Electrocaloric effect (ECE) in ferroelectric (FE)/antiferroelectric (AFE) materials offers a promising high-efficient and zero-emission solid-state cooling technology, whose materials design is usually focused on the morphotropic phase boundary (MPB) between two FE phases. This work constructs an MPB between an orthorhombic AFE and a rhombohedral FE phase in Pb 0.97−x Ba x La 0.02 Zr 0.95 Ti 0.05 O 3 (PBLZT100x, x = 0−0.08) ceramics and achieves a superior ECE performance. An unprecedented high electrocaloric strength of 1.52 K•mm/kV and an ultrahigh refrigeration efficiency (coefficient of performance = 16) are obtained in PBLZT4, in the MPB near AFE end. Moreover, a large negative ECE, with the highest strength up to −0.41 K•mm/kV, is also realized due to the electric field-induced AFE−FE transition. The coexistence of giant positive and negative ECEs at adjacent temperatures can further improve the cooling capacity (∼17%) of solidstate refrigeration in a well-designed cooling cycle. This work provides a brand new materials design strategy to achieve giant positive and negative ECEs simultaneously and a novel cooling cycle to efficiently utilize the two effects.
As an emerging solid‐state refrigeration technology with zero‐emission and high energy conversion efficiency, there is a compelling need for ferroelectric materials with giant electrocaloric effects (ECEs) at room temperature suitable for refrigeration applications. The complex perovskite antiferroelectric (AFE), PbMg0.5W0.5O3, containing non‐equivalent B‐site ions with a symmetric giant positive and negative ECE near room temperature is presented. At the Curie temperature of 36 °C, the first‐order AFE–paraelectric phase transition gives rise to a large enthalpy change of 3.92 J g−1, more than four times that of BaTiO3. This leads to a significant ECE under the influence of an electric field. The direct electrocaloric characterization shows that the adiabatic temperature change, ΔT, exhibits symmetric peaks with a giant positive maximum of 1.79 K (ΔS = 1.68 J kg−1 K−1) at 36 °C and a negative maximum of −2.02 K (ΔS = −1.93 J kg−1 K−1) at 34 °C. The ultrahigh magnitude of ΔT near room temperature makes PbMg0.5W0.5O3 a superior electrocaloric material far beyond traditional PbZrO3‐based AFEs. The coexistence of symmetric giant positive and negative ΔT to further improve cooling efficiency is expected. In addition, the good reversibility and negligible leakage current should pave the way for practical applications.
An outstanding challenge for high‐efficient and zero‐emissions ferroelectric refrigeration is to maintain a large adiabatic temperature change (ΔT) over a wide temperature span (Tspan) resulting from the electrocaloric effect (ECE). A multilayer ferroelectric structure with interlayer synergistic phase transitions as a means to address this problem is proposed. BaTi0.89Sn0.11O3, BaTi0.85Zr0.15O3, and BaTi0.89Hf0.11O3 were selected as the components of each layer, the compositions of which are fixed at the tricritical point (TP) in each system and where the transition temperatures increase sequentially. Ferroelectrics near TP have a high sensitivity to external fields and the good co‐firing adhesion leads to strong electrical and stress interface coupling between adjacent layers. The electric‐field‐induced phase transition in one layer then synergistically induces a phase transition in the near interface part of the adjacent layer, which is close to but is not at the transition point yet. As a result, the enhanced ECE performance, including both a large ΔTmax = 0.63 K and a wide Tspan = 57 °C (ΔT ≥ 80% ΔTmax), exceeds that associated with the sum of the individual components. An efficient composite materials design strategy to develop high‐performance electrocaloric materials with excellent ECE properties for practical refrigeration applications is thus proposed.
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