Electrocaloric Effect of Perovskite High Entropy Oxide Films.

This paper describes two perovskite high entropy oxide (PHEO) compositions: Pb(Hf0.2Zr0.2Ti0.2Nb0.2Mn0.2)O3 (Mn PHEO) and Pb(Hf0.2Zr0.2Ti0.2Nb0.2Al0.2)O3 (Al PHEO). Powders are prepared by conventional solid state sintering by first pre‐reacting the B‐site oxides, then adding PbO. Phase pure Mn PHEO powder is obtained following calcination of the mixed powders at 750 °C for 240 min; however, secondary phases persisted in Al PHEO for heat treatments from 750 °C to 1200 °C. The Mn PHEO undergoes an entropy‐driven phase transformation. Thin films of these compounds are synthesized by pulsed laser deposition (PLD) on a lead zirconate titanate seed layer on Pt‐coated SiO2/Si. The dielectric response of the Mn PHEO films show some contribution from space charge polarizability; in contrast, the Al PHEO films show a slim ferroelectric hysteresis loop and relaxor‐like characteristics. The Al PHEO has a dielectric permittivity of ≈2000 with a loss tangent <0.05 from 100 Hz to 100 kHz; it has a dielectric maximum at 105 ± 0.5 °C and a Burns' temperature of 234 ± 0.5 °C. Indirect measurements based on the Maxwell‐relations yielded a maximum electrocaloric temperature change of 8.4 K at 180 °C under the applied electric field of 1186 kV cm−1. [ABSTRACT FROM AUTHOR]