Enhanced thermoelectric properties of Bi2Sr2Co2Oy by alkali metal element doping and SiC dispersion

Bi2Sr2Co2Oy (BSCO) is a layered cobalt-based oxide whose thermoelectric properties have been extensively studied recently because its layer structure of CoO2 gives good electrical conductivity. SiC, with larger Seebeck coefficients and higher electrical conductivity, is also widely concerned in the field of thermoelectricity. In this paper, the effects of alkali metal element doping and SiC dispersion on thermoelectric properties of BSCO are studied for two series samples of Bi1.85Na0.15Sr2Co2Oy + m wt% SiC (m = 0, 0.025, 0.05, 0.1, and 0.15) and Bi1.9K0.1Sr2Co2Oy + z wt% SiC (z = 0, 0.025, 0.05, 0.1, and 0.15). After Na+ and K+ replacing Bi(3+ )sites, the electrical resistivity of BSCO is reduced by the increased hole concentration. On the basis of the optimized Na+ and K+ doping, nano-SiC particles are dispersed on the BSCO matrix, which increases the phonon scattering at the interface and greatly reduces the thermal conductivity. Meanwhile, the Seebeck coefficients of Bi2Sr2Co2Oy materials are basically unchanged under the combined action of cation doping and SiC dispersion. The maximum ZT values of 0.26 and 0.24 at 923 K are obtained for m = 0.025 and z = 0.05 Bi2Sr2Co2Oy-based samples, respectively.