Optimization of Sintering Temperature for Maximizing Dimensionless Figure of Merit of La-Doped Strontium Titanate Thermoelectric Material in the Combination of Combustion Synthesis with Post Spark Plasma Sintering

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This paper describes thermoelectric properties of La-doped SrTiO₃ prepared by using a combination of combustion synthesis (CS) with post spark plasma sintering (SPS), on which effects of sintering temperature were mainly examined. In experimental, combustion-synthesized (CSed) samples (Sr_1−xLa_xTiO₃, x=0.08) were spark-plasma-sintered (SPSed) at temperatures from 1513 to 1663 K and the thermoelectric properties of sintered Sr_0.92La_0.08TiO₃ were measured from room temperature to 1073 K. In experimental sintering temperature range, sintering temperature didn’t heavily affect the average grain size of sintered SLTO in the case that sintering temperature ranges from 1543 to 1603 K. However, when sintering temperature rose over 1603 K, the average grain size of sintered SLTO was dramatically affected and it increased with sintering temperature. With increasing sintering temperature, the effects of phonon scattering at grain boundaries decreased therefore, thermal conductivity of all sintered samples increased with sintering temperature. With increasing sintering temperature, electric conductivity of sintered SLTO increased and absolute value of Seebeck coefficient of sintered SLTO decreased because sintering at higher temperature caused the more oxygen defects which generate the larger carrier density. In conclusion, the product sintered at 1573 K showed the maximum of the dimensionless figure of merit of 0.16 at 1005 K.