The electricaloric refrigeration is based on the electricaloric effect due to its high energy conversion efficiency, environment friendly, small size and easy integration as a novel efficient refrigeration technology, which has become one of the emerging research hotspots in the field of ferroelectric. The solid solutions of 0.77NaNbO₃–0.23BaTiO₃+wMn (w=0, 0.2%, 0.4% and 0.6%, in mass fraction) electrocaloric ceramics were prepared by a conventional solid-state reaction method. The phase composition and microstructure of 0.77NaNbO₃–0.23BaTiO₃ ceramics with different Mn doping contents were characterized by X-ray diffraction and scanning electron microscopy. Meanwhile, the dielectric-temperature spectra, polarization electric field hysteresis loops and electrocaloric effect of the samples with different Mn doping contents were determined. The results indicate that Mn doped ceramics can promote the grain compaction, improve the dielectric constant and saturation polarization strength, reduce the dielectric loss, and enhance the electrocaloric effect. For the ceramic with Mn doping content w of 0.4%, ΔT=0.39 K, and ΔS=0.71 J·kg^–1·K^–1, the electrocaloric strength of ΔT/ΔE enhances from 0.05×10^–6 K·m·V^–1 to 0.13×10^–6 K·m·V^–1, and ΔS/ΔE enhances from 0.08×10^–6 K m·V^–1 to 0.24×10^–6 J·m·kg^–1·K^–1·V^–1 under 30 kV·cm^–1 at room temperature. It is indicated that 0.77NaNbO₃–0.23BaTiO₃+0.4%Mn ceramic could be used as an promising electrocaloric refrigeration material.

Integrated sensor combines multiple sensor functions into a single unit, which has the advantages of miniaturization and better application potential. However, limited by the sensing platforms of the sensor and the selectivity of the sensitive film, there are still challenges to realize multi-component gas detection in one unit. Herein, a principle integration method is proposed to achieve the multi-component gas detection based on the acoustics-electricity-mechanics coupling effect. The electrical and mechanical properties of the Bi₂S₃ nanobelts materials in different atmospheres indicate the possibility of realizing the principle integration. At the same time, the surface acoustic wave (SAW) sensor as a multivariable physical transducer can sense both electrical and mechanical properties. Upon exposure to 10 ppm NO₂, NH₃, and their mixtures, the integrated SAW gas sensor shows a 4.5 kHz positive frequency shift (acoustoelectric effect), an 11 kHz negative frequency shift (mechanics effects), and a reduced 4 kHz negative frequency shift (acoustics-electricity-mechanics coupling effect), respectively. Moreover, we realize wireless passive detection of NO₂ and NH₃ based on the SAW sensor. Our work provides valuable insights that can serve as a guide to the design and fabrication of single sensors offering multi-component gas detection via different gas sensing mechanisms.

Electrocaloric effect, i.e., the entropy and temperature changes arising from phase transition and dipole orientation induced in electric fields, can realize heat transport and refrigeration. The electrocaloric cooling eliminates the use of environmentally harmful coolants, possesses high cooling efficiency, small size and low weight as a promising environmental-friendly and high-efficiency cooling. One key point for electrocaloric cooling toward practical cooling is to enhance the performance of the electrocaloric effect of ferroelectrics. Ferroelectric ceramics have attracted much attention due to their high polarization, rich phase structures and variety of regulation methods. In this review, we introduced the electrocaloric effect of ferroelectric ceramic thin films, bulks and multilayer thick films with various compositions, and discussed the internal relations among electrocaloric effect, compositions, phase transition behaviors and microstructures. Furthermore, we concluded the modulation approaches of the electrocaloric effect of ferroelectric ceramics, and gave the future development of electrocaloric materials.