S. N. Savvin

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

The processes of oxygen diffusion in La2 − xSrxCuO4 − δ 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 − δ 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 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.

Oxygen Diffusion in La2-xSrxCuO4-δ: Molecular Dynamics Study

The oxygen mobility in La2-xSrxCuO4-δ (x=0.15; 0.6; 1) was studied by the Molecular Dynamics (MD) technique. The parent layered La2CuO4 crystal structure has been shown to give rise to a strong anisotropy of oxygen diffusion coefficient in the lattice. Equatorial oxygen sites in(CuO2) layers were found to provide the paths of the fast oxygen transport in the structure, while the axial ones in (La2O2) blocks were substantially less mobile. The influence of the dopant concentration on structural properties and energetic characteristics of the oxygen migration are discussed. Analysis of the ion trajectories obtained during the simulation allowed explaining the observed dependence of the oxygen diffusion activation energies on the strontium content and provided further insight into the mechanism of oxygen diffusion in the oxides.

Oxygen mobility in layered cuprates La2−xSrxCuO4−δ

Abstract Oxygen mobility in layered lanthanum cuprates La 2− x Sr x CuO 4− δ is studied by dynamic-thermal isotope exchange method and coulometric titration. Depending on the temperature, different preferred surface exchange reactions are realized. Such characteristics of bulk diffusion process as activation energy and diffusion coefficient are stated for the cuprates. Theoretical modeling of diffusion process in La 2 CuO 4 and LaSrCuO 3.5 phases is carried out using molecular dynamics simulations. The data obtained are compared to the ones previously obtained experimentally.

Cationic transport mechanism in α-Ag1 − xCuxI(0 < x < 0.25): Molecular-dynamics simulation

The structural and transport characteristics of an Ag1 − xCuxI(0 < x < 0.25) solid solution have been simulated by the molecular-dynamics method. It is found that the cation diffusion coefficient decreases with increasing copper concentration; this correlation is in agreement with the experimentally observed decrease in ionic conductivity. It is shown that the cationic transport in disordered Ag1 − xCuxI phases is mainly due to the migration of silver cations, whereas the mobility of copper cations is much lower. Cu+ cations are found to reside in the 8c positions in a bcc cell; this finding suggests the existence of nanoscale α-CuI regions.