Search results for " Bo"
showing 10 items of 13775 documents
First principles hybrid Hartree-Fock-DFT calculations of bulk and (001) surface F centers in oxide perovskites and alkaline-earth fluorides
2020
Valuable discussions with E. A. Kotomin are gratefully acknowledged. Research contribution of R. E. and A. I. P. has been performed within the framework of the EUROfusion Enabling Research project: ENR-MFE19.ISSP-UL-02 “Advanced experimental and theoretical analysis of defect evolution and structural disordering in optical and dielectric materials for fusion applications.” The views and opinions expressed herein do not necessarily reflect those of the European Commission.
Complex structural contribution of the morphotropic phase boundary in Na0.5Bi0.5TiO3 - CaTiO3 system
2019
Abstract The correlation between structure and dielectric properties of lead-free (1-x)Na0.5Bi0.5TiO3 - xCaTiO3 ((1-x)NBT - xCT) polycrystalline ceramics was investigated systematically by X-ray diffraction, combined with impedance spectroscopy for dielectric characterizations. The system shows high miscibility in the entire composition range. A morphotropic phase boundary (MPB), at 0.09 ≤ x
Temperature Coefficients of Crystal Defects in Multicrystalline Silicon Wafers
2020
This article investigates the influence of crystallographic defects on the temperature sensitivity of multicrystalline silicon wafers. The thermal characteristics of the implied open-circuit voltage is assessed since it determines most of the total temperature sensitivity of the material. Spatially resolved temperature-dependent analysis is performed on wafers from various brick positions; intragrain regions, grain boundaries, and dislocation clusters are examined. The crystal regions are studied before and after subjecting the wafers to phosphorus gettering, aiming to alter the metallic impurity concentration in various regions across the wafers. Most intragrain regions and grain boundarie…
How Gettering Affects the Temperature Sensitivity of the Implied Open Circuit Voltage of Multicrystalline Silicon Wafers
2019
The temperature sensitivity of the open circuit voltage of a solar cell is mainly driven by changes in the intrinsic carrier concentration, but also by the temperature dependence of the limiting recombination mechanisms in the cell. This paper investigates the influence of recombination through metallic impurities on the temperature sensitivity of multicrystalline silicon wafers. Spatially resolved temperature dependent analysis is performed to evaluate the temperature sensitivity of wafers from different brick positions before and after being subjected to phosphorus diffusion gettering. Local spatial analysis is performed on intra-grain areas, dislocation clusters and grain boundaries. Lar…
Ab initio calculations of the electronic structure for Mn2+-doped YAlO3 crystals
2020
The electronic structure of Mn2+ ion substituted for the host Y atom in orthorhombic bulk YAlO3 crystals has been calculated by means of hybrid exchange-correlation functional HSE within density functional theory. The supercell approach has been used to simulate in Pbnm YAlO3 crystal the point defects, Mn-dopant and compensated the F+ center (oxygen vacancy with one trapped electron), to make unit cell neutral. Large 2 × 2 × 2 supercells of 160 atoms allow us to simulate substitutional point defect with concentration of about 3%. Mn2+ ions substituting for host Y form covalent Mn–O bonds, in opposite to the mostly ionic Y–O bond. The F center inserted to compensate the Mn2+ dopant in YAlO3 …
Variable-charge method applied to study coupled grain boundary migration in the presence of oxygen
2009
International audience; One of the important differences between simulation and experiments in grain boundary (GB)-dominated metallic structures is the lack of impurities such as oxygen in computational samples. A modified variable-charge method [Elsener A, Politano O, Derlet PM, Van Swygenhoven H. Modell Simul Mater Sci Eng 2008;16:025006] based on the Streitz and Mintmire approach [Streitz FH, Mintmire JW. Phys Rev B 1994;50:11996] is used to study coupled GB motion in an Al bicrystal with a [1 1 2] symmetrical tilt GB in the presence of substitutional O, and compared with the stick–slip process identified by Cahn and Mishin [Cahn JW, Mishin Y, Suzuki A. Acta Mater 2006;54:4953]. It is found…
Stabilization of primary mobile radiation defects in MgF2 crystals
2016
Abstract Non-radiative decay of the electronic excitations (excitons) into point defects ( F – H pairs of Frenkel defects) is main radiation damage mechanism in many ionic (halide) solids. Typical time scale of the relaxation of the electronic excitation into a primary, short-lived defect pair is about 1–50 ps with the quantum yield up to 0.2–0.8. However, only a small fraction of these primary defects are spatially separated and survive after transformation into stable, long-lived defects. The survival probability (or stable defect accumulation efficiency) can differ by orders of magnitude, dependent on the material type; e.g. ∼10% in alkali halides with f.c.c. or b.c.c. structure, 0.1% in…
Ion track template technology for fabrication of CdTe and CdO nanocrystals
2020
Abstract CdTe and CdO nanocrystals were synthesized by chemical deposition into a-SiO2/n-Si ion track template formed by 200 MeV Xe ion irradiation with the fluence of 108 ions/cm2. Depending on the temperature of the solution CdTe + CdO and single-phase CdO with a hexagonal crystal structure were obtained, respectively. The study of the current – voltage characteristics of the obtained structure with the single-phase CdO allows us to estimate the number of grain boundaries and the height of the potential barrier, as well as the n-type conductivity.
A comparative study on the compatibility of liquid lead–gold eutectic and liquid lead–bismuth eutectic with T91 and SS 316LN steels
2012
Abstract Liquid lead–gold eutectic (LGE) is considered as a potential target material for high power spallation sources. In the present work, the corrosion effects of LGE on T91 and SS 316LN steels have been investigated in comparison with that of liquid lead–bismuth eutectic (LBE) under the same testing conditions. Two tests were conducted at 400 °C for 1800 h and at 450 °C for 1300 h, in which specimens of the two steels were exposed to 1 m/s flowing LGE and LBE. Surface inspections showed that the specimens underwent a mixed corrosion mode of dissolution and oxidation. The results obtained from the SS 316LN specimens are very interesting. Firstly, EDX (electron energy dispersion X-ray sp…
The Grain Boundary Wetting Phenomena in the Ti-Containing High-Entropy Alloys: A Review
2021
In this review, the phenomenon of grain boundary (GB) wetting by melt is analyzed for multicomponent alloys without principal components (also called high-entropy alloys or HEAs) containing titanium. GB wetting can be complete or partial. In the former case, the liquid phase forms the continuous layers between solid grains and completely separates them. In the latter case of partial GB wetting, the melt forms the chain of droplets in GBs, with certain non-zero contact angles. The GB wetting phenomenon can be observed in HEAs produced by all solidification-based technologies. GB leads to the appearance of novel GB tie lines Twmin and Twmax in the multicomponent HEA phase diagrams. The so-cal…