Thermoelectric properties of oxygen-deficient spinel-type ZnxFe3−xO4−δ prepared by carbothermal reduction and spark plasma sintering

Abstract

This paper describes the effect of oxygen vacancies, which are induced by a carbothermal reduction process and spark plasma sintering (SPS) treatment, on the thermoelectric properties of spinel-structured zinc ferrites ZnxFe3−xO4 (0.2 ≤ x ≤ 1.0). Characterization of the oxygen-deficient ZnxFe3−xO4−δ materials revealed that Zn2+ preferentially occupy the octahedral B-sites and that valence modification of Fe3+ to Fe2+ occurred, resulting in an excess of n-type carriers at B-sites and an increased power factor. In addition, Co substitution enhanced the power factor for the materials over the entire investigated temperature range. Compared with the carbothermal reduction process, SPS treatment effectively introduced oxygen vacancies within a short time and resulted in a material with a substantially improved electrical conductivity.