Synthesis and thermoelectric properties of doubly substituted La 0.95 Sr 0.05 Co 1-x Cr x O3 (0 ≤ x ≤ 0.5)
Résumé
Dense La$_{0.95}$Sr$_{0.05}$Co$_{1-x}$Cr$_x$O$_3$ (0 ≤ x ≤ 0.5) ceramics were synthesized by solid-state reaction and conventional sintering. Room-temperature crystal structure and microstructure were investigated and the thermoelectric properties were measured in the temperature range 323 K–1020 K. La$_{0.95}$Sr$_{0.05}$Co$_{1-x}$Cr$_x$O$_3$ is a p-type small polaron conductor. The charge carrier concentration is determined by both substitution of La3+ with Sr2+ and thermally-activated charge disproportionation of Co$^{3+}$ and /or Cr$^{3+}$. The variation of electrical conductivity versus Cr content is ascribed to the trapping of p-type polarons at Cr sites. By substituting Co with Cr, the power factor below 800 K is reduced and that above 800 K is improved. The thermal conductivity is effectively reduced by doping Cr. Substitution of Co with Cr greatly enhances the high-temperature (700 K–1000 K) ZT values, reaching 0.04 at 1000 K for La$_{0.95}$Sr$_{0.05}$Co$_{0.5}$Cr$_{0.5}$O$_3$.