Effect of A-site cation ordering on the thermoelectric properties of the complex cobalt oxides Gd1-xSrxCoO3-delta (x=0.8 and 0.9)

The effect of substitution of Sr²⁺ ions for Gd³⁺ ions on the phase composition, electrical resistivity, thermoelectricity, and thermal conductivity of rare-earth cobalt oxides Gd_1-xSr_xCoO_3-δ (x = 0.8 and 0.9) has been investigated. It has been determined that at the investigated strontium concentrations, the single-phase disordered nonstoichiometric cubic perovskites and superstructures with ordered Sr²⁺/Gd³⁺ ions and anion vacancies can be formed. The influence of ordering/disordering of Gd and Sr cations over crystal-lattice A- sites on the thermoelectric figure of merit and sample stability at high temperatures has been studied. The thermoelectric figure of merit of the disordered samples was found to exceed by far the analogous parameter of the ordered samples, which allows us to consider the disordering as a way of improving the thermoelectric parameters. Two contributions to the conductivities are discussed: high-temperature thermoactivation and low-temperatures variable range hopping. The parameters of the Mott electronic structure, including DOS N(ε_F), hopping energy ε (the energy of hopping conductivity activation), and hopping length R_h, have been estimated