High-Temperature Thermoelectric Properties of Sol-Gel Processed Ca_(2.5)Ag_(0.3)RE_(0.2)Co_4O_9 (RE: Y and Rare-Earths) Materials

摘要

Herein, dually doped Ca_(2.5)Ag_(0.3)RE_(0.2)Co_4O_9 [RE: La, Pr, Nd, Sm, Gd, Dy, Er, Yb, Eu, Tb, Ho, Lu, Ce, and Y) samples are synthesized by sol-gel technique and consolidated by cold pressing under high pressure to systematically scrutinize the influences of Y and rare-earth dually doping with Ag on transport properties of Ca_3Co_4O_9 for high-temperature thermoelectric (TE) applications. Characterization results reveal that targeted phase is successfully produced, and doping of the compositions is provided. Doping of Y and rare-earth elements together with Ag into the Ca~(2+) site is effective in increasing the Seebeck coefficient and decreasing the electrical resistivity of the samples, thanks to the reduction in carrier concentration. Thermal conductivity of the samples is reduced related to the lower relative densities and alloy scattering originated from dually doping. Among the samples, Ca_(2.5)Ag_(0.3)Ho_(0.2)Co_4O_9 and Ca_(2.5)Ag_(0.3)Eu_(0.2)Co_4O_9 exhibit the highest power factor (PF) values of 0.65 and 0.62 mW m~(-1) K~(-2) at 800 °C, respectively. These results are quite high for bulk oxide TE materials which can be assessed as potential oxide TE materials for high-temperature TE power generation.