State transition and electrocaloric effect of BaZr_xTi_1−xO₃: Simulation and experiment

We present a systematic study on the relation of the electrocaloric effect (ECE) and the relaxor state transition of BaZr_xTi_1−xO₃ (BZT) using a combination of computer simulation and experiment. The results of canonical and microcanonical lattice-based Monte Carlo simulations with a Ginzburg-Landau-type Hamiltonian are compared with measurements of BaZr_xTi_1−xO₃ (x = 0.12 and 0.2) samples. In particular, we study the ECE at various temperatures, domain patterns by piezoresponse force microscopy at room temperature, and the P-E loops at various temperatures. We find three distinct regimes depending on the Zr-concentration. In the compositional range $0≤x≤0.2$⁠, ferroelectric domains are visible, but the ECE peak drops considerably with increasing Zr-concentration. In the range $0.3≤x≤0.7$⁠, relaxor features become prominent, and the decrease in the ECE with Zr-concentration is moderate. In the range of high concentrations, $x≥0.8$⁠, the material is almost nonpolar, and there is no ECE peak visible. Our results reveal that BZT with a Zr-concentration around $x=0.12∼0.3$ exhibits a relatively large ECE in a wide temperature range at rather low temperature.