Low thermal conductivity of SrTiO₃−LaTiO₃ and SrTiO₃−SrNbO₃ thermoelectric oxide solid solutions

Abstract

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.

Modulation of electrical and thermal transports through lattice distortion in BaTi1–x Nb x O3 solid solutions

“…Similar behavior was also reported by other researchers both in La/Nb doped and oxygen-deficient BaTiO 3 , where a small polaron hopping of conduction mechanism was deduced [31][32][33][34]. In contrast, the μ Hall of STNO system is limited by large polarons [14]. The lattice distortion in BTNO will bring a much stronger trapping potential for carriers, resulting in the formation of small polarons.…”

“…However, comparing κ ele and κ, it could be found that κ is much lower than κ ele in BTNO at x0.6, even though the lattice structure is isotropic along the in-plane and cross-plane directions. A similar phenomenon was also found in STNO system [14]. This may be due to the different measurement directions of σ and κ, which results in a different scattering rate for electrons and phonons.…”

“…However, in order to realize dual modulations of electrical and thermal transport, materials with large modulation rate in electrical conductivity (σ) which can contribute κ by Wiedemann-Franz law is required [12]. We have reported previously that in SrTi1−xNbxO3 (STNO) solid solution system, σ can be increased from 720 S cm −1 to 49000 S cm −1 with a modulation ratio of ~68, and κ can be controlled from ~6 W m −1 K −1 to ~12 W m −1 K −1 with a modulation ratio of ~2, which present a promising strategy to develop electrical and thermal management materials by the homogenous system [13,14]. In STNO solid solution, due to the combined effects from polarons and conduction band transition, electron transport properties experienced a noticeable jump.…”

Study on Interfacial Effects on Thermal, Mechanical and Fluorescent Properties for SrTiO3-SrCeO3 Composites

“…Orthorhombic SrCeO 3 with good damage tolerance, proton conductivity, high coefficient of thermal expansion, and phase stability at 1200°C, has been a potential material for thermal barrier coatings and solid oxide fuel cells [8,9] . Due to a lattice distortion that could enhance the phonon and electron scattering, a solid solution, SrTiO 3 -LaTiO 3 , has a low thermal conductivity [10] . In SrTiO 3, with periodically twinning boundaries, the thermal conductivity can be decreased, as a result of the decrease in phonon mean free path [11] .…”

Seeking New Layered Oxyselenides with Promising Thermoelectric Performance

“…Oxides such as ZnO, In 2 O 3 , CaMnO 3 , and SrTiO 3 are chemically and thermally stable in air and the preparation process is easy and eco‐friendly, which have been indicated as promising candidates for high‐temperature TE applications. [ 25–34 ] However, the thermoelectric performance of those oxide semiconductors is much lower than that of alloys, owing to low carrier mobility and high thermal conductivity resulting from high electronegativity and remarkable ionic contribution to chemical bonding of oxygen atoms. Differently, layered oxygen‐containing compounds such as Na x CoO 2 and Ca 3 Co 4 O 9 have high carrier mobility and anisotropic thermoelectric properties, and layered oxyselenides such as Bi 2 O 2 Se and BiCuSeO also have strong anharmonicity and extremely low thermal conductivity.…”