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

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 represent promising candidates for multicaloric cooling. In this work, the idea to prepare such material is to tailor the temperature of the ferroic anomalies by introducing BiFeO3, a material possessing high-temperature ferroic phase transitions, into the multicaloric Pb(Fe0.5Nb0.5)O3 to form a solid solution. A series of (1-x)Pb(Fe0.5Nb0.5)O3–xBiFeO3 (x = 0–0.5) were prepared. Among them, 0.8Pb(Fe0.5Nb0.5)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 low magnetocaloric response. Because of that, the multicaloric properties of 0.8Pb(Fe0.5Nb0.5)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 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(Fe0.5Nb0.5)O3-based multicalorics.