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Description
Computational methods are an important component of studies for understanding materials properties, from their crystallographic structure, to their physical properties. Kaganer method [1], a theoretical model developed to determine the densities of threading dislocation in thin films, and ab initio calculations, performed to obtain information about structural stability and physical properties of some metallic hydrides [2], will be presented.
In epitaxial thin films, structural defects are inevitably present. To investigate these defects, Kaganer method was employed to determine the densities of threading dislocations. These parameters were extracted from X-ray diffraction profiles measured in skew geometry, using a computational model proposed by Kaganer et al. [1] that investigates the broadening and the profile of X-ray diffraction peaks. Asymmetric (hkl) reflections were used to extract the edge dislocation density, ρₑ, and the corresponding correlation length, Lₑ, while symmetric (000l) reflections were measured to determine the screw dislocation density, ρₛ, and correlation length, Lₛ. The method was applied to several materials, grown as thin films: GaN, Cr, and SrLaCuO.
Using different DFT codes, such as CALYPSO, SIESTA, and ELK, alternative approaches for identifying promising hydride superconductor candidates, that typically are stable only under applied pressures of several tens to hundreds of GPa [3], were explored through ab initio calculations. A series of input parameters, with different roles for each code, were tested in order to calculate electron–phonon interactions and to estimate the critical temperature (Tc) of various hydride compounds (e.g., CrxHy, PdH, and Pd1−xCuxHy). Furthermore, these materials were grown by RF sputtering as thin films with thicknesses on the order of tens of nanometers, after which their crystal structure and physical properties were investigated.
References:
[1] Kaganer, V.M., Brandt, O., Trampert, A., Ploog, K.H., X-ray diffraction peak profiles from threading dislocations in GaN epitaxial films. Phys. Rev. B Condens. Matter Mater. Phys. 2005, 72, 045423.
[2] Shipley, Alice M., et al. "High-throughput discovery of high-temperature conventional superconductors." Physical Review B 104.5 (2021): 054501.
[3] Duan, Defang, et al. "Structure and superconductivity of hydrides at high pressures." National Science Review 4.1 (2017): 121-135.
