Tuning the site occupancy and valence state of Mn to enhance electrocaloric performance of Ba0.9Sr0.1Ti0.9Zr0.1O3 ceramics

Electrocaloric (EC) refrigeration offers a promising alternative to conventional vapor-compression systems by eliminating greenhouse‑gas refrigerants and achieving high efficiency through reversible polarization switching. In this work, Ba 0.9 Sr 0.1 Ti 0.9 Zr 0.1 O 3 – x wt% MnO 2 ( x  = 0–0.4) (BSZT) ceramics were prepared by the solid‑state sintering method to investigate the effects of MnO 2 doping on the phase structure, microstructure, ferroelectric properties, and EC performance. During the sintering process, MnO 2 doping not only provides a sintering‑aid effect, but also generates oxygen vacancies ( V O •• ) due to the substitution of Mn 3+ /Mn 2+ for Ti 4+ . As a result, the defect dipoles Mn 3+ /Mn 2+ - V O •• , together with the sintering‑aid effect, promote grain growth. Mn 3+ /Mn 2+ were further suggested to occupy the B sites and increase the cation disorder, which tailors the relaxor behavior and electrical properties. As a result, the maximum polarization ( P max ) under 60 kV/cm increases from 18.2 μC/cm² to 20.2 μC/cm² at a MnO 2 content of 0.3 wt%. An adiabatic temperature change Δ T max of 1.41 K was achieved at 60 kV/cm. However, excessive MnO 2 doping suppresses grain growth and deteriorates the ferroelectric and EC properties. Therefore, the appropriate introduction of MnO 2 into BSZT is an effective strategy for enhancing EC performance.