ELECTRICAL CHARACTERIZATION OF THE (LA,CA)(CR,CO)O-3 SYSTEM

The results of electrical conductivity and thermopower measurements are presented for selected (La,Ca)(Cr,Co)O-3 compositions. The La1-xCaxCrO3 compounds are typical p-type small polaron conductors. The La1-xCaxCoO3 compounds are found to be small polaron conductors at room temperature for x less than or equal to 0.20 with a higher electrical conductivity than the corresponding chromites. The electrical conductivity at room temperature is lower for Go-rich compositions than for Cr-rich compositions for compositions containing 10 mol% and 20 mol% Ca. This fact is attributed to the trapping of p-type small polarons at energetically lower Cr sites, resulting in a broad room temperature conductivity minimum. Above room temperature, the electrical conductivity increases with increasing Co content for all compositions. The thermopower for these compounds is interpreted using the Verwey electronic compensation mechanism including thermally activated disproportionation among Co ions.