature Plastic Flow and Ductility in Polycrystalline Oxide Ceramics: Doping Effect and Related Phenomena". Advances in Science and Technology 45 (październik 2006): 1620–25. http://dx.doi.org/10.4028/www.scientific.net/ast.45.1620.
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High temperature creep and superplastic flow in high-purity oxide ceramics such as alumina and tetragonal zirconia polycrystals is very sensitive to a small amount of doping by various oxides. High-resolution transmission electron microscopy and an energy-dispersive X-ray spectroscopy analysis revealed that grain boundaries in high-purity oxide ceramics are free from amorphous phase, and that the doped cations tend to segregate along the grain boundaries. Since the high temperature plastic flow in oxide ceramics takes place mainly by grain boundary matter transport by atomic diffusion, the grain boundary nano-structure control must be a useful way to develop new high-performance functional ceramics in the near future.
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Nguyen, Viet Huong, Ulrich Gottlieb, Anthony Valla, Delfina Muñoz, Daniel Bellet i David Muñoz-Rojas. "Electron tunneling through grain boundaries in transparent conductive oxides and implications for electrical conductivity: the case of ZnO:Al thin films". Materials Horizons 5, nr 4 (2018): 715–26. http://dx.doi.org/10.1039/c8mh00402a.
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OSHIO, T., Y. SAKAI i S. EHARA. "STM STUDY OF POLYCRYSTALLINE COPPER". Modern Physics Letters B 04, nr 22 (grudzień 1990): 1411–14. http://dx.doi.org/10.1142/s021798499000177x.
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Grain boundaries and their electric potential were studied in connection with the electric conduction in polycrystalline copper using a scanning tunneling microscope (STM). It was found that the grain boundaries consist mainly of cuprous oxide ( Cu 2 O ) and electric potential barriers are formed at most grain boundaries.
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Moriyama, Takumi, Sohta Hida, Takahiro Yamasaki, Takahisa Ohno, Satoru Kishida i Kentaro Kinoshita. "Experimental and Theoretical Studies of Resistive Switching in Grain Boundaries of Polycrystalline Transition Metal Oxide Film". MRS Advances 2, nr 4 (2017): 229–34. http://dx.doi.org/10.1557/adv.2017.7.
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ABSTRACTPractical use of Resistive Random Access Memory (ReRAM) depends on thorough understanding of the resistive switching (RS) mechanism in polycrystalline metal oxide films. Based on experimental and theoretical results of NiO based ReRAM, we have proposed a grain surface tiling model, in which grain surfaces (i.e. grain boundaries) are composed by insulating and conductive micro surface structures. This paper reports the adequacy of our model to the NiO based ReRAM and universality of surface electronic properties in metal oxides of NiO, CoO and MgO. Experimental results of RS operating modes suggest that the resistance changes in the grain boundaries, supporting our model. First-principles calculation results suggest that our model can be adopted to other metal oxide materials and the RS from a low resistance to a high resistance can be caused at 1000 K, which agrees with previous experimental reports.
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Welsh, Shery L., Monica Kapoor, Olivia D. Underwood, Richard L. Martens, Gregory B. Thompson i Jeffrey L. Evans. "Influence of Grain Boundary Character and Annealing Time on Segregation in Commercially Pure Nickel". Journal of Materials 2016 (16.02.2016): 1–15. http://dx.doi.org/10.1155/2016/4597271.
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Commercially pure nickel (Ni) was thermomechanically processed to promote an increase in Σ3 special grain boundaries. Engineering the character and chemistry of Σ3 grain boundaries in polycrystalline materials can help in improving physical, chemical, and mechanical properties leading to improved performance. Type-specific grain boundaries (special and random) were characterized using electron backscatter diffraction and the segregation behavior of elements such as Si, Al, C, O, P, Cr, Mg, Mn, B, and Fe, at the atomic level, was studied as a function of grain boundary character using atom probe tomography. These results showed that the random grain boundaries were enriched with impurities to include metal oxides, while Σ3 special grain boundaries showed little to no impurities at the grain boundaries. In addition, the influence of annealing time on the concentration of segregants on random grain boundaries was analyzed and showed clear evidence of increased concentration of segregants as annealing time was increased.
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Vahidi, Hasti, Komal Syed, Huiming Guo, Xin Wang, Jenna Laurice Wardini, Jenny Martinez i William John Bowman. "A Review of Grain Boundary and Heterointerface Characterization in Polycrystalline Oxides by (Scanning) Transmission Electron Microscopy". Crystals 11, nr 8 (28.07.2021): 878. http://dx.doi.org/10.3390/cryst11080878.
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Interfaces such as grain boundaries (GBs) and heterointerfaces (HIs) are known to play a crucial role in structure-property relationships of polycrystalline materials. While several methods have been used to characterize such interfaces, advanced transmission electron microscopy (TEM) and scanning TEM (STEM) techniques have proven to be uniquely powerful tools, enabling quantification of atomic structure, electronic structure, chemistry, order/disorder, and point defect distributions below the atomic scale. This review focuses on recent progress in characterization of polycrystalline oxide interfaces using S/TEM techniques including imaging, analytical spectroscopies such as energy dispersive X-ray spectroscopy (EDXS) and electron energy-loss spectroscopy (EELS) and scanning diffraction methods such as precession electron nano diffraction (PEND) and 4D-STEM. First, a brief introduction to interfaces, GBs, HIs, and relevant techniques is given. Then, experimental studies which directly correlate GB/HI S/TEM characterization with measured properties of polycrystalline oxides are presented to both strengthen our understanding of these interfaces, and to demonstrate the instrumental capabilities available in the S/TEM. Finally, existing challenges and future development opportunities are discussed. In summary, this article is prepared as a guide for scientists and engineers interested in learning about, and/or using advanced S/TEM techniques to characterize interfaces in polycrystalline materials, particularly ceramic oxides.
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Cho, Yong S., David T. Hoelzer, Vernon L. Burdick i Vasantha R. W. Amarakoon. "Grain boundaries and growth kinetics of polycrystalline ferrimagnetic oxides with chemical additives". Journal of Applied Physics 85, nr 8 (15.04.1999): 5220–22. http://dx.doi.org/10.1063/1.369949.
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Zaborac, J. A., J. P. Buban, H. O. Moltaji, S. Stemmer i N. D. Browning. "Cation Coordination At Σ Grain Boundaries in TiO2 and SrTiO3, and its Effect on the Local Electronic Properties". Microscopy and Microanalysis 5, S2 (sierpień 1999): 792–93. http://dx.doi.org/10.1017/s1431927600017281.
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Grain boundaries have long been known to have a dominant effect on the electronic properties of polycrystalline materials. In the case of electroceramic oxides, the thermodynamics of defect formation (vacancies or interstitials, cations or anions) are usually invoked to predict the presence of a space charge potential at the grain boundaries. The relative energetics for the formation of each type of defect determines the size and sign of this potential barrier and thus, the effect that boundaries have on the overall electronic properties of the materials. However, a limitation to this continuum thermodynamics approach is that it does not consider the effect of the grain boundary structure.To investigate whether the grain boundary atomic structure can have an effect on the energetics of defect formation and hence the electronic properties, here we examine the structure of Σ5 boundaries in two systems, SrTiO3 (perovskite) and TiO2(rutile).
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Prabhumirashi, Pradyumna L., Kevin D. Johnson i Vinayak P. Dravid. "Predictive Structure-Property Correlations for SrtiO3 Grain Boundaries". Microscopy and Microanalysis 7, S2 (sierpień 2001): 292–93. http://dx.doi.org/10.1017/s1431927600027537.
