Enhanced electrocaloric effect in compositional driven potassium sodium niobate‐based relaxor ferroelectrics

Abstract

Lead-free ferroelectric electrocaloric ceramics that could convert electrical energy into heat are the promising candidate for environment-friendly cooling devices. For refrigeration devices, a large temperature change (ΔT ) and good temperature stability are required, which are highly related to the phase structure and the applied electric field. In this work, a diffused ferroelectric-paraelectric (FP) phase transition is formed in (K, Na)NbO 3 (KNN) by using appropriate composition engineering. The relaxor ferroelectrics in this work present both a large ΔT of 1.24 K and a high ΔT/ΔE of 0.19 K mm/kV. In addition, a wide temperature span exceeds 55°C at the high electrocaloric effect (ECE) criterion (ΔT ≥ 0.5 K) could also be observed. This work not only opens a new strategy for obtaining high-performance ceramics for refrigeration devices but also extends the application area of the KNN-based lead-free ferroelectrics from sensors, actuators and energy harvesting to solid-state cooling applications.

Large electrocaloric effect under electric field behavior in potassium sodium niobate ceramics with incompletely overlapped phase boundaries

“…The promoted ECE performance is mainly due to the synergetic contribution of initially incompletely overlapped phase boundaries and high E for the ceramics. 39,[46][47][48][49][50][51] The metastable ferroelectric transition process always leads to increased energy barrier, meaning larger E. In addition, much higher E CE ($100 kV cm À1 ) could be inferred at 70 C for x ¼ 0.05 and 0.06 because of their comparatively higher E C and main process of domain switching.…”

“…9(d) and (e) present the operating temperature and T span of the optimized DT in the ceramics compared with other KNNbased ceramics when DE < 150 kV cm À1 , respectively. Notably, large DT as well as low operating temperature and broad T span is achieved in the ceramics simultaneously, realizing a comprehensive improvement for ECE in KNN-based ceramics 39,[46][47][48][49][50][51].…”

Enhanced electrocaloric effect, energy storage density and pyroelectric response from a domain-engineered lead-free BaTi0.91Sn0.08Zr0.01O3 ferroelectric ceramic

“…9(a). The heat, Q , and subsequently Δ S and Δ T were calculated from the area under the exothermic and endothermic peaks using the following formulas: 79,80 …”

Enhanced Electrocaloric Effect Induced by the Electric-Field-Generated Like-Multiphase Coexistence in Anisotropic KTa1–xNbxO3 Single Crystals

“…Based on the Maxwell relationship, (∂ P /∂ T ) E = (∂ S /∂ E ) T , thermal variables and electrical parameters were linked. Nowadays, the indirect method of calculating Δ T of ECE is widely used in many piezoelectric materials, such as PZT, , PMN-PT, , BT, ,, and (K 1– x Na x )­NbO 3 (KNN). , Δ T can be calculated using where P , ρ, and C P are the polarization vectors, density, and specific heat capacity, respectively.…”