In-situ construction of all-scale hierarchical microstructure and thermoelectric properties of (Sr0.25Ca0.25Ba0.25La0.25)TiO3/Pb@Bi composite oxide ceramics

SrTiO3-based oxides have been investigated as a promising n-type thermoelectric material at high temperatures; however, the relatively high thermal conductivity results in inferior thermoelectric performance. The lattice thermal conductivity can be significantly reduced by high-entropy engineering via severe lattice distortion. However, high configuration entropy also causes the deterioration of carrier mobility and restrains electron transport resulting in low electrical conductivity. In this work, the low lattice thermal conductivity of 1.7 W/(m$K) at 1 073 K and significantly improved electrical conductivity of 112 S/cm from 60 S/cm can be achieved in n-type (Sr0.25Ca0.25Ba0.25La0.25)TiO3/Pb@Bi composites ceramics with core-shell grains of all-scale hierarchical microstructure. The effects of the complex microstructure of core-shell grains as well as the precipitated Pb@Bi particles on electrons and phonons transport properties were systematically explored. ZTmaxof 0.18 was obtained for the SPS-120 0, which was 1.5 times that of pure high-entropy (Ca0.2Sr0.2Ba0.2La0.2Pb0.2)TiO3 samples prepared by a solid-state method. This improvement in thermoelectric performance contributes to the addition of Bi2O3 into the high-entropy (Sr0.2Ca0.2Ba0.2Pb0.2La0.2)TiO3 matrix resulting in multiphase core-shell grain structure combined with well-dispersed nano-sized metal Pb@Bi precipitates in the matrix. This feasible strategy of in-situ constructing all-scale hierarchical nanostructures can also be applied to enhance the performance of other thermoelectric systems.