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

The results of electrical conductivity and thermopower measurements ar e presented for selected (La,Ca)(Cr,Co)O-3 compositions. The La1-xCaxC rO3 compounds are typical p-type small polaron conductors. The La1-xCa xCoO3 compounds are found to be small polaron conductors at room tempe rature for x less than or equal to 0.20 with a higher electrical condu ctivity 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 energe tically lower Cr sites, resulting in a broad room temperature conducti vity minimum. Above room temperature, the electrical conductivity incr eases with increasing Co content for all compositions. The thermopower for these compounds is interpreted using the Verwey electronic compen sation mechanism including thermally activated disproportionation amon g Co ions.