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In polycrystalline materials the trapping of charge at interfaces has a decisive influence on the electrical transport properties through the formation of electrostatic potential barriers. This can either be an intrinsic phenomenon or can be related to impurity segregation leading to complex defect centers. This plays a key role in technologically important systems, especially those having electrically active interfaces, e.g.,p-n junctions in semiconductors and grain boundaries in electroceramics.Electroceramic oxides such as ZnO and SrTiO3 are common systems that exhibit the tendency of current control by internal potential barriers. While bulk measurements, either electrical (e.g. P-E, C-V, I-V), or optical (e.g. Raman) have contributed significantly to the understanding of charged interfaces, there are a very few direct observations of electrical activity at a nanometer level. For instance, it has been recognized that space charge and dopant segregation at the grain boundary are inter-related.
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Rathore, Divya, Chenxi Geng, Nafiseh Zaker, Ines Hamam, Yulong Liu, Penghao Xiao, Gianluigi A. Botton, Jeff Dahn i Chongyin Yang. "Tungsten Infused Grain Boundaries Enabling Universal Performance Enhancement of Co-Free Ni-Rich Cathode Materials". Journal of The Electrochemical Society 168, nr 12 (1.12.2021): 120514. http://dx.doi.org/10.1149/1945-7111/ac3c26.
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Ni-rich cathode materials suffer from poor capacity retention due to micro-cracking and interfacial reactivity with electrolyte. Addition of tungsten (W) to some Ni-rich materials can improve capacity retention. Here, a WO3 surface coating is applied on Ni-rich hydroxide precursors before heating with lithium hydroxide. After heating in oxygen, Ni-rich materials with any of the commonly used dopants (magnesium, aluminum, manganese, etc.) show a “universal” improvement in capacity retention. Experimental characterization and theoretical modelling showed W was concentrated in the grain boundaries between the primary grains of secondary particles of the layered oxides, and W is incorporated in amorphous LixWyOz phases rather than as a substituent in the LiNiO2 lattice. This self-infusion of W in the grain boundaries during synthesis also significantly restricts primary crystallite grain growth. Along with smaller primary grain size, the LixWyOz phases in the grain boundaries lead to improved resistance to microcracking and reduced surface or interfacial reactivity. Improving the intrinsic properties of primary grains through doping of Mg, Al, or Mn and reinforcing the secondary particle structure mechanically and chemically using W or a similar element, M, that forms LixMOy phases and does not substitute into LiNiO2 is a universal strategy to improve polycrystalline Ni-rich materials.
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Wang, Xiao, i Alfred Ludwig. "Recent Developments in Small-Scale Shape Memory Oxides". Shape Memory and Superelasticity 6, nr 3 (26.08.2020): 287–300. http://dx.doi.org/10.1007/s40830-020-00299-7.
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Abstract This review presents an overview of the developments in small-scale shape memory materials: from alloys to oxides and ceramics. Shape memory oxides such as zirconia, different ferroelectric perovskites and VO2-based materials have favorable characteristics of high strength, high operating temperature and chemical resistance, which make this class of shape memory materials interesting for special applications, e.g., in harsh environments or at the nanoscale. Because of the constraint and mismatch stress from neighboring grains in polycrystalline/bulk oxides, the transformation strain of shape memory oxides is relatively small, and micro-cracks can appear after some cycles. However, recent progress in shape memory oxide research related to small-scale approaches such as decreasing the amounts of grain boundaries, strain-engineering, and application in the form of nanoscale thin films shows that some oxides are capable to exhibit excellent shape memory effects and superelasticity at nano/micro-scales. The materials systems ZrO2, BiFO3, and VO2 are discussed with respect to their shape memory performance in bulk and small-scale.
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Shen, Xiao, Yevgeniy S. Puzyrev i Sokrates T. Pantelides. "Vacancy breathing by grain boundaries—a mechanism of memristive switching in polycrystalline oxides". MRS Communications 3, nr 3 (wrzesień 2013): 167–70. http://dx.doi.org/10.1557/mrc.2013.32.
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Merkle, L., i L. J. Thompson. "Atomic Structure of [110] Tilt Grain Boundaries in FCC Materials". Microscopy and Microanalysis 3, S2 (sierpień 1997): 675–76. http://dx.doi.org/10.1017/s1431927600010266.
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High-resolution electron microscopy (HREM) has been used to study the atomic-scale structure and localized relaxations at grain boundaries (GBs) in Au, Al, and MgO. The [110] tilt GBs play an important role in polycrystalline fee metals since among all of the possible GB geometries this series of misorientations as a whole contains the lowest energies, including among others the two lowest energy GBs, the (111) and (113) twins. Therefore, studies of the atomic-scale structure of [110] tilt GBs in fee metals and systematic investigations of their dependence on misorientation and GB plane is of considerable importance to materials science. [110] tilt GBs in ceramic oxides of the fee structure are also of considerable interest, since in this misorientation range polar GBs exist, i.e. GBs in which crystallographic planes that are made up of complete layers of cations or anions can join to form a GB.Thin singlecrystalline films of (110) Au were prepared by vacuum evaporation of Au onto (110) NaCl.
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Lee, Ming Kwei, Chih Feng Yen, Tsung Hsiang Shih, Chen Lia Ho, Hung Chang Lee, Hwai Fu Tu i Cho Han Fan. "Electrical Characteristics of Fluorine Passivated MOCVD-TiO2 Film on (NH4)2Sx Treated GaAs". Key Engineering Materials 368-372 (luty 2008): 232–34. http://dx.doi.org/10.4028/www.scientific.net/kem.368-372.232.
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The high Dit is the major problem of III-V compound semiconductor MOSFET, which causes the pinning of the surface Fermi level near the middle of the energy gap. The GaAs with (NH4)2Sx treatment (S-GaAs) can remove the native oxides on GaAs and prevent it from oxidizing. The electrical characteristics of fluorinated polycrystalline TiO2 films deposited on p-type(100) S-GaAs were investigated. The fluorine from liquid phase deposition solution can passivate the grain boundary of polycrystalline TiO2 prepared by MOCVD. The leakage current through the grain boundaries was suppressed. The leakage current of MOCVD-TiO2/S-GaAs can be improved from 6.8 x 10-6 and 0.2 A/cm2 to 3.41 x 10-7 and 1.13 x 10-6A/cm2 under positive and negative electric fields at 1.5 MV/cm, respectively. Dit and k can be improved from 1.44 x 1012 cm-2eV-1 to 4.6 x 1011 cm-2eV-1 and 52 to 65, respectively. The effective oxide charges can be improved from 2.5 x 1012 C/cm-2 to 9.3 x 1011 C/cm-2.
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Kizuka, T., M. Iijima i N. Tanaka. "Time-resolved high-resolution electron microscopy of grain migration process in MgO films". Proceedings, annual meeting, Electron Microscopy Society of America 54 (11.08.1996): 674–75. http://dx.doi.org/10.1017/s0424820100165835.
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High-resolution electron microscopy (HREM) has been employed intensively to analyze the atomic structures of grain boundaries and interfaces having two dimensional structures inside polycrystalline and composite materials. Furthermore time-resolved HREM (TRHREM) is required to analyze the behavior of grain boundaries and interfaces at atomic scale. The grain boundary migration, which is a typical grain boundary behavior, is a fundamental process relating to structural stability of polycrystalline materials. The mechanism of the migration has been still unknown.In the present study, the variation of atomic arrangement at the grain boundary migration of a MgO [001]Σ5 boundary was analyzed by TRHREM.Magnesium oxide polycrystalline films were prepared by vacuum-deposition on air-cleaved (001) surfaces of sodium chloride at 300°C. TRHREM was carried out at room temperature using a 200-kV electron microscope (JEOL, JEM2010) equipped with a high sensitive TV camera and a video tape recorder. The spatial resolution of the system was 0.2 nm at 200 kV and the time resolution was 1/60 s. Electron beam density was 30 A/cm2.
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Spinella, C., F. Benyaïch, A. Cacciato, E. Rimini, G. Fallico i P. Ward. "Role of grain boundaries in the epitaxial realignment of undoped and As-doped polycrystalline silicon films". Journal of Materials Research 8, nr 10 (październik 1993): 2608–12. http://dx.doi.org/10.1557/jmr.1993.2608.
