Comparative Study in Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> and CaMnO<inf>3</inf> Perovskite Structure-Based Thermoelectric Oxide

Abstract

The p-type Ca3Co4O9 (CCO) and n-type CaMnO3 (CMO) thermoelectric oxide were synthesized stoichiometrically by the solid-state reaction technique. Both systems were investigated comparatively in aspects of thermoelectric and electrical properties. The material appearance, crystal structure, density, hardness, thermoelectric properties including Seebeck coefficient, electrical resistivity, and thermal conductivity, and electrical properties including dielectric constant, dielectric loss, and complex impedance of both systems were observed. Moreover, the P-E hysteresis loop of ferroelectric property and electrostriction were also investigated. The difference in the crystal structure, phase formation, and crystal growth conducts to the difference in physical, thermoelectric, and electrical properties. CMO was a cubic-perovskite type structure oxide with a higher density, less porosity, and smaller grain size with more thorough distribution as compared to orthorhombic structure CCO. Thus CMO could perform better values in terms of Seebeck coefficient, electrical resistivity, and thermal conductivity. In contrast, CCO possessed a larger grain size with an orthorhombic structure which has more favorable directions for dipole displacement. Hence, CCO exhibited a higher dielectric constant with lower dielectric loss. The complex impedance of both systems was in accordance with the RLC series circuit principle. Unfortunately, the P-E and S-E hysteresis loops of both systems could not be verified due to their electrical conductivity.