A-site defect construction in medium-entropy SrTiO3 ceramics for enhanced thermoelectric performance

The compositional flexibility and structural stability of SrTiO₃-based perovskite oxides present a promising approach to tailor their electrical and thermal transport properties. In this work, a series of (Ca_0.25Nd_0.25Sr_0.35Ba_0.15)_1-xTiO_3±δ ceramics with varying A-site deficiencies were designed by integrating entropy engineering and defect chemistry, and their microstructural characteristics and transport properties were systematically investigated. All samples exhibited a stable single-phase \(Pm\overline{3}m\) cubic structure with uniformly distributed constituent elements. The introduction of A-site vacancies created favorable pathways for ion diffusion during the sintering process and facilitated grain growth. A-site deficiencies significantly increased carrier concentration by promoting the formation of oxygen vacancies and Ti³⁺, while also enhancing carrier mobility by improving structural symmetry and reducing grain boundary scattering, leading to the improved power factor. The multiscale defects resulting from entropy engineering including point defects, strain fields, and high-density grain boundaries contributed to the reduced thermal conductivity of all samples. By synergistically optimizing the entropy and defect engineering, the sample with x = 0.09 achieved a peak figure of merit (ZT) of 0.21 at 900 K, representing a 32% enhancement compared with that of the x = 0.03 sample. This work underscores the significance of the combined strategy of entropy engineering and defect chemistry in manipulating the transport properties of SrTiO₃-based thermoelectric oxides.

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