Thermoelectric Properties and Microstructure of Modified Novel Complex Cobalt Oxides Sr₃RECo₄O_10.5 (RE = Y, Gd)

We report on the high-temperature thermoelectric properties and microstructure of modified novel complex cobalt oxides Sr3RECo4O10.5 (RE = Y, Gd), in which the Sr- and Co-sites are partly substituted by Ca and Ga, respectively. We have found that the sample with RE = Gd shows a significant higher electrical conductivity (sigma) than the RE = Y sample, while their Seebeck coefficients (S) remain almost the same over the whole measured temperature range. With Ga substituting for Co, S is enhanced and further increased by the dually doping with Ca at the Sr-site, leading to an improvement of the thermoelectric power factor (sigma S-2). At 1150 K, the highest sigma S-2 value attains for the Sr2CaGdCo3.9Ga0.1O10.5 sample about 60 mu Wm(-1)K(-2), which is 8 times larger than the Sr3GdCo4O10.5 counter-part. Interestingly, although microstructure shows a clear evolution of the grains for the Ga and Ca doped-sample resulting in a substantial decrease in porosity, its thermal diffusivity exhibits a lower value then the non-doped one, particularly in high temperature region. © 2012 American Institute of Physics