Improvement in thermoelectric properties of (ZnO)₅In₂O₃ through partial substitution of yttrium for indium

We first measured the thermoelectric properties of layer-structured homologous compounds, (ZnO)_mIn₂O₃ (m = integer), and reported that they would becomecandidate materials for high-temperature thermoelectric energy conversion.^1–4 We further tried to improve their thermoelectric properties by partially substituting yttrium for indium in (ZnO)₅In₂O₃. Though the ionic radius of Y³⁺ is larger than that of In³⁺, the a-axis (hexagonal system) elongated and c-axis shrank as Y was substituted for In. The thermoelectric properties were found to vary with a varying amount of Y substitution; 3% Y substitution gave rise to the largest thermoelectric figure of merit, i.e., 1.1 - 1.3 × 10^-4 K^-1 at 960–1100 K. The abnormal change in the lattice structure by Y substitution was responsible for the unusual behavior of the thermoelectric properties.