Texture development in Bi1.5Pb0.5Sr1.7Y0.5Co2O9−δ layered cobaltite by high-temperature compression deformation and its effect on thermoelectric properties

Texture development in Bi1.5Pb0.5Sr1.7Y0.5Co2O9−δ (BPSYO) layered cobaltite by plastic deformation is examined experimentally by high-temperature uniaxial compression, in order to develop a method to reduce the resistivity of thermoelectric cobaltite by controlling the spatial arrangement of the (0 0 1) conductive CoO2 layers. It is found that the present oxide can be plastically deformed up to a true strain of −2.2 at 1113 K with strain rates in the order of 10−5 s−1. It is concluded that high-temperature compression is effective both for densification and texture development. Evolution of (0 0 1) (compression plane) texture is experimentally confirmed as expected from the crystal structure, where a dislocation that has a small Burgers vector may move in the (0 0 1) plane. The formation of a sharp (0 0 1) texture results in a reduction in resistivity to about one-tenth of that of the specimen without texture. The estimated value of the dimensionless thermoelectric figure of merit is 0.11 at 973 K, which is close to the practical level of a thermoelectric material.