Simulation of ion transport in layered cuprates La2-xSrxCuO4-δ

The processes of oxygen diffusion in La2-xSrxCuO4-delta phases have been simulated for the first time by the molecular-dynamics method. Calculations were performed for the temperature range 300-2500 K. The behavior of the radial pair correlation functions, which characterize the degree of order of O1 ions in CuO2 layers, indicates that O2- anions form a weakly correlated subsystem within a CuO2 layer. To quantitatively confirm the conclusions about the predominantly two-dimensional character of ion transport and different mobilities of O1 and O2 particles in the cuprates under study, the pair oxygen diffusion coefficients in the La2-xSrxCuO4-delta lattice were calculated. It is shown that oxygen diffusion occurs through the conventional hopping mechanism mainly in CuO2 layers; correspondingly, the diffusion coefficient for equatorial ions (O1) exceeds that for apical oxygen anions (O2) by an order of magnitude. The motion of oxygen anions was traced L at the microscopic level through analysis of the particle transport trajectories. It has been proven for the first time that diffusion of O1 ions in the ab plane in a nonstoichiometric LaSrCuO3.61 sample occurs through jumps to the nearest position or along CuO2 layers; in a more complicated way, it may occur through unoccupied O2 lattice sites.