The thermoelectric properties of a nonstoichiometric titanium oxide (TiO_(1.1)) are investigated in terms of materials for high-temperature thermoelectric conversion. The electrical conductivity, σ, of TiO_(1.1) increases to 9000 S/m at 1073 K, is showing semiconducting behavior. The Seebeck coefficient, α, of TiO_(1.1) shows a general trend in which the value increases gradually from 0.4 mV/K at 573 K to 1.0 mV/K at 1223 K. As a consequence, the power factor, α~(2)σ, reaches 8.6×10~(?3) W/(m·K~(2)), the largest value of all reported oxide materials. The thermal conductivity, κ, of TiO_(1.1) increases with temperature, from 1.3 W/(m·K) at 573 K to 7.1 W/(m·K) at 1223 K. In spite of the considerably large values of κ, the figure of merit, Z = α~(2)σ/κ, reaches 1.6×10~(?3) K~(?1) for TiO_(1.1) at 973 K. The extremely large power factor of TiO_(1.1) compared to other metal oxides can be attributed to the optimal carrier density. The dimensionless figure of merit, ZT, of 1.64 attained by TiO_(1.1) at 1073 K is the largest value of all reported other thermoelectric materials in this temperature region. And that TiO_(1.1) has ZT values of nearly unity or greater in the range of 773 to 1223 K, demonstrates the usefulness of the nonstoichiometric titanium oxides for high-temperature thermoelectric conversion.
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