Thermoelectric properties of CaMnO3 ceramics produced by using powder synthesized by modified Pechini method

Abstract

Calcium manganate (CMO) is a promising n-type semiconductor for thermoelectric applications due to its intrinsic properties. Still, these properties are highly dependent on the processing route used to produce these materials. In this work, properties of the polycrystalline CMO ceramics are reported by studying samples obtained from powders synthesized by a modified Pechini method and sintered at 1543K for 1, 3, 6, 12 and 24 h. Crystallographic parameters of the resulting phases were determined from X-ray diffraction patterns. The ceramics sintered for 6 h has the highest density (94.8%TD), while the CMO-1h sample (sintered only 1 h) presented the lowest density (77.2%TD) due to a large amount of secondary phase and short sintering time. The crystallite sizes of the CMO particles reached 49.2 nm; meanwhile, the grain sizes were in the range from 1.04 to 4.85 μm. Seebeck coefficient has a negative value, characterizing an n-type material, and its value approached −350 μV/K at 873K. The sample sintered for 1 h has the lowest value of thermal conductivity (3.3W/mK), while the ceramics sintered for 3 h reached maximum electrical conductivity value (1830 S/m), both at 873K. In addition, this high conductivity of the ceramics sintered for 3 h contributed to it having the highest ZT value of about 0.039.

Keywords

• thermoelectric oxide
• calcium manganite
• modified pechini method
• sintering time