Polaronic conduction in La2-xSrxCoO4 (0.25≤x≤1.10) below room temperature

Electrical transports in the La2-xSrxCoO4 system (0.25 less than or equal to x less than or equal to 1.10) below room temperature were investigated by bulk conductivities and dielectric properties in polycrystalline specimens, The bulk conductivities were obtained by complex-plane impedance analyses. For x less than or equal to 1.00, every specimen contains a dielectric relaxation process which yields the electron transfer integral, J. The J values in these specimens meet the requirements for hopping conduction of nonadiabatic small polarons, The relation between the energy required for the conduction and the energy responsible for the dielectric relaxation also ensures the nonadiabatic polaronic conduction. The peculiarity due to the ordered state shows up in the conduction at x = 0.50. For x greater than or equal to 1.00, every specimen involves a transition from the high temperature conduction process to the low temperature one. The transition point is near the Curie temperature, which indicates the strong correlation between spin alignment and carriers and also the change of the nature of carriers at the Curie point. (C) 1998 Academic Press.