Entropy Manipulation of SrTiO₃ Perovskite for Enhanced Thermoelectric and Mechanical Properties

Reducing the thermal conductivity while maintaining excellent electrical transport properties is crucial for enhancing the thermoelectric performance of SrTiO₃-based perovskites. Here, we successfully achieved this goal through precisely manipulating the configurational entropy. A series of Ca_0.25Nd_0.25Sr_0.5- BaTiO₃ (x = 0, 0.05, 0.15, 0.25) ceramics were successfully synthesized using the solid-state reaction combined with graphite burial sintering. It was discovered that structural defects from competing elements in the A-site not only slowed diffusion and hindered grain growth but also increased oxygen vacancies by creating additional gas transmission channels. The gradual decrease in carrier mobility with increasing entropy resulted in the degradation of electrical conductivity, while the Seebeck coefficient experienced a large enhancement due to band modification and increased carrier scattering. Meanwhile, multiscale defects, including point defects, local strain fields, dislocations, and grain boundaries, effectively scatter phonons, leading to a low lattice thermal conductivity of 1.73 W·m^-1·K^-1. Consequently, the sample with x = 0.15 exhibited a peak ZT of 0.15 at 900 K, reflecting a 148% enhancement compared to that of the matrix. In addition, the hardness increases with configurational entropy because of the chemical disorder, grain refinement, and increased defect concentration. The work emphasizes the importance of precise manipulation of configurational entropy, offering valuable insights for optimizing thermoelectric materials through entropy engineering strategy.