Electrocaloric effect in strained bismuth ferrite under bipolar field

Ferroic materials with multiple order parameters hold promise for enhanced electrocaloric effect (ECE), but the existence of some order parameters can be detrimental, such as octahedral tiltings in perovskites that are coupled competitively with polarization. In multiferroic ${\mathrm{BiFeO}}_{3}$, the magnitude of the antiphase octahedral tilting can be tuned by the application of a biaxial strain, in particular that the tilting can be completely annihilated in the super-tetragonal phase ($T$ phase). Here, we study the ECE of strained $R3c$ and $T$ phases of ${\mathrm{BiFeO}}_{3}$ using an effective Hamiltonian approach. ECE in the $T$ phase is indeed found to be improved compared with that of the $R3c$ phase. The effects of strain on the adiabatic temperature change in both phases under bipolar fields in [001] and $[00\overline{1}]$ directions, as well as the ECE associated with polarization switching, are reported in details.