Perovskite thermoelectric materials for high-temperature energy conversion
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Despite of recent success in achieving the figure of merit ZT > 1 based on the nanoscale patterned thermoelectric structures, there have been few stable n-type materials with attractive thermoelectric responses for high temperature applications at T > 800K. In this thesis, we applied the first-principles density functional theory (DFT) calculations to probe the structure and thermoelectric properties relationship of a comprehensive series of perovskite materials. The density of states (DOS), Seebeck coefficient S, electric conductivity σ, and electronic contribution of the thermal conductivity Ke were obtained directly from the first-principles DFT calculations. In particular, Lanthanum (La), Gadolinium (Gd), Samarium (Sm), Yttrium (Y) doped MU+2093SrU+2081U+208BU+2093TiOU+2083 and Niobium (Nb) doped SrNbyTi1-yOU+2083 and doubly doped LaU+2093SrU+2081U+208BU+2093NbyTi1-yOU+2083 systems were studied. The change of the power factor S^2σ corresponding to the different dopant concentration had a good agreement with the experimental data. Our computed power factors S^2σ as a function of the dopant con- centration agree well with the available experimental data, and at the same time provide new insights for the optimal compositions. In the low doping region (x U+003E 12:5%), gadolinium and niobium are the best candidates of perovskite thermoelectric materials while at high doping level (x U+003E 25%), lanthanum and yttrium are the best options. In the case of doubly doped perovskites LaU+2093SrU+2081U+208BU+2093NbyTi1-yOU+2083, our calculations predict that the x= 12.5% and y= 12.5% is the best choice.
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