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The early stages of the thermally induced epitaxial realignment of undoped and As-doped polycrystalline Si films deposited onto crystalline Si substrates were monitored by transmission electron microscopy. Under the effect of the heat treatment, the native oxide film at the poly-Si/c-Si interface begins to agglomerate into spherical beads. The grain boundary terminations at the interface are the preferred sites for the triggering of the realignment transformation which starts by the formation of epitaxial protuberances at these sites. This feature, in conjunction with the microstructure of the films during the first instants of the heat treatment, explains the occurrence of two different realignment modes. In undoped films the epitaxial protuberances, due to the fine grain structure, are closely distributed and grow together forming a rough interface moving toward the film's surface. For As-doped films, the larger grain size leaves a reduced density of realignment sites. Due to As doping some of these sites grow fast and form epitaxial columns that further grow laterally at the expense of the surrounding polycrystalline grains.
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Tietz, L. A., C. B. Carter, D. K. Lathrop, S. E. Russek i R. A. Buhrman. "Special grain boundaries in YBa2Cu3O7-x". Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988): 870–71. http://dx.doi.org/10.1017/s0424820100106417.
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Much attention has recently been paid to the characterization of twin boundaries in YBa2Cu3O7-x (YBCO). However, in polycrystalline samples other high-angle grain boundaries may have a much more significant effect on, not only the superconducting behavior, but also the chemical and mechanical stability of the material. In the present study, attention has therefore also been focussed on several types of low-angle and high-angle grain boundaries. Such boundaries are frequently found in thin films of this material which are grown on {001}-oriented, single-crystal yttria-stabilized zirconia (YSZ) or magnesium oxide by electron beam co-evaporation of the metals in an oxygen atmosphere. The fact that over most of the substrate these films are oriented epitactically with respect to the zirconia substrate means that these high-angle grain boundaries can be characterized in a relatively routine manner using selected-area diffraction. The high-angle boundaries observed in this study include those produced by 23.5°, 29°, and 45° rotations about [001] and 90° rotations about [100] or [010]. These boundaries are compared to special high-angle grain boundaries in cubic materials.
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Lin, Feng. "(Battery Division Early Career Award Sponsored by Neware Technology Limited) Design, Synthesis, and Characterization of Cathode Microstructures in Lithium Batteries". ECS Meeting Abstracts MA2022-02, nr 3 (9.10.2022): 210. http://dx.doi.org/10.1149/ma2022-023210mtgabs.
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The propagation of redox reactions governs the electrochemical properties of battery materials and their critical performance metrics in battery cells. The recent research progress, especially aided by advanced analytical techniques, has revealed that incomplete and heterogeneous redox reactions prevail in many electrode materials. Advanced high-capacity cathode materials are mostly polycrystalline materials that exhibit complex charge distribution (the valence state distribution of the redox-active cations) due to the presence of numerous constituting grains and grain boundaries. The redox reactions in individual grains typically do not proceed concurrently due to their distinct geometric locations in polycrystalline particles. As a result, these unsynchronized local redox events collectively induce heterogeneous and anisotropic charge distribution, building up intergranular and intragranular stress. Therefore, these polycrystalline materials may exhibit weak mechanical stability, leading to undesired chemomechanical breakdown during battery operation. Grain engineering in polycrystalline materials provides a large playground to modulate the materials properties beyond controlling the chemical composition, and electronic and crystal structures. In particular, the anisotropic ion-conducting pathways in layered oxides make the grain crystallographic orientation a critical factor in determining the modality of the redox reactions in these materials. This presentation will discuss our recent progress in the design, synthesis, and characterization of cathode microstructures in lithium batteries. First, we will discuss how the charge distribution is guided by grain crystallographic orientations in polycrystalline battery materials. We elucidate the spatially resolved charge distribution in lithium layered oxides with different grain crystallographic arrangements and establish a model to quantify their charge distributions. While the holistic “surface-to-bulk” charge distribution prevails in polycrystalline particles, the crystallographic orientation-guided redox reaction governs the charge distribution in the local charged nanodomains. Compared to the randomly oriented grains, the radially aligned grains exhibit a lower cell polarization and higher capacity retention upon battery cycling. The radially aligned grains create less tortuous lithium-ion pathways, thus improving the charge homogeneity as statistically quantified from over 20 million nanodomains in polycrystalline particles. This study provides an improved understanding of the charge distribution and chemomechanical properties of polycrystalline battery materials. Second, we will discuss how the grain arrangement affects the thermal stability of polycrystalline cathode materials in rechargeable batteries. We performed a systematic in situ study on the Ni-rich polycrystalline cathode materials to investigate the fundamental degradation mechanism of charged cathodes at elevated temperatures, which is essential for tailoring material properties and improving performance. Using multiple microscopy, scattering, thermal, and electrochemical probes, we decoupled the major contributors to the thermal instability from intertwined factors. Based on our findings, the cathode grain microstructure has a forgotten yet important role in the thermal stability of polycrystalline rechargeable batteries. Oxygen release, as an important process during the thermal runaway, can be regulated through engineering grain arrangements. The grain arrangement can modulate the macroscopic crystallographic transformation pattern and oxygen diffusion length in layered cathodes to offer more possibilities for cathode material design and synthesis. Third, we will discuss our new understanding of particle behaviors in composite cathodes. We capture and quantify the particle motion during the solidification of battery electrodes and reveal the statistics of the dynamically evolving motion in the drying process, which has been challenging to resolve. We discover that the particle motion exhibits a strong dependence on its geometric location within a drying electrode. Our results also imply that the final electrode quality can be controlled by balancing the solvent evaporation rate and the particle mobility in the region close to the drying surface. We formulate a network evolution model to interpret the regulation and equilibration between electrochemical activity and mechanical damage of these particles. Through statistical analysis of thousands of particles using x-ray phase-contrast holotomography in a Ni-rich cathode, we found that the local network heterogeneity results in asynchronous activities in the early cycles, and subsequently the particle assemblies move toward a synchronous behavior. Our study pinpoints the chemomechanical behavior of individual particles and enables better designs of the conductive network to optimize the utility of all the particles during operation.
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Babcock, Susan E. "High-Temperature Superconductors from the Grain Boundary Perspective". MRS Bulletin 17, nr 8 (sierpień 1992): 20–26. http://dx.doi.org/10.1557/s0883769400041816.
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The high-transition-temperature superconductors (HTS) present a number of challenging materials science problems whose solutions must precede their use in applications. This article offers a view on our collective progress toward resolution of one central HTS issue, the “weak-link” character of high-angle grain boundaries.Why Are HTS Grain Boundaries of Such Interest?The properties of high-angle grain boundaries control the macroscopic electromagnetic character of all superconducting copper oxides that are produced in polycrystalline form. In particular, grain boundaries limit the transport critical current density (Jct) and determine its dependence on applied magnetic field (H) and temperature (T). Jct is the maximum macroscopic current density that the superconductor can support in the nondissipative state. H and T are the two most important environmental variables for applications of superconductivity. Thus, the Jct(H, T) characteristic largely dictates the types of applications for which a superconducting material can be used successfully.High-angle grain boundaries are the immediate obstacle to further development of materials for applications that require large Jct values in high magnetic fields. The problem arises because most high-angle grain boundaries act like Josephson-coupled weak links. The characteristic properties of such junctions are a reduced zero-field Jct value and, more importantly, a strongly magnetic-field-dependent Jct that can decrease by more than an order of magnitude in even weak fields of a few millitesla (Fig. 1). Such Jct(H) characteristics are clearly a very serious problem for high-field magnet applications such as motors, generators, energy storage systems, and MRI machines.
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Kizuka, T., i N. Tanaka. "Time-resolved high-resolution electron microscopy of structural transformation in nanocrystalline ZnO films". Proceedings, annual meeting, Electron Microscopy Society of America 54 (11.08.1996): 978–79. http://dx.doi.org/10.1017/s0424820100167354.
