Diffusion in systems with multi-well potential at Jahn-Teller or pseudo-Jahn-Teller ions

A theoretical investigation of peculiarities in the formation of diffusion potential barriers in non-metallic systems containing Jahn-Teller (JT) or pseudo-JT ions was made. It is shown that the form of potential barriers is essentially influenced by effects of degenerate term splitting by low-symmetry crystal fields. It is also influenced by double exchange connected with charge transfer between the cations closest to the diffusing atom and by JT interaction. The developed approach is used for analysis of the concentration dependence of oxygen-tracers diffusion coefficients in the high-temperature superconductor La2-xSrxCuO4-c. It is shown that the correlation typical for cooperative JT system between the concentrational dependences of the diffusion activation energy E-a(x) and temperature of structural phase transition T-D(x) exists.