High Thermoelectric Performance in n-Type CaTiO3 Compounds Enabled by Weakened Carrier–Phonon Coupling

Calcium titanite, as an eco-friendly thermoelectric material, offers great potential for thermoelectric power generation. However, the polar metal–oxygen bonds place a low ceiling on the electrical conductivity, thereby limiting the overall thermoelectric performance. In this work, high-purity Ca 1- x Pr x Ti 0.95 Nb 0.05 O 3 ( x = 0–0.20) compounds are synthesized to investigate the electrical and thermal transport features. Nb doping enhances bond covalency, as confirmed by electron localization function (ELF) and crystal orbital Hamilton population (COHP) analyses. This enhancement leads to high carrier mobility by weakening the electron–phonon coupling, a mechanism verified by direct electron–phonon coupling calculations. Meanwhile, the multiscale hierarchical architectures, including dual point defects, nanoprecipitates, dislocations, etc., originating from the large mass and strain field fluctuations, further reduce the lattice thermal conductivity close to the minimum value estimated from Cahill's model. A peak ZT value of 0.33 is acquired for Ca 0.90 Pr 0.10 Ti 0.95 Nb 0.05 O 3 at 1073 K, approximately 267% higher than that of the pristine CaTiO 3 sample. Our investigation highlights that weakening the carrier–phonon coupling by modulating chemical bonding is a reasonable strategy, which could be applied in other thermoelectric systems.