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Mechanical properties of polycrystalline materials become anomalous when the grain size and grain boundary length decrease to nanometer scale. For example, ductility and toughness increase significantly in nanometer-grained ceramics (nanocrystalline ceramics). Ductility increases due to appearance of fine-grained-superplastic deformation. Grain boundary migration and interface migration are fundamental processes of the superplastic deformation. Structural transformation of fine grains is a factor which limits the toughness in polycrystalline ceramics because the transformation relaxes internal strain. The behavior of grain boundaries and interfaces, such as diffusion bonding and Czochralski-type crystal growth at ambient temperature, can be analyzed by a time-resolved high-resolution electron microscopy (TRHREM) developed by Kizuka et al.,In the present study, grain boundary migration and successive transformation of crystal structure in nanocrystalline ZnO were investigated by TRHREM.Zinc oxide was vacuum-deposited on air-cleaved (001) surfaces of sodium chloride at 200°C. TRHREM was carried out at room temperature using a 200-kV electron microscope (JEOL, JEM2010) equipped with a high sensitive TV camera and a video tape recorder.
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Moriyama, Takumi, Takahiro Yamasaki, Takahisa Ohno, Satoru Kishida i Kentaro Kinoshita. "Formation Mechanism of Conducting Path in Resistive Random Access Memory by First Principles Calculation Using Practical Model Based on Experimental Results". MRS Advances 1, nr 49 (2016): 3367–72. http://dx.doi.org/10.1557/adv.2016.461.
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ABSTRACTFor practical use of Resistive Random Access Memory (ReRAM), understanding resistive switching mechanism in transition metal oxides (TMO) is important. Some papers predict its mechanism by using first principles calculation; for example, TMO become conductive by introducing oxygen vacancy in bulk single crystalline TMO. However, most of ReRAM samples have polycrystalline structures. In this paper, we introduced a periodic slab model to depict grain boundary and calculated the surface energy and density of states for surfaces of NiO with various orientations using first-principles calculation to consider the effect of grain boundaries for resistive switching mechanisms of ReRAM. As a results, vacancies can be formed on the side surface of grain more easily than in grain. Moreover, we showed that surface conductivity depends on surface orientation of NiO and the orientation of side surface of grain can change easily by introduction of vacancies, which is the switching mechanism of NiO-ReRAM
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Yen, H., E. P. Kvam, R. Bashir, S. Venkatesan i G. W. Neudeck. "Interface morphology of thermal oxide grown on polycrystalline silicon by different processes". Proceedings, annual meeting, Electron Microscopy Society of America 50, nr 2 (sierpień 1992): 1396–97. http://dx.doi.org/10.1017/s0424820100131619.
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Polycrystalline silicon, when highly doped, is commonly used in microelectronics applications such as gates and interconnects. The packing density of integrated circuits can be enhanced by fabricating multilevel polycrystalline silicon films separated by insulating SiO2 layers. It has been found that device performance and electrical properties are strongly affected by the interface morphology between polycrystalline silicon and SiO2. As a thermal oxide layer is grown, the poly silicon is consumed, and there is a volume expansion of the oxide relative to the atomic silicon. Roughness at the poly silicon/thermal oxide interface can be severely deleterious due to stresses induced by the volume change during oxidation. Further, grain orientations and grain boundaries may alter oxidation kinetics, which will also affect roughness, and thus stress.Three groups of polycrystalline silicon films were deposited by LPCVD after growing thermal oxide on p-type wafers. The films were doped with phosphorus or arsenic by three different methods.
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Hou, Ming-Dong, Xiang-Wen Zhou, Malin Liu i Bing Liu. "Molecular Dynamics Simulation of High Temperature Mechanical Properties of Nano-Polycrystalline Beryllium Oxide and Relevant Experimental Verification". Energies 16, nr 13 (25.06.2023): 4927. http://dx.doi.org/10.3390/en16134927.
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This article investigated the deformation behavior of nano-polycrystalline beryllium oxide under tensile and compressive stress using the molecular dynamics simulation method. Both the tensile and compressive test results indicate that beryllium oxide breaks mainly along grain boundaries. At low temperature, there is little internal deformation of beryllium oxide grains. When the temperature is above 1473 K, the internal deformation of beryllium oxide grains also occurs, and the phenomenon becomes more obvious with the increase in temperature. This deformation within the grain should be plastic. The flexural strength fracture morphology of beryllium oxide also shows that the fracture mode of beryllium oxide is a brittle fracture at low temperature, while the slip bands appear at 1773 K. This indicates that beryllium oxide, as a ceramic material, can also undergo plastic deformation under high temperature and stress.
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Idczak, Rafał, Karolina Idczak i Robert Konieczny. "Corrosion of Polycrystalline Fe-Si Alloys Studied by TMS, CEMS, and XPS". Corrosion 74, nr 6 (7.01.2018): 623–34. http://dx.doi.org/10.5006/2676.
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The high-temperature corrosion behavior of three polycrystalline Fe-Si alloys containing approximately 4, 5, and 10 at% Si was studied using transmission Mössbauer spectroscopy (TMS), conversion electron Mössbauer spectroscopy (CEMS), and x-ray photoelectron spectroscopy (XPS). The XPS measurements reveal the strong segregation process of silicon atoms to the surface. Moreover, the obtained XPS results suggest that the presence of adsorbed oxygen on the Fe-Si surface effectively enhances the silicon segregation process. On the other hand, the obtained TMS and CEMS spectra show that even 10% of silicon atoms dissolved in the iron matrix do not prevent high-temperature corrosion of the studied Fe-Si alloys. During exposure to air at 870 K, a systematic growth of an α-Fe2O3 compound was observed. Finally, the Mössbauer results show that, during exposure to air, oxygen atoms diffuse to the studied polycrystalline materials not only through the oxide/metal interface on the surface but also along the grain boundaries. Such effects result in the formation of iron oxides in deeper parts of the alloy.
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Kim, Sang-il, Jiwoo An, Woo-Jae Lee, Se Kwon, Woo Nam, Nguyen Du, Jong-Min Oh, Sang-Mo Koo, Jung Cho i Weon Shin. "Effect of ZnO and SnO2 Nanolayers at Grain Boundaries on Thermoelectric Properties of Polycrystalline Skutterudites". Nanomaterials 10, nr 11 (16.11.2020): 2270. http://dx.doi.org/10.3390/nano10112270.
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Nanostructuring is considered one of the key approaches to achieve highly efficient thermoelectric alloys by reducing thermal conductivity. In this study, we investigated the effect of oxide (ZnO and SnO2) nanolayers at the grain boundaries of polycrystalline In0.2Yb0.1Co4Sb12 skutterudites on their electrical and thermal transport properties. Skutterudite powders with oxide nanolayers were prepared by atomic layer deposition method, and the number of deposition cycles was varied to control the coating thickness. The coated powders were consolidated by spark plasma sintering. With increasing number of deposition cycle, the electrical conductivity gradually decreased, while the Seebeck coefficient changed insignificantly; this indicates that the carrier mobility decreased due to the oxide nanolayers. In contrast, the lattice thermal conductivity increased with an increase in the number of deposition cycles, demonstrating the reduction in phonon scattering by grain boundaries owing to the oxide nanolayers. Thus, we could easily control the thermoelectric properties of skutterudite materials through adjusting the oxide nanolayer by atomic layer deposition method.
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Brydson, Rik, Peter C. Twigg, Fiona Loughran i Frank L. Riley. "Influence of CaO–SiO2 ratio on the chemistry of intergranular films in liquid-phase sintered alumina and implications for rate of erosive wear". Journal of Materials Research 16, nr 3 (marzec 2001): 652–65. http://dx.doi.org/10.1557/jmr.2001.0120.
