Abstract
A large electrocaloric effect is reported in a strain-engineered Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) thin film heterostructure driven by the near room-temperature electro-structural phase transition. An epitaxial BCZT/La0.7Sr0.3MnO3 (BCZT/LSMO) heterostructure was grown on a 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 an unprecedently large adiabatic temperature change of 13.5 K at 430 K under a field change of 1000 kV cm−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 a large electrocaloric effect in the lead-free BCZT thin film may open up new pathways toward the design of artificial heterostructures for eco-friendly solid-state cooling applications.
Highlights
Electrocaloric (EC) effects of large thermal changes across the phase transitions in ferroelectric (FE) materials when subjected to electric field stimuli promise eco-friendly and energy-efficient solidstate cooling technologies.1–4 Theoretically, the choice of an idealEC material depends on the parameters that quantify EC effects, namely, the adiabatic temperature change ΔT and the isothermal entropy change ΔS
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
We propose that an interfacial strain-induced enhanced tetragonal distortion of the BCZT layer gives rise to these hitherto unobserved enhanced EC effects in the BCZT/LSMO heterostructure system
Summary
Electrocaloric (EC) effects of large thermal changes across the phase transitions in ferroelectric (FE) materials when subjected to electric field stimuli promise eco-friendly and energy-efficient solidstate cooling technologies. Theoretically, the choice of an ideal. In terms of lead-free FE materials, the perovskite oxide, Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT), is promising due to its significant dielectric properties (dielectric constant ∼3000 to 8000) and ferroelectric properties (remanent polarization Pr ≈ 10 μC cm−2 –15 μC cm−2 and coercive field EC ≈ 1.5 kV cm−1–3 kV cm−1) near room temperature, in combination with a large piezoelectric coefficient (≈620 pCN−1), which is comparable to lead-based PbxZr1−xTiO3 (PZT) materials.. We report the observation of a large EC effect (∣∆T∣ = 13.5 K under ∣∆E∣ = 1000 kV cm−1 at 430 K) across the ferroelectric–paraelectric phase transition in the lead-free perovskite BCZT thin film. Cross-sectional electron microscopy imaging revealed the cube-on-cube epitaxial growth and defect-free interfaces in the BCZT/LSMO heterostructure Both temperature dependent x-ray diffraction and dielectric measurements revealed a broad electrostructural phase transition near 430 K in the BCZT/LSMO heterostructure. In epitaxial lead-free thin films and provides a key insight into the design of artificial heterostructures with novel and enhanced EC properties
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