Comparative Study in Ca₃Co₄O₉ and CaMnO₃ 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.

KEYWORDS:

• Perovskite structure
• thermoelectric oxide
• calcium cobalt oxide
• calcium manganite
• polycrystalline

Acknowledgments

The National Research Council of Thailand (NRCT), and Faculty of Science and Technology of Rajamangala University of Technology Suvarnabhumi, Thailand are gratefully acknowledged for all supports during this study. Prof. Dr. Rattikorn Yimnirun is sincerely acknowledged for all guidance.

Funding

This study is financially supported by the Research Fund for DPST Graduate with First Placement on Fiscal Year of 2559 from the Development and Promotion of Science and Technology Talents Project (DPST) and the Institute for Promotion of Teaching Science and Technology (IPST).