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Polycrystalline aluminas sintered with 10 wt% additions of calcium oxide (CaO) and silica (SiO2) in varying molar ratios were fabricated via precipitation, calcination, and hot pressing. Alumina microstructures were analyzed by scanning electron microscopy in terms of their mean grain size, grain size distribution, and grain aspect ratios. High-resolution transmission electron microscopy (HRTEM) showed the presence of an amorphous intergranular glassy phase at two- and three-grain boundaries. The intergranular film width at two-grain boundaries, determined by HRTEM, appeared to vary with the [CaO]:[SiO2] ratio of the additive as did the chemical composition and local chemistry, determined by high-resolution analytical transmission electron microscopy and scanning transmission electron microscopy (using both energy dispersive x-ray and electron energy loss spectroscopy). The factors influencing the erosive wear rate are discussed including the chemistry and associated fracture energy of the intergranular glassy film. Wet erosive wear rates of the densified materials were determined and had a strong dependence on the [CaO]:[SiO2] ratio in the additive.
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Lin, H., i D. P. Pope. "Slip traces caused by plastic deformation during recrystallization of thin metal sheets". Proceedings, annual meeting, Electron Microscopy Society of America 52 (1994): 620–21. http://dx.doi.org/10.1017/s0424820100170839.
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During a study of mechanical properties of recrystallized B-free Ni3Al single crystals, regularly spaced parallel traces within individual grains were discovered on the surfaces of thin recrystallized sheets, see Fig. 1. They appeared to be slip traces, but since we could not find similar observations in the literature, a series of experiments was performed to identify them. We will refer to them “traces”, because they contain some, if not all, of the properties of slip traces. A variety of techniques, including the Electron Backscattering Pattern (EBSP) method, was used to ascertain the composition, geometry, and crystallography of these traces. The effect of sample thickness on their formation was also investigated.In summary, these traces on the surface of recrystallized Ni3Al have the following properties:1.The chemistry and crystallographic orientation of the traces are the same as the bulk. No oxides or other second phases were observed.2.The traces are not grooves caused by thermal etching at previous locations of grain boundaries.3.The traces form after recrystallization (because the starting Ni3Al is a single crystal).4.For thicknesses between 50 μm and 720 μm, the density of the traces increases as the sample thickness decreases. Only one set of “protrusion-like” traces is visible in a given grain on the thicker samples, but multiple sets of “cliff-like” traces are visible on the thinner ones (See Fig. 1 and Fig. 2).5.They are linear and parallel to the traces of {111} planes on the surface, see Fig. 3.6.Some of the traces terminate within the interior of the grains, and the rest of them either terminate at or are continuous across grain boundaries. The portion of latter increases with decreasing thickness.7.The grain size decreases with decreasing thickness, the decrease is more pronounced when the grain size is comparable with the thickness, Fig. 4.8.Traces also formed during the recrystallization of cold-rolled polycrystalline Cu thin sheets, Fig. 5.
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Tian, Yingyi, Shuanhu Wang, Xiangyang Wei, Ruishu Yang i Kexin Jin. "Anomalous Hall effect superimposed in polycrystalline SrRuO3 thick film". Applied Physics Letters 120, nr 14 (4.04.2022): 142404. http://dx.doi.org/10.1063/5.0085391.
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The electric, magnetic, and thermal properties of transition metal oxide films can be modulated by introducing polycrystalline at the macroscopic grain boundaries. Based on these points, in this work, we studied the two-channel anomalous Hall effect (AHE) in polycrystalline ferromagnetic SrRuO3 (SRO) films. The magnetic regions with different crystal directions have different coercivities, resulting in two opposite AHE channels in the polycrystalline SRO layer. However, single-crystal SRO films prepared under the same conditions are found to exhibit only one AHE. The superposition of the two AHE leads to the hump-like behavior of the Hall resistance loop, which is caused by the change of crystalline. This observation provides a new way to explain the hump-like feature of SRO.
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Marcus, Philippe, i Vincent Maurice. "Atomic level characterization in corrosion studies". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2098 (12.06.2017): 20160414. http://dx.doi.org/10.1098/rsta.2016.0414.
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Atomic level characterization brings fundamental insight into the mechanisms of self-protection against corrosion of metals and alloys by oxide passive films and into how localized corrosion is initiated on passivated metal surfaces. This is illustrated in this overview with selected data obtained at the subnanometre, i.e. atomic or molecular, scale and also at the nanometre scale on single-crystal copper, nickel, chromium and stainless steel surfaces passivated in well-controlled conditions and analysed in situ and/or ex situ by scanning tunnelling microscopy/spectroscopy and atomic force microscopy. A selected example of corrosion modelling by ab initio density functional theory is also presented. The discussed aspects include the surface reconstruction induced by hydroxide adsorption and formation of two-dimensional (hydr)oxide precursors, the atomic structure, orientation and surface hydroxylation of three-dimensional ultrathin oxide passive films, the effect of grain boundaries in polycrystalline passive films acting as preferential sites of passivity breakdown, the differences in local electronic properties measured at grain boundaries of passive films and the role of step edges at the exposed surface of oxide grains on the dissolution of the passive film. This article is part of the themed issue ‘The challenges of hydrogen and metals’.
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McKenna, Keith P., i Alexander L. Shluger. "Electron and hole trapping in polycrystalline metal oxide materials". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 467, nr 2131 (9.02.2011): 2043–53. http://dx.doi.org/10.1098/rspa.2010.0518.
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Electron and hole trapping by grain boundaries and dislocations in polycrystalline materials is important for wide ranging technological applications such as solar cells, microelectronics, photo-catalysts and rechargeable batteries. In this article, we first give an overview of the computational and methodological challenges involved in modelling such effects. This is followed by a discussion of two recent studies we have made on electron/hole trapping in wide gap insulators. The results suggest that such effects can be important for many applications which we discuss. These computationally demanding calculations have made extensive use of both the HPCx and HECToR services.
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Solórzano, I. G., J. B. Vander Sande, K. K. Baek i H. L. Tuller. "A high-resolution EM study of grain boundaries in Pr and Co-doped ZnO ceramics". Proceedings, annual meeting, Electron Microscopy Society of America 51 (1.08.1993): 1150–51. http://dx.doi.org/10.1017/s0424820100151581.
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Metal oxide varistors are multijunction materials whose nonlinear current-voltage characteristics derive from the electrical activity of their grain boundary regions. The high degree of nonlinear-ity in polycrystalline ZnO has been attributed to the synergistic action of two types of cations added in sufficient concentrations: transition metals, such as Co and Mn which have ionic radii similar to that of the ZnO matrix, and dopants with large ionic radii, such as Bi and Pr which segregate at grain boundaries and usually form intergranular phases. The present investigation was undertaken with the objective to clarify the role of dopants in an electrically active Pr and Co doped ZnO ceramic by studying the structure and chemistry of individual grain boundaries through high-resolution electron microscopy (HREM) and analytical electron microscopy (AEM).Bulk specimens containing 1 mol% Pr and 1 mol% Co were prepared by conventional sintering at 1400° C. Some samples followed an oxidative anneal at 650° C for 3 h to further enhance their electrical activity.
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Li, Hua Long, Jianlong Lin i Jerzy A. Szpunar. "Software for Simulation of Oxidation Processes". Defect and Diffusion Forum 237-240 (kwiecień 2005): 189–94. http://dx.doi.org/10.4028/www.scientific.net/ddf.237-240.189.
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A methodology for discrete simulation has been developed that incorporates many structural characteristics of polycrystalline material properties, such as: texture, grain boundaries, microstructure, phase composition, chemical composition, stored energy, and residual stresses. The computer models that have been developed to study oxidation processes are based on a quantitative description of the oxide and substrate structure. That description allows for the simulation of the transport of metal and oxygen ions along interfaces and bulk portions of material and the formation of oxide structure. The proposed model can help researchers and engineers to understand the physical mechanism of oxidation in order to predict material behavior and optimize material processing and properties. In this paper, the results on the simulation of the oxidation process are presented on different substrates of Zr-Nb alloys, which are used for the manufacturing the pressure tubes used in the CANDU nuclear reactors. The effects of substrate texture, microstructure, grain boundaries, and beta phase distribution on oxidation kinetics and hydrogen permeation are demonstrated.
