Effects of Sintering Temperature on Thermoelectric Device of La-Doped Strontium Titanate in the Combination of Combustion Synthesis and Spark Plasma Sintering

Abstract

Thermoelectric properties of La-doped SrTiO 3 were investigated in order to determine the optimum sintering temperature for its fabrication by using a combination of combustion synthesis and spark plasma sintering. Combustion-synthesized samples (Sr 1Àx La x TiO 3 , x ¼ 0:08) were subjected to spark plasma sintering at temperatures from 1513 to 1663 K. The average grain size of sintered Sr 0:92 La 0:08 TiO 3 enlarged as sintering temperature rose up. The maximum average grain size was 23.5 mm for a sintering temperature of 1663 K. The thermoelectric properties of sintered Sr 0:92 La 0:08 TiO 3 were measured from room temperature to 1073 K. The optimum sintering temperature in the experimental sintering temperature range was 1633 K. Among the samples, the Sr 0:92 La 0:08 TiO 3 sample sintered at 1633 K showed the maximum power factor of 1:51 Â 10 À3 Wm À1 K À1 at 375 K. Further, we investigated the effects of pressing direction during sintering on the thermoelectric properties of combustion-synthesized Sr 0:92 La 0:08 TiO 3 . The combustion-synthesized samples were sintered well along the pressing direction during sintering; therefore, the electric conductivity measured along the pressing direction during sintering was more than twice that measured along the direction perpendicular to the pressing direction during sintering. Thus, we concluded that pressing direction during sintering affected the electric property of Sr 0:92 La 0:08 TiO 3 .

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

“…There is no difference between the XRD patterns obtained before and after SPS, indicating that secondary-phase has not appeared during sintering. Also, we confirmed that the SEM image 22) didn't show secondary-phase in SPSed products. Figures 2(a), (b) and (c) show the temperature dependence of , and of CSed and SPSed SLTO for various sintering temperatures, respectively.…”

“…22) The average grain size of SLTO sintered at 1513, 1543, 1573, 1603, 1633, and 1663 K was approximately 1.32, 4.31, 3.61, 2.32, 6.63, and 23.5 mm, respectively. 22) The average grain size of sintered SLTO decreased above 1573 K, but it increased again above 1603 K. In experimental sintering temperature range, sintering temperature didn't heavily affect the average grain size of sintered SLTO in the case of 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. Table 1 lists the lattice parameters of synthesized powders before SPS calculated from XRD data and comparison of sintering temperatures and bulk density after SPS.…”

“…22) Then, pulverized powders were sintered by SPS (SPS-511S, Sumitomo Coal Mining, Tokyo, Japan) at a heating rate of 30 Kmin À1 and a holding time of 15 min in vacuum. During sintering, the mechanical pressure was maintained at 34 MPa by using plungers.…”

“…22) After combustion-synthesis, the obtained products were pulverized into powders in a planetary ball mill (Pulverisette 6, Fritsch, Idor-Oberstein, Germany) operated at 350 rpm for 40 min in air. The particle size of the obtained powders was within 5 mm.…”

Enhancement of thermoelectric performance in strontium titanate by praseodymium substitution

“…For x 0.10, the power factor exhibits similar behaviour with that observed for Sr 1 x La x TiO 3 and La 0.1 Sr 0.9 x Dy x TiO 3 ceramics. 17,22,40 The maximum power factor of $1400 lW m 1 K 1 at 670 K was observed for Sr 0.90 Pr 0.10 TiO 3 , in accordance with the trends …”