With the rapid development of wearable electronics, flexible and sensitive energy harvesters have recently attracted considerable attention. Herein, a novel piezo-triboelectric nanogenerator (PTNG) based on BCZT/PVDF-HFP composite nanofibers (BP-based NFs) is fabricated using silicone rubber as the negative triboelectric counterpart. The introduction of BCZT nanoparticles markedly improves both the piezoelectric and triboelectric properties of the BP-SG PTNG, where the output voltage and current density are 2.5–3 fold higher than those of pure PVDF-HFP PTNG. Owing to the uniform distribution of BCZT particles on the fiber surface via electrospinning, the maximum power density of the device reaches 161.7 mW m−2, representing 5.5-fold improvement compared to that of BaTiO3/PVDF-based composite PTNG. The device shows stable output for 1200 cycles and after three month storage and exhibits high sensitivity to minute body movements as proved by the output response in both two-electrode and single-electrode modes. This study demonstrates a novel approach to fabricate flexible PTNGs with simple structure and high sensitivity for use in self-powered wearable electronics.

Flexible composite-nanofiber based piezo-triboelectric nanogenerators for wearable electronics

The explosive process of 5G communication evokes the urgent demand of miniaturized and integrated dielectric ceramics filter. It is a pressing need to advance the development of dielectric ceramics utilization of emerging technology to design new materials and understand the polarization mechanism. This review provides the summary of the study of microwave dielectric ceramics (MWDCs) sintered higher than 1000 from 2010 up to now, °C with the purpose of taking a broad and historical view of these ceramics and illustrating research directions. To date, researchers endeavor to explain the structure-property relationship of ceramics with multitude of approaches and design a new formula or strategy to obtain excellent microwave dielectric properties. There are variety of factors that impact the permittivity, dielectric loss, and temperature stability of dielectric materials, covering intrinsic and extrinsic factors. Many of these factors are often intertwined, which can complicate new dielectric material discovery and the mechanism investigation. Because of the various ceramics systems, pseudo phase diagram was used to classify the dielectric materials based on the composition. In this review, the ceramics were firstly divided into ternary systems, and then brief description of the experimental probes and complementary theoretical methods that have been used to discern the intrinsic polarization mechanisms and the origin of intrinsic loss was mentioned. Finally, some perspectives on the future outlook for high-temperature MWDCs were offered based on the synthesis method, characterization techniques, and significant theory developments.

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The latest process and challenges of microwave dielectric ceramics based on pseudo phase diagrams

Characterization of Co0.5(Ti1-xZrx)0.5NbO4 Microwave Dielectric Ceramics Based on Structural Refinement

To enhance the piezoelectric responses, Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics were fabricated by a sol–gel method in various sintering atmospheres. The effects of oxygen partial pressure on the microstructure and electrical properties of BCZT ceramics were systematically investigated. The samples sintered in air, O2 and N2 are the coexistence of the orthorhombic (O)-tetragonal (T) phase at room temperature. The phase transition temperature of the O–T phase of BCZT samples sintered in air, O2 and N2 is gradually closer to room temