Perovskite substrates boost the thermopower of cobaltate thin films at high temperatures

Abstract

Transition metal oxides are promising candidates for thermoelectric applications, because they are stable at high temperature and because strong electronic correlations can generate large Seebeck coefficients, but their thermoelectric power factors are limited by the low electrical conductivity. We report transport measurements on Ca 3 Co 4 O 9 films on various perovskite substrates and show that reversible incorporation of oxygen into SrTiO 3 and LaAlO 3 substrates activates a parallel conduction channel for p-type carriers, greatly enhancing the thermoelectric performance of the film-substrate system at temperatures above 450 °C. Thin-film structures that take advantage of both electronic correlations and the high oxygen mobility of transition metal oxides thus open up new perspectives for thermopower generation at high temperature.

Confinement- and strain-induced enhancement of thermoelectric properties in LaNiO3/LaAlO3(001) superlattices

“…Another promising materials class for thermoelectric applications is cobaltates such as the mentioned Pd/Pt-based delafossites 10 or, in particular, the misfit-layered oxide Ca 3 Co 4 O 9 (CCO). [43][44][45] Remarkably, the 1/1 SLs can compete with this material, regardless of the underlying substrate (Table I). For a STO and a DSO , both the in-and cross-plane Seebeck coefficients of the 1/1 SLs are close to (or even exceed) the in-plane DFT results for pristine CCO, which are already much higher than DFT results for CCO strained to a STO .…”

“…The room-temperature values for the Seebeck coefficient and the power factor are compared to other topical oxide systems like La-doped STO 9,19,23 or layered cobaltates. [43][44][45] By contrasting the ultrathin SLs to the metallic longer-period (LNO) 3 /(LAO) 3 (001) case we point out the relevance of the MIT in obtaining a high thermoelectric response.…”

Tuning the Thermoelectric Properties of Transition Metal Oxide Thin Films and Superlattices on the Quantum Scale

“…The resulting conductivity thus strongly depends on the temperature and the oxygen pressure. For nominally pure single crystals, large oxygen pressures , and temperatures , the carrier concentrations are typically small, , which implies a significant positive Seebeck coefficient [ 17,82 ] (Figure 4a). The electrical resistivity decreases in the range .…”

“…Another prominent class of transition metal oxides is layered cobaltates such as the record‐value material , featuring a PF of , [ 14 ] or the misfit‐layered (CCO), [ 15,16 ] where values of and have been measured around room temperature for CCO films on STO(001). [ 17 ] Moreover, out‐of‐plane Seebeck coefficients of were predicted in delafossites such as and . [ 18,19 ] This exemplifies the beneficial role of structural anisotropy (either natural as in the bulk or artificial as in heterostructures) with regard to the thermoelectric properties.…”

Control of dopant crystallinity in electrochemically treated cuprate thin films

“…For example, oxygen off-stoichiometry is frequently tuned to optimize electrical and ionic conductivities in perovskite materials used as oxygen-transporting membranes or as elements of solid oxide fuel cells 8 . Similarly reversible oxygen doping of Ca 3 Co 4 O 9 films grown on SrTiO 3 and LaAlO 3 has been shown to enhance significantly the thermoelectric performance of the heterojunction 10 . In another example, controlled oxygen migration in materials such as VO 2−x or Ta 2 O 5−x can produce local metal-insulator transitions which may serve as the basis for resistive random access memory devices 9,11 .…”