Pb(Fe0.5Nb0.5)O3–BiFeO3-based multicalorics with room-temperature ferroic anomalies

Abstract

The search for new single-phase multicaloric materials, combining electrocaloric and magnetocaloric effects, is just at its beginning. Since the highest caloric effects are obtained near ferroic phase transitions, multiferroics with room-temperature ferroic anomalies are promising candidates for multicaloric cooling. In this work, such materials were prepared by tailoring the temperature of the ferroic anomalies by introducing BiFeO₃, a material possessing high-temperature ferroic phase transitions, into the multicaloric Pb(Fe_0.5Nb_0.5)O₃ to form a solid solution. A series of (1−x)Pb(Fe_0.5Nb_0.5)O₃–xBiFeO₃ (x = 0–0.5) were prepared. Among them, 0.8Pb(Fe_0.5Nb_0.5)O₃–0.2BiFeO₃ exhibits both dielectric permittivity and magnetic susceptibility anomalies at room temperature and is therefore one of the first such single-phase materials. However, at higher temperatures the material exhibits excessive Joule heating that critically degrades the electrocaloric cooling effect, while the antiferromagnetic nature of the material results in a low magnetocaloric response. Because of that, the multicaloric properties of 0.8Pb(Fe_0.5Nb_0.5)O₃–0.2BiFeO₃ were further improved by doping the material with Mn and Gd ions. This results in a composition with negligible Joule heating up to 75 °C and with room-temperature electrocaloric effect of more than 1 °C, and a high magnetocaloric effect of ∼3 °C at cryogenic temperatures. Furthermore, this material also exhibits the highest room-temperature magnetocaloric effect (∼8 × 10⁻³ °C) among all already known Pb(Fe_0.5Nb_0.5)O₃-based multicalorics.