Paper published as part of the special topic on Advanced Thermoelectrics Note: This paper is part of the special topic on Advanced Thermoelectrics. ARTICLES YOU MAY BE INTERESTED IN Influence of pressure assisted sintering and reaction sintering on microstructure and thermoelectric properties of bi-doped and undoped calcium cobaltite

Electron-doped SrTiO 3 has been attracting attention as oxide thermoelectric materials, which can convert wasted heat into electricity. The power factor of the electrondoped SrTiO 3 , including SrTiO 3 -LaTiO 3 and SrTiO 3 -SrNbO 3 solid solutions, has been clarified. However, their thermal conductivity (κ) has not been clearly identified thus far. Only a high κ (>12 W m −1 K −1 ) has been assumed from the electron contribution based on Wiedemann-Franz law. Here, we show that the κ of the electrondoped SrTiO 3 is lower than the assumed κ, and its highest ZT exceeded 0.1 at room temperature. The κ slightly decreased with the carrier concentration (n) when n is below 4 × 10 21 cm −3 . In the case of SrTiO 3 -SrNbO 3 solid solutions, an upturn in κ was observed when n exceeds 4 × 10 21 cm −3 due to the contribution of conduction electron to the κ. On the other hand, κ decreased in the case of SrTiO 3 -LaTiO 3 solid solutions probably due to the lattice distortion, which scatters both electrons and phonons. The highest ZT was 0.11 around n = 1 × 10 21 cm −3 . These findings would be useful for the future design of electron-doped SrTiO 3 -based thermoelectric materials.

Ferroelectricity and electrical conductivity are two fundamentally incompatible properties that are difficult to simultaneously achieve in a material. Here, we combine these two contradictory properties by embedding conducting SrNbO3 micro/nanopillars into a ferroelectric SrNbO3.5 (i.e., Sr2Nb2O7) thin film. The high-T c ferroelectric SrNbO3.5 thin film is epitaxially grown on a LaAlO3 substrate by pulsed laser deposition. The conducting SrNbO3 micro/nanopillars are introduced into the film via an electron-irradiation-induced SrNbO3.5-to-SrNbO3 phase transformation triggered by a focused electron beam. The sizes and distribution of the SrNbO3 micro/nanopillars can be accurately controlled through artificial manipulation of the electron-irradiation-induced SrNbO3.5-to-SrNbO3 phase transformation. The ferroelectric SrNbO3/SrNbO3.5 thin film with an in-plane polarization exhibits an electrical conductivity in the out-of-plane direction. Such conducting ferroelectric thin films may lead to the discovery of plentiful physical phenomena and have great potential for pyroelectric, photoelectric, and multiferroic applications.

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