Tendencies of p-Type Thermoelectric Oxide Semiconductor

Abstract

This report describes our research conducted on the tendencies of p-type thermoelectric oxide materials. Oxides which have 3rd transition metals as conductive center elements and low-dimensional conductive paths are candidates for p-type thermoelectric materials. Ln2NiO4 and NiO, NiLiO2, CoO and NaCo2O4 were prepared, and the relation between their crystal structures and electrical properties was studied. For a Ln2NiO4 system, the length of the c-axis plays an important role for Seebeck coefficients. For Ni and Co oxide systems, layer-like compounds such as NiLiO2 and NaCo2O4, were more conductive than isotropic ones, such as NiO and CoO. INTRODUCTION Recently, thermoelectricity has been developed and used in small-sized electric generating systems. However, thermoelectric conversion is not efficient enough for wide, multi-purpose use. Moreover, the most efficient materials currently used are based chalcogens, such as Bi2Te3, SbTe or PbTe. Because these materials cannot be used at high temperatures (above 600°C), and are toxic to both humans and the environment, restrictions are placed on their public use. Therefore, new oxide thermoelectric materials, which are refractory and chemically stable, which have highly efficient conversion rates, and which are non-toxic in nature, are expected to replace chalcogens in thermoelectric conversion. High electrical conductivity, low thermal conductivity, and a high Seebeck coefficient are necessary for highly effective thermoelectric materials. The figure of merit for energy conversion, Z, is defined in the following equation: