Reduced lattice thermal conductivity of perovskite-type high-entropy (Ca0.25Sr0.25Ba0.25RE0.25)TiO3 ceramics by phonon engineering for thermoelectric applications

The high-entropy effect suggests the possibility of unusual thermal transport properties that may be favorable for thermoelectrics. Novel perovskite-type high-entropy (Ca0.25Sr0.25Ba0.25La0.25)TiO3 (4La) and (Ca0.25Sr0.25Ba0.25Ce0.25)TiO3 (4Ce) ceramics were successfully prepared through a conventional solid-state reaction method. XRD, SEM-EDS, and HRTEM were performed to confirm that the chosen multi-component cations can be introduced into A-site to form a single cubic phase with Pm-3m space group. Introduce high-entropy engineering, constituent elements competing inter into the A-site creating lattice distortion and strain fields, which results in extensive structural defects including dislocations which contributed to the phonons scattering of mid wavelength. Grain boundaries and intrinsic oxygen vacancies respectively scatter phonons of high and low wavelengths. The enhanced effective scattering of phonons through the multi-scale defects gives rise to a low lattice thermal conductivity of 2.5 W·m−1·K−1 at 1073 K for the 4La ceramics, much lower than that of SrTiO3-based perovskite thermoelectric ceramics. The high-entropy 4La ceramics possess the maximum power factor of 420 μW·m−1·K−2. This work provides a strategy of compositional design for thermoelectric oxides with decreased intrinsic thermal conductivity for thermoelectric applications.