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Zhang, Jingdan, Xiaolin Li, Yawei Lei, Yange Zhang, Xiangyan Li, Yichun Xu, Xuebang Wu, Junfeng Yang, Bingsheng Li i Changsong Liu. "Effects of Alloying Elements on the Solution and Diffusion of Oxygen at Iron Grain Boundary Investigated by First-Principles Study". Metals 13, nr 4 (17.04.2023): 789. http://dx.doi.org/10.3390/met13040789.
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The effects of alloying elements (Si, Cr, Mo) on the solution and diffusion of oxygen (O) atoms at the grain boundary of iron (Fe) Σ5(310)/[001] are investigated by the simulations of ab initio density functional theory (DFT). It is found that Si, Mo and Cr prefer to segregate to the grain boundary, and further affect the solution and diffusion of O atoms at Fe grain boundaries. The segregated Cr promotes the solution of O, while Si and Mo inhibit the solution of O at the grain boundary. Meanwhile, Cr and Si accelerate the diffusion of O, and Mo retards the diffusion of O in the grain boundary. Further analysis indicates that the effects are closely related to the interactions between the alloying elements and O atoms, which are determined by the competition between the distortion of local structure and the charge transfer between local atoms. Finally, the effects of alloying elements on the O concentration distribution near the grain boundary are explored by employing the Langmuir–McLean models. This work not only provides insights into the effects of alloying elements on the solution and diffusion of O at grain boundaries, but also provides parameters of the atomic interactions for the initial oxidation simulation on a large scale, which relates to the growth of oxide in polycrystalline systems with various grain sizes at experimental temperatures.
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Ou, Limin, Shengheng Nong, Ruoxi Yang, Yaoying Li, Jinrong Tao, Pan Zhang, Haifu Huang i in. "Multi-Role Surface Modification of Single-Crystalline Nickel-Rich Lithium Nickel Cobalt Manganese Oxides Cathodes with WO3 to Improve Performance for Lithium-Ion Batteries". Nanomaterials 12, nr 8 (12.04.2022): 1324. http://dx.doi.org/10.3390/nano12081324.
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Compared with the polycrystalline system, the single-crystalline ternary cathode material has better cycle stability because the only primary particles without grain boundaries effectively alleviate the formation of micro/nanocracks and retain better structural integrity. Therefore, it has received extensive research attention. There is no consistent result whether tungsten oxide acts as doping and/or coating from the surface modification of the polycrystalline system. Meanwhile, there is no report on the surface modification of the single-crystalline system by tungsten oxide. In this paper, multirole surface modification of single-crystalline nickel-rich ternary cathode material LiNi0.6Co0.2Mn0.2O2 by WO3 is studied by a simple method of adding WO3 followed by calcination. The results show that with the change in the amount of WO3 added, single-crystalline nickel-rich ternary cathode material can be separately doped, separately coated, and both doped and coated. Either doping or coating effectively enhances the structural stability, reduces the polarization of the material, and improves the lithium-ion diffusion kinetics, thus improving the cycle stability and rate performance of the battery. Interestingly, both doping and coating (for SC-NCM622-0.5%WO3) do not show a more excellent synergistic effect, while the single coating (for SC-NCM622-1.0%WO3) after eliminating the rock-salt phase layer performs the most excellent modification effect.
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Lespiaux, Justine, Fabien Deprat, Jérémy Vives, Romain Duru, Mehmet Bicer, Alexis Gauthier, Edoardo Brezza i in. "Reduced Pressure – Chemical Vapor Deposition of Monocrystalline and Polycrystalline Si(:B) and SiGe(:B) Layers on Blanket Wafers". ECS Transactions 109, nr 4 (30.09.2022): 217–36. http://dx.doi.org/10.1149/10904.0217ecst.
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In this paper, epitaxial growths or depositions were performed, in 300 mm RP-CVD chambers, on two types of templates: N-type Si substrates or poly-Si/oxide/ P-type Si substrates. SiH4+HCl+H2 and SiH2Cl2+HCl+GeH4+H2 chemistries were used to deposit Si and SiGe layers between 675-750°C and 10-20 Torr on such wafers. Monocrystalline and polycrystalline growth kinetics were similar for intrinsic SiGe. Meanwhile, growth kinetics and boron incorporation were different for mono-Si:B, mono-SiGe:B, poly-Si:B and poly-SiGe:B layers. While the impact of B atoms is well documented in monocrystalline layers, it is still poorly understood for polycrystalline layers. An attempt has therefore been made to quantify it by measuring the poly-structure, with a focus on the poly-grains size and the number of grain boundaries. A lattice contraction coefficient β = - 9.82 * 10-24 cm3 has otherwise been extracted from an in-depth study of the incorporation of B atoms into substitutional sites of the SiGe epitaxial lattice.
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Ramamurthy, Sundar, Brian C. Hebert i C. Barry Carter. "Olivine-MgO interfaces produced by crystallization of glass fulms on single-crystal MgO substrates". Proceedings, annual meeting, Electron Microscopy Society of America 53 (13.08.1995): 342–43. http://dx.doi.org/10.1017/s0424820100138087.
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Glassy silicates are present at grain boundaries in almost all liquid-phase sintered ceramic oxides. In many cases, the amorphous-crystalline interfaces in the sintered microstructure can be modified by inducing crystallization of the glassy phase. The intergranular phases in polycrystalline MgO are typically silicates with cations of calcium, magnesium and iron in the silicate network. A systematic approach to study the crystallization behavior of glass-MgO interfaces has been attempted in the present study. Following the work by Mallamaci in which crystallization of a silicate glass in contact with A12O3 was studied, devitrification of glass in contact with single-crystal MgO has been investigated. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the resulting microstructures.A pellet of Mg2SiO4 (forsterite) prepared by hot-pressing MgO and SiO2 powders was used as the target for depositing glass films onto single-crystal MgO substrates by pulsed-laser deposition (PLD). Glass films with the composition of olivine.
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Jaseliunaite, Justina, i Arvaidas Galdikas. "Kinetic Modeling of Grain Boundary Diffusion: The Influence of Grain Size and Surface Processes". Materials 13, nr 5 (26.02.2020): 1051. http://dx.doi.org/10.3390/ma13051051.
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Based on rate equations, the kinetics of atom adsorption, desorption, and diffusion in polycrystalline materials is analyzed in order to understand the influence of grain boundaries and grain size. The boundary conditions of the proposed model correspond with the real situation in the electrolytes of solid oxide hydrogen fuel cells (SOFC). The role of the ratio of grain boundary and grain diffusion coefficients in perpendicular and parallel (to the surface) concentration profiles is investigated. In order to show the influence of absolute values of grain and grain boundary diffusion coefficients, we select four different cases in which one of the diffusion coefficients is kept constant while the others vary. The influence of grain size on diffusion processes is investigated using different geometrical models. The impact of kinetic processes taking place on the surface is analyzed by comparing results obtained assuming the first layer as a constant source and then involving in the model the processes of adsorption and desorption. It is shown that surface processes have a significant influence on the depth distribution of diffusing atoms and cannot be ignored. The analytical function of overall concentration dependence on grain and grain boundary volume ratio (Vg/Vgb) is found. The solution suggests that the concentration increases as a complementary error function while Vg/Vgb decreases.
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Mary, A. Jacquiline Regina, i S. Arumugam. "Structural and Optical Studies of Molarity Based ZnO Thin Films". Nano Hybrids and Composites 17 (sierpień 2017): 140–48. http://dx.doi.org/10.4028/www.scientific.net/nhc.17.140.
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Zinc Oxide thin films were prepared for different precursor solution molarities from 0.025M to 0.1M by spray pyrolysis deposition technique. A comprehensive study was carried out to realize the effect of concentration of precursor on ZnO thin films. The optimized temperature of the glass substrate was 300°C. From the XRD data it is inferred that the films are polycrystalline and hexagonal wurtzite structure . The degree of preferred orientation were along diffraction planes (100), (002) and (101) for all the ZnO films. The intensity of the diffraction peak prepared with 0.1M concentration is higher than those prepared at lower concentrations. The grain size (D) was calculated using Debye-Scherrer formula. It was found that the average grain size increases, when the molar concentration increases. As the solution concentration increases, the band gap decreases. The films are transparent in the visible region (85%), and the transmittance decreases as the molar concentration increases, which is caused by optical scattering at grain boundaries.
