Large electrocaloric effect in lead-free ferroelectric Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ thin film heterostructure

A large electrocaloric effect is reported in a strain-engineered Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ (BCZT) thin film heterostructure driven by the near room-temperature electro-structural phase transition. An epitaxial BCZT/La_0.7Sr_0.3MnO₃ (BCZT/LSMO) heterostructure was grown on single-crystal SrTiO₃ (100) substrate using pulsed laser deposition. In-depth x-ray diffraction and x-ray spectroscopic analyses revealed the single-crystalline nature and stoichiometric growth of the heterostructure. Both temperature dependent x-ray diffraction and dielectric measurements revealed a broad second-order-type phase transition near 430 K in the BCZT/LSMO heterostructure. From detailed theoretical analyses of the experimental data it was confirmed that the phase transition around 430 K is second-order in nature, unlike the first order transition observed in bulk BCZT materials. Thermodynamic analyses of polarization revealed unprecedently large adiabatic temperature change of 13.5 K at 430 K under a field change of 1000 kVcm^-1 ; hitherto unobserved in a lead-free material. Extremely broad adiabatic temperature change ΔT(T) curves over a wide working range of temperatures (330 K < T < 480 K) resulted in enhanced relative cooling powers which are higher than those reported so far in most electrocaloric materials. We propose that an interfacial strain-induced enhanced tetragonal distortion of the BCZT layer gives rise to these large electrocaloric effects in the BCZT/LSMO heterostructure system. The demonstration of large electrocaloric effect in the lead-free BCZT thin film may open up new pathways towards the design of artificial heterostructures for eco-friendly solid-state cooling applications.