Role of Structure and Defect Chemistry in High-Performance Thermoelectric Bismuth Strontium Cobalt Oxides

Abstract

Bi0.87SrO2]2[CoO2]1.82 (BSCO) is one of the best p-type thermoelectric oxides but its structural and electronic properties are still little understood. BSCO is a misfit-layered compound consisting of an incommensurate stacking of hexagonal CoO2 and double rock-salt BiSrO2 layers. Here we combine experimental and computational approaches to investigate its crystallographic and electronic structure as well as thermoelectric transport properties. Considering different approximations for the subsystems stacking we present a structural model that agrees well with both bulk and atomic-scale experimental data. This model, which suggests a level of Bi deficiency in the rock-salt layers, is then W Bdeficiency leads to a band-gap opening and increases p-type electronic conductivity due to the formation of Co 4+ species that serve as itinerant holes within the predominantly Co 3+ framework of the CoO2 layer. We validate these predictions using electron energy loss spectroscopy in the scanning transmission electron microscope. The relationship between the hole-doping mechanism and the changes of the local structure (in particular the level of Bi deficiency) is evaluated. The reliability of the simulations is supported by the calculated temperature dependence of the Seebeck coefficient, in good agreement with experimental measurements.

Prospects for Engineering Thermoelectric Properties in La1/3NbO3 Ceramics Revealed via Atomic-Level Characterization and Modeling

“…38 The CRTA methodology has been successfully applied to other oxide thermoelectric materials. [39][40][41] Within this methodology, is exactly cancelled in the expression of the Seebeck coefficient, and thus can be directly evaluated from the first-principles band structure.…”

Anisotropic Heat Conduction in Ion‐Substituted Layered Cobalt Oxides

“…The measured thermal conductivity values in this study are low compared to the computational results. It is difficult to direct comment on this discrepancy at this stage, but it can be attributed to structural defects in the films or limitations in applying computational results (bulk single crystal) to thin films. LiCoO 2 exhibited the highest κ in all directions, while Ca 0.33 CoO 2 shows the strongest anisotropy (κ || /κ ⊥ ≈ 6.2).…”

Experimental corroboration of the thermoelectric performance of Bi2PdO4 oxide and Pb-doped derivatives

“…The finding of great thermo-power value (characterised by the Seebeck coefficient) in the layered Na x CoO 2 oxides 5,6 encouraged the scientific community to explore new transition metal oxides as potential thermoelectric materials, such as SrTiO 3 , 7 a well-known n-type oxide with large power factor and other layered cobaltite compounds as La 0.8 Sr 0.2 CoO 3 , Ca 3 Co 4 O 9 8 and Bi 2 Sr 2 Co 2 O y , which display promising thermoelectric properties. 9,10 As enumerated herein, there are many advantages in using transition-metal oxides compared to other thermoelectric materials; for instance, the electronic properties can be easily tailored, they exhibit a broad range of electric properties as well as thermal behaviours, and the physics of the phonons in these compounds have been deeply studied and comprehended. 11 However, transition-metal oxides also present some drawbacks such as poor electrical conductivity with low charge-carrier mobility and high thermal conductivity.…”