Spin-state transition in the layered barium cobaltite derivatives and their thermoelectric properties

Abstract

Ba1.9Me0.1Co9O14 (Me = Ba, Sr, Ca) (BCO) layered cobaltites were prepared by means of solid-state reactions method. Crystal structure, microstructure, thermal expansion, electrical conductivity, and thermo-EMF for the obtained oxides were studied; the values of their linear thermal expansion coefficient, activation energy of electrical transport, and power factor values were calculated. It was found that BCO are p-type semiconductors, in which the spin-state transition occurs within 460–700 K temperature interval due to change in spin state of cobalt ions, which accompanied the sharp increase in electrical conductivity, activation energy of electrical conductivity, and linear thermal expansion coefficient, while thermo-EMF coefficient decreased. Partial substitution of barium by strontium or calcium in BCO leads to the increase in spin-state transition temperature and electrical conductivity of the samples, and, at the same time, thermo-EMF coefficient; consequently, their power factor values decrease.