Sintering-activated grain boundary–porosity synergy: A new frontier for thermoelectric optimization in CaMnO₃

Perovskite oxides such as CaMnO₃ represent promising, eco-friendly thermoelectric alternatives to toxic chalcogenides, yet their performance remains constrained by the inherent resistivity–Seebeck trade-off and high lattice thermal conductivity (κ_L) from strong Mn–O bonding. This study pioneers a sintering-driven microstructure engineering strategy to decouple electron–phonon transport in CaMnO₃. By optimizing sintering parameters (temperature: 1473–1548K; duration: 2–10h), we achieve grain coarsening (1.34→2.46 μm) and porosity reduction, breaking the conventional performance limits. The engineered microstructure exhibits remarkable carrier-weighted mobility (μ_w) of 13.96cm²⋅V⁻¹⋅s⁻¹ and low κL=1.537W⋅m⁻¹⋅K⁻¹ at 973K, synergistically boosting the power factor by 127% (2.227 μW⋅cm⁻¹⋅K⁻²) and attaining a peak zT of 0.13 — the highest reported value for pristine CaMnO₃ thermoelectrics to date. Crucially, we identify 1548K/4 h as the kinetic threshold for balanced grain growth and densification, stabilizing microstructures (<5% property variation) for industrial scalability. This work establishes a universal sintering–structure–property paradigm to advance perovskite thermoelectrics toward sustainable energy applications.