Molecular Dynamics Simulation of High-T_c Superconductors

Abstract

We present the results of MD simulations of oxygen diffusion in YBa₂Cu₃O_{7 – x} (x = 0.09 – 0.27) at 1350–1500 K employing Born model potentials. No strong stoichiometry dependence of the oxygen diffusion is observed. The variation in the oxygen diffusion coefficients is found to be less than 70% in the x range 0.09–0.27 which is in agreement with experimental data. Changes in stoichiometry are found to cause the redistribution of oxygen, which may be the reason for the lack of a strong stoichiometry dependence of the diffusion coefficient in YBa₂Cu₃O_{7 – x}. Moreover, we find that the oxygen migration mechanisms in YBa₂Cu₃O_{7 – x} are the same in the x range 0.09–0.27: the oxygen vacancies migrate between O(1), O(4) and O(5) sites. The possible oxygen-ion jump paths are observed to be O(1)–O(5), O(1)–O(4), and O(4)–O(5), but not O(5)–O(5).

Key Words:

• High T_c -superconductors
• oxygen diffusion