High-temperature stability, structure and thermoelectric properties of CaMn 1 - x Nb x O 3 phases

• Published in: Acta materialia Vol. 57; no. 19; pp. 5667 - 5680
• Main Authors: Bocher, Laura, Aguirre, Myriam H., Robert, Rosa, Logvinovich, Dmitry, Bakardjieva, Snejana, Hejtmanek, Jiri, Weidenkaff, Anke
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2009
• Subjects: Perovskites; Structural transition; Thermal reduction; Thermoelectricity; Twinned domain microstructure; Twinned domain microstructure; Perovskites; Thermal reduction; Thermoelectricity; Structural transition
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2009.07.062

Polycrystalline perovskite-type CaMn 1 - x Nb x O 3 phases (with x = 0.02 , 0.05 , 0.08 and 0.10) were investigated with regard to their structure, microstructure and thermal stability as a function of temperature. The studied phases revealed a complex microstructure at room temperature with 90 ° twinned domains. At high temperatures, the manganate phases underwent a structural transition from orthorhombic to cubic symmetry, as confirmed by in situ high-temperature X-ray powder diffraction and electron diffraction data. Thermogravimetric heating/cooling studies showed a reversible thermal reduction/reoxidation process that occurred above a defined transition temperature. A possible mechanism relating the high-temperature structural transition and the thermal reduction process of slightly substituted CaMnO 3 phases was proposed. The thermal reduction process resulted in a change in the Mn 3 + / Mn 4 + concentrations in the Mn sublattice, and therefore in a modification of the transport properties. A comprehensive study examined the impact of both phenomena on the electrical and thermal transport properties.