Atomic-scale B-site deficiency stabilizes enhanced thermoelectric properties of calcium manganese oxides

Abstract

Doping CaMnO₃ ceramics with rare earth ions at A-sites and transition metal ions at B-sites optimizes carrier transport and enhances phonon scattering. However, single cationic regulation shows limited thermoelectric improvement. Introducing Ti non-stoichiometric doping creates vacancy defects, systematically affecting microstructure, resistivity, and thermal conductivity. The twin-boundary shear and several lattice defects were nucleated from the free surface and propagated parallel to grain boundaries. Mn vacancies ("V" _"Mn" ^"''''" /"V" _"Mn" ^"'''" ) and O vacancies (V_O^(··)) induce electrostatic interactions, suppress carrier scattering, and act as phonon scattering centers, reducing lattice thermal conductivity. The x=0.07 sample achieved minimal ρ (22.49 mΩ·cm) at 1073 K, yielding a maximum ZT of 0.14 and quality factor of 5.3×10⁻² due to vacancy and electronic compensation synergy. The B-site vacancy deficiency points toward the way to tunable and possibly electron and phonon transporting behavior, which is benefit for the thermoelectric performance of oxyselenides thermoelectric ceramics.