Single-crystal β-NiS nanorod arrays were in situ grown on a hollow structured Ni ₃ S ₂ porous framework by a facile one-step solvothermal approach, and finally the materials with a pine twig-like structure are constructed for high-performance electrode materials in supercapacitors.

We report a large electrocaloric effect with an adiabatic temperature change (ΔT) of 0.47 K under 20 kV cm⁻¹ combined with a broad temperature span (T_span) of 23 K within 90% ΔT (maximum) attenuation in a (Ba_0.87Ca_0.13)(Ti_0.87Hf_0.13)O₃ ceramic by indirect measurement. Here, in this (Ba_0.87Ca_0.13)(Ti_0.87Hf_0.13)O₃ ceramic, Ca²⁺ and Hf⁴⁺ are introduced into BaTiO₃ to obtain a multiphase coexisting region with a diffuse phase transition character. The large electrocaloric effect benefits from a larger number of possible equilibrium orientations of polar states due to multiphase coexistence, and the broad temperature span comes from the diffuse phase transition character. Compared to the control sample, BaTi_0.82Hf_0.18O₃ with only diffuse transition but no multiphase coexistence, (Ba_0.87Ca_0.13)(Ti_0.87Hf_0.13)O₃ displays a ΔT value nearly 1.5 times larger than that of BaTi_0.82Hf_0.18O₃ (ΔT ∼ 0.33 K), although they exhibit similar T_span values. Our work may shed light on developing high performance electrocaloric materials with broad temperature ranges.

Antiferroelectric thin films have demonstrated an excellent negative electrocaloric effect, and are potential candidates for future refrigeration applications. In this study, the electrocaloric effect of polycrystalline PbZrO₃ antiferroelectric thin films, deposited on Pt/Ti/SiO₂/Si substrates by a sol–gel method, were studied by an indirect method based on the Maxwell relations. It was found that the PbZrO₃ thin film undergoes a phase transition from the antiferroelectric to ferroelectric phase driven by the coupling of electric field and temperature. The antiferroelectric to ferroelectric transition leads to a giant negative electrocaloric effect in the PbZrO₃ thin film. It is also found that the phase transition temperature decreases with the increase in the applied electric field. As a result, the giant negative electrocaloric effect of the PbZrO₃ thin film could be tuned to room temperature, liquid nitrogen temperature and even down to liquid helium temperature range by applying different magnitudes of external fields. For instance, the maximum electrocaloric temperature change is −6.8 K at 292 K under 500 kV cm⁻¹, −6.7 K at 229 K under 600 kV cm⁻¹ and −3.8 K at 138 K under 700 kV cm⁻¹. Our results expand the working temperature of the electrocaloric materials into the ultra-low temperature range, and open up a new landscape for achieving low temperature cooling using ECE devices.