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Wang, Anchuan, Nikki L. Edleman, Jason R. Babcock, Tobin J. Marks, Melissa A. Lane, Paul R. Brazis i Carl R. Kannewurf. "Growth, microstructure, charge transport, and transparency of random polycrystalline and heteroepitaxial metalorganic chemical vapor deposition-derived gallium–indium–oxide thin films". Journal of Materials Research 17, nr 12 (grudzień 2002): 3155–62. http://dx.doi.org/10.1557/jmr.2002.0456.
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Gallium–indium–oxide films (GaxIn2⊟xO3), where x = 0.0–1.1, were grown by low-pressure metalorganic chemical vapor deposition using the volatile metalorganic precursors In(dpm)3 and Ga(dpm)3 (dpm = 2,2,6,6-tetramethyl-3,5-heptanedionato). The films were smooth (root mean square roughness = 50–65 Å) with a homogeneously Ga-substituted, cubic In2O3 microstructure, randomly oriented on quartz or heteroepitaxial on (100) yttria-stabilized zirconia single-crystal substrates. The highest conductivity of the as-grown films was found at x = 0.12, with σ = 700 S/cm [n-type; carrier density = 8.1 × 1019 cm⊟3; mobility = 55.2 cm2/(V s); dσ/dT<0]. The optical transmission window of such films is considerably broader than that of Sn-doped In2O3, and the absolute transparency rival or exceeds that of the most transparent conductive oxides known. Reductive annealing, carried out at 400–425 C° in a flowing gas mixture of H2 (4%) and N2, resulted in increased conductivity (σ 1400 S/cm; n-type), carrier density (1.4 × 1020 cm⊟3), and mobility as high as 64.6 cm2/(V s), with little loss in optical transparency. No significant difference in carrier mobility or conductivity is observed between randomly oriented and heteroepitaxial films, arguing in combination with other data that carrier scattering effects at high-angle grain/domain boundaries play a minor role in the conductivity mechanism.
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Xu, Xu, Zeping Zhang i Wenjuan Yao. "Mechanical Properties of Graphene Oxide Coupled by Multi-Physical Field: Grain Boundaries and Functional Groups". Crystals 11, nr 1 (14.01.2021): 62. http://dx.doi.org/10.3390/cryst11010062.
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Graphene and graphene oxide (GO) usually have grain boundaries (GBs) in the process of synthesis and preparation. Here, we “attach” GBs into GO, a new molecular configuration i.e., polycrystalline graphene oxide (PGO) is proposed. This paper aims to provide an insight into the stability and mechanical properties of PGO by using the molecular dynamics method. For this purpose, the “bottom-up” multi-structure-spatial design performance of PGO and the physical mechanism associated with the spatial structure in mixed dimensions (combination of sp2 and sp3) were studied. Also, the effect of defect coupling (GBs and functional groups) on the mechanical properties was revealed. Our results demonstrate that the existence of the GBs reduces the mechanical properties of PGO and show an “induction” role during the tensile fracture process. The presence of functional groups converts in-plane sp2 carbon atoms into out-of-plane sp3 hybrid carbons, causing uneven stress distribution. Moreover, the mechanical characteristics of PGO are very sensitive to the oxygen content of functional groups, which decrease with the increase of oxygen content. The weakening degree of epoxy groups is slightly greater than that of hydroxyl groups. Finally, we find that the mechanical properties of PGO will fall to the lowest values due to the defect coupling amplification mechanism when the functional groups are distributed at GBs.
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Lombos, B. A. "Deep levels in semiconductors". Canadian Journal of Chemistry 63, nr 7 (1.07.1985): 1666–71. http://dx.doi.org/10.1139/v85-279.
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The role of deep-lying trapping centers in semi-insulating GaAs, polysilicon and polycrystalline tin oxide transparent electrode has been systematically investigated. It was demonstrated that some of the peculiar transport properties of these semiconductors can be elucidated by deep level compensation. A multilevel model is presented to determine the position of the Fermi level as a function of impurity concentrations. These include, quantitatively, the deep-lying levels which have been introduced by doping in the case of GaAs and by grain boundaries in the case of polycrystalline films. In the latter cases the dangling bonds, associated to lattice defects, are characterized by energy levels which are localized in the energy gap. These dangling bonds can act as electron traps when empty and hole traps when occupied. These are the deep levels.In each of the investigated three cases, this concept permitted the elucidation of some of the transport properties of these semiconductors.
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Wang, Lei, Yanwei Ma, Qingxiao Wang, Kun Li, Xixiang Zhang, Yanpeng Qi, Zhaoshun Gao i in. "Direct observation of nanometer-scale amorphous layers and oxide crystallites at grain boundaries in polycrystalline Sr1−xKxFe2As2 superconductors". Applied Physics Letters 98, nr 22 (30.05.2011): 222504. http://dx.doi.org/10.1063/1.3592580.
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Kimura, Mutsumi, Tsukasa Eguchi, Satoshi Inoue i Tatsuya Shimoda. "Device Simulation of Grain Boundaries with Oxide-Silicon Interface Roughness in Laser-Crystallized Polycrystalline Silicon Thin-Film Transistors". Japanese Journal of Applied Physics 39, Part 2, No. 8A (1.08.2000): L775—L778. http://dx.doi.org/10.1143/jjap.39.l775.
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Nalivaiko, Oleg Yu, Arcady S. Turtsevich, Vladimir I. Plebanovich i Peter I. Gaiduk. "Segregation-induced formation of Ge nanocrystals in silicon oxide". Journal of the Belarusian State University. Physics, nr 2 (15.06.2022): 70–78. http://dx.doi.org/10.33581/2520-2243-2022-2-70-78.
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The investigation of initial stage of Si1 – xGex alloy deposition and clarification of Ge nanocrystal formation mechanism has been carried out. It was found that at the initial stages of growing layers of Si1 – xGex alloys, the density of island nuclei Si1 – xGex increases by a factor of 2.5–3.4 compared to the density of polycrystalline silicon islands (from 1.07 ⋅ 1011 to 1.90 ⋅ 1011 cm–2 and from 3.1 ⋅ 1010 to 4.3 ⋅ 1010 cm–2 respectively). A decrease in the thickness of the layer corresponding to the end of the induction period and the formation of a continuous Si1 – xGex layer to 8–10 nm (for polycrystalline silicon, the thickness of a similar layer is approximately 22 nm) has been established. It is shown that the Ge nanocrystal formation is occurred by segregationist pushback of Ge atoms by the SiO2 /Si1 – xGex oxidation front and oxidation through grain boundaries during oxidation of Si1 – xGex thin layers, produced by chemical vapor deposition. The MOS structure with array of Ge nanocrystal, which has the hysteresis capacitance characteristics of 1.7–1.8 V and leakage current density from 1.5 ⋅ 10–16 to 2.2 ⋅ 10–16 A/µm2 was obtained.
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Xu, Xu, Chaoqi Xiong, Shaoping Mao i Wenjuan Yao. "Established Model on Polycrystalline Graphene Oxide and Analysis of Mechanical Characteristic". Crystals 12, nr 3 (12.03.2022): 382. http://dx.doi.org/10.3390/cryst12030382.
