Abstract
A-site deficient perovskites are among the most important n-type thermoelectric oxides. Ceramics of Sr1−xPr2x/3□x/3TiO3 (x = 0.1–1.0) were prepared by solid-state reaction at 1700–1723 K using highly reducing atmospheres. Samples with the highest Sr content had a cubic crystal structure ; incorporating Pr with A-site vacancies led to a reduction in symmetry to tetragonal (I4/mcm) and then orthorhombic (Cmmm) crystal structures. HRTEM showed Pr2/3TiO3 had a layered structure with alternating fully and partially occupied A-sites and a short-range order along the (100) direction. Electrical conductivity was highest in samples of high symmetry (x ≤ 0.40), where the microstructures featured core-shell and domain structures. This enabled a very high power factor of approximately 1.75 × 10−3 W m−1 K−2 at 425 K. By contrast, at high Pr content, structural distortion led to reduced electron transport; enhanced phonon scattering (from mass contrast, local strain and cation–vacancy ordering) led to reduced, glass-like, thermal conductivity. Carbon burial sintering increased the oxygen deficiency leading to increased carrier concentration, a maximum power factor of approximately 1.80 × 10−3 W m−1 K−2 at 350 K and thermoelectric figure of merit of 0.26 at 865 K. The paper demonstrates the importance of controlling both crystal structure and microstructure to enhance thermoelectric performance.This article is part of a discussion meeting issue ‘Energy materials for a low carbon future’.
Highlights
Harvesting energy from waste heat using thermoelectricity is attracting increasing interest as a possible sustainable energy technology [1,2,3,4,5]
The low abundance and toxicity of the constituent elements of the traditional thermoelectric materials combined with their restricted operating range limit the large scale application of these materials [2]
Interest in oxide thermoelectrics was stimulated by the discovery of promising thermoelectric performance for layered NaCo2O4 [4]; this was followed by other p-type oxides with encouraging properties [5]
Summary
Harvesting energy from waste heat using thermoelectricity is attracting increasing interest as a possible sustainable energy technology [1,2,3,4,5]. In order to maximize the ZT, it is necessary to have materials with high electrical conductivity and Seebeck coefficient, and low thermal conductivity The interrelationship between these parameters through their dependency on carrier concentration makes the enhancement of ZT challenging [1]. Atomic-scale defects are necessary to enhance phonon scattering and thereby reduce thermal conductivity Such defects include substituting cations [8,9], oxygen vacancies [10,11] and lately A-site vacancies [12,13,14]. We show that carbon burial sintering is an effective and robust method for the preparation of SrTiO3-based ceramics, enabling further reduction of the material and enhancement of thermoelectric performance by an increase in carrier concentration
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