Ca-for-Sr substitution in the thermoelectric [(Sr,Ca) 2(O,OH) 2] q[CoO 2] misfit-layered cobalt-oxide system

Abstract

Calcium-for-strontium substituted samples of the misfit-layered cobalt-oxide system, [(Sr 1− x Ca x ) 2(O,OH) 2] q [CoO 2], were successfully synthesized up to x=0.2 with a sample-encapsulation technique originally developed for the x=0 end phase. While the x=0 sample has a commensurate match between the two layer blocks (i.e. q=0.5), isovalent Ca-for-Sr substitution induces lattice misfit (i.e. q>0.5). At the same time the Seebeck coefficient gets increased, but the increase in resistivity results in suppressing the thermoelectric power factor. The magnetic anomaly in the x=0 sample gets released upon the Ca substitution for the x=0.2 sample to exhibit an almost Curie–Weiss behavior. It is concluded that with increasing x in [(Sr 1− x Ca x ) 2(O,OH) 2] q [CoO 2] the properties smoothly evolve towards those previously reported for the x=1.0 end member, [Ca 1.7O 2.1H 2.4] 0.58[CoO 2].