Effects of pressure on the structural, electronic, and elastic properties of superconductor material with perovskite structure YBa2Cu3O7: insights from ab initio calculation

Superconducting materials' crystal lattices and electronic structures have fascinated the materials science research group. In the present work, we have investigated and discussed the structural, electronic, and elastic properties of single-crystal YBa₂Cu₃O₇ under pressure up to 20 GPa using the first principal calculations based on the density functional theory (DFT). The results showed that this compound's calculated lattice parameters under zero pressure agree with the experimental results. The calculated band structures and the DOS show that YBa₂Cu₃O₇ is metallic. The width of the electronic band increases with pressure, due to the increased overlap of the orbitals. The pressure-dependent single-crystal elastic constants ensure mechanical stability. The calculated value of Poisson’s ratio (n ~ 0.32) suggests that the compound is ductile and that the metallic contribution dominates our material. The variations of anisotropy indices show a monotonic dependence on pressure, indicating that the studied material becomes elastically anisotropic while increasing the pressure. Debye temperature and sound velocity were calculated from the elastic constants and crystal density. They increase systematically with pressure. Our material also appears to have high Debye temperatures, indicating that it may have high thermal conductivity. Finally, we have calculated and discussed the optical properties at ambient pressure (dielectric function, absorption, refractive index, conductivity, loss function, and reflectivity) for both polarization directions [100] and [001].

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