Thermoelectric enhancement in perovskite type textured Me0.85TiO3 ceramics by synergistic high-entropy and microstructure manipulations

Abstract

Enhancing the figure-of-merit (ZT) for thermoelectric ceramics essentially needs strategies that aim to concurrently optimize electron and phonon transport properties to decouple their coupling relationship. This work developed 〈001〉 -textured Me0.85TiO3(Me = La, Sr, Ba, Ca) ceramics (LSBC-T) with a texture fraction of 92 % fabricated by a tape casting process combined with template grain-growth method, in which 10 wt% (001) oriented plate-like SrTiO3 serves as template seed and A-site deficient high-entropy (La0.25Sr0.25Ba0.25Ca0.25)0.85TiO3 composite was used as matrix material. A peak ZT of 0.27 was attained at 1073 K in the sample parallel to the tape casting direction which was twice the ZT = 0.13 of the non-textured sample. Quantitative analysis of atomic displacement disorder of A-site elements would provide an atomistic-scale understanding of grain orientation evolution with high texture degree and the low thermal conductivity of 1.79 W/(m‧K) at 1073 K. The complex multi-scale defects consist of cation and oxygen vacancies, edge dislocations, parallel grain boundaries, phase interfaces, nanoscale metal/inorganic coexisting clusters, and metal Bi sandwich layer, which act as additional phonon scattering centers while affecting carrier transport, covering all frequency phonons (100 GHz-15 THz). In addition, multi-scale parallel interfaces, including atomic-scale crystal (00l) plane of SrTiO3 seed, nano-scale “core-shell” interface parallel to the (00l) plane, metal Bi particle forming a sandwich layer in SrTiO3 seed, and “brick-wall” textured grain boundaries, make the electrical and thermal conductivity exhibiting obvious anisotropy in this LSBC-T high-entropy textured ceramics. By utilizing texture engineering in high-entropy systems, this work provides a theoretical foundation and technical support for the advancement of microstructure manipulations to reduce the inherent lattice thermal conductivity, achieve electrical and thermal conductivity anisotropy to decouple the electron–phonon coupling relationship, and thereby enhance thermoelectric properties.