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It may cause more novel physical effects that the combination with in-plane defects induced by grain boundaries (GBs) and quasi three-dimensional system induced by oxidation functional group. Different from those in blocks, these new physical effects play a significant role in the mechanical properties and transport behavior. Based on the configuration design, we investigate the in-plane and out-plane geometric deformation caused by the coupling of GBs and oxygen-containing functional groups and establish a mechanical model for the optimal design of the target spatial structure. The results show that the strain rate remarkably affect the tensile properties of polycrystalline graphene oxide (PGO). Under high oxygen content (R = 50%), with the increasing strain rate, the PGO is much closer to ductile fracture, and the ultimate strain and stress will correspondingly grow. The growth of temperature reduces the ultimate stress of PGO, but the ultimate strain remains constant. When the functional groups are distributed at the edge of the GBs, the overall strength decreases the most, followed by the distribution on the GBs. Meanwhile, the strength of PGO reaches the greatest value when the functional groups are distributed away from the GBs.
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Cao, Qing. "(Invited) Two-Dimensional Amorphous Carbon Prepared from Solution Precursor As Novel Dielectrics for Nanoelectronics". ECS Meeting Abstracts MA2022-01, nr 9 (7.07.2022): 755. http://dx.doi.org/10.1149/ma2022-019755mtgabs.
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Low-dimensional electronic materials such as carbon nanotubes, graphene, and transition-metal chalcogenides have drawn a lot of interest from the aspects of both fundamental studies and practical applications. Their atomic-scale thickness and unique electrical properties make them become promising candidates as the drop-in replacement of conventional bulk electronic materials in future electronic devices to enable better performance and enhanced functionality. Research on low-dimensional electronic materials so far has predominantly focused on crystalline semimetals and semiconductors. However, advanced electronic devices also require suitable low-dimensional insulators, which are ideally in the highly disordered amorphous form, similar as SiO2 for silicon, to avoid the nonuniformity and defects related with grain boundaries, in order to fulfill their potentials. Here we present a new strategy for the solution-based preparation of atomically thin amorphous carbon as a novel 2D insulator. Our unique process can precisely control the film thickness at atomic level and has excellent scalability toward wafer-scale deposition. The obtained 2D amorphous carbon monolayer exhibits mechanical robustness comparable to graphene and can be suspended as a free-standing membrane on transmission-electron-microscopy grid, allowing the structural characterization down to atomic resolution. The structure-property relationship for such amorphous materials at 2D limit was then established based on a combination of experiment and density-functional theory simulation. The unique physical properties of 2D amorphous carbon suggest it as a promising candidate to accompany crystalline low-dimensional semiconductors and semimetals in future nanoelectronic devices, and its performance advantages over conventional 3D metal oxides and polycrystalline 2D insulators were verified in experiment : Serving as the gate dielectric in graphene transistors, the absence of grain boundaries in 2D amorphous carbon allows us to aggressively reduce the gate-dielectric thickness down to merely three-atomic layers to enhance the capacitance coupling between the gate and the channel, while still maintaining a low leakage current density below 10-4 A/cm2, which is many orders of magnitude lower compared to the leakage current across the polycrystalline hexagonal boron nitride with the same thickness. Meanwhile, the perfectly clean van der Waals interface it forms with the graphene channel leads to the sharply reduction of the device hysteresis and thus average effective mobility twice as high as that of devices built with bulk SiO2 as gate dielectric. Serving as the switching medium in resistive random access memory cells, the atomic-level thinness of the 2D amorphous carbon enables low operating voltage below 0.4 V, fast switching time <20 ns, and low energy consumption per write operation below 20 fJ, together with excellent endurance (>104) and data retention (>10 years @ 85oC). Moreover, its atomic structural heterogeneity provides well defined ion-transport pathways as suggested in ab initio simulations, leading to the drastically improved device-to-device and cycle-to-cycle uniformity with the standard deviation of Set/Reset voltages below 50 mV in experiment, which is among the lowest values ever reported for memristors. The concurrent achievement of all these performance metrics has not been accomplished with memristors built on either bulk oxides or polycrystalline 2D materials.
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Dhanya, I., i B. Sasi. "A Study on the Thermodynamics of Grain Growth in R.F. Magnetron Sputtered NiO Thin Films". Journal of Coatings 2013 (23.09.2013): 1–6. http://dx.doi.org/10.1155/2013/981515.
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Postdeposition annealing of thin nickel films synthesized using R.F. magnetron sputtering technique is carried in this study. The XRD analysis indicates that annealing of the nickel films leads to the formation of nickel oxide with a preferential growth along (200) plane. The oxidation mechanism is observed with a phase transformation and results in polycrystalline NiO films. The surface morphology of the thin films was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) as a function of annealing temperature. The studies indicate the formation of well-defined grain boundaries due to agglomeration of nanocrystallites. The films annealed in the range 573–773 K are found to be porous. The optical transmission spectra of the films annealed at 773 K exhibit interference effects for photon energies below the fundamental absorption edge. The optical studies indicate the existence of direct interband transition across a bandgap of 3.7 eV in confirmation with earlier band structure calculations.
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Carvalho, Sabrina, Eliana Muccillo i Reginaldo Muccillo. "Electrical Behavior and Microstructural Features of Electric Field-Assisted and Conventionally Sintered 3 mol% Yttria-Stabilized Zirconia". Ceramics 1, nr 1 (21.02.2018): 3–12. http://dx.doi.org/10.3390/ceramics1010002.
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ZrO2: 3 mol% Y2O3 (3YSZ) polycrystalline pellets were sintered at 1400 °C and by applying an alternating current (AC) electric field at 1000 °C. An alumina sample holder with platinum wires for connecting the sample to a power supply was designed for the electric field-assisted sintering experiments. The apparent density was evaluated with the Archimedes technique, the grain size distribution by analysis of scanning electron microscopy images, and the electrical behavior by the impedance spectroscopy technique. Sintering with the application of AC electric fields to 3YSZ enhances its ionic conductivity. An explanation is proposed, based on the dissolution back to the bulk of chemical species, which are depleted at the grain boundaries, leading to an increase in the oxygen vacancy concentration. For the enhancement of the grain boundary conductivity, an explanation is given based on the diminution of the concentration of depleted chemical species, which migrate to the bulk. This migration leads to a decrease of the potential barrier of the space charge region, known to be responsible for blocking the oxide ions through the intergranular region. Moreover, the heterogeneity of the distribution of the grain sizes is ascribed to the skin effect, the tendency of the AC current density to be largest near the surface, decreasing towards the bulk.
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Lagoeiro, Leonardo, Paola Ferreira i Cristiane Castro. "Crystallographic Control on the Development of Texture in Precipitated Quartz Grains". Materials Science Forum 495-497 (wrzesień 2005): 57–62. http://dx.doi.org/10.4028/www.scientific.net/msf.495-497.57.
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In this study we analysed microstructures and determined [c]-axis textures of quartz crystals in veins formed parallel to composition banding in naturally deformed iron oxide-quartz rocks. Only veins of few millimeters thick were sampled. These veins were formed in a regime of non-coaxial deformation under temperature of ~300°C. We made thin sections from rock slabs cut perpendicular to shear plane and parallel to shear direction. In thin sections veins are composed of large single quartz crystals of lens or rhomb-shaped blocks similar to s-porphyroclast systems. Lattice distortion (i.e. undulose extinction, gradual lattice banding and subgrain boundaries) occurs in single crystals as revealed by optical microscopy. Distortion was caused by slip of dislocations preferentially on basal planes. These are also planes along which microcracks developed. Distinct types of microcracks are individualized based on size, orientation and distribution of voids. Microcracrack voids are filled by polycrystalline quartz aggregates. In contrast to single crystals, these aggregates do not have any optical microstructure that might be related to crystal plastic process. Moreover grain size distribution are quite different from those related to dynamic recrystallized aggregates. Despite of that, polycrystalline quartz aggregates have strong [c]-axis preferred orientations. These orientations are similar to those of single crystals close to the microfracture walls. In large spaced voids c-axes orientation of quartz in polycrystalline aggregate have significant misorientation angles with respect to the single crystal [c]-axis orientation, reaching values up to 45° to the foliation plane (XY section of the finite strain). Based on microstructural and textural data we propose a mode for quartz [c]-axis texture development in both single crystals and polycrystalline aggregates that fill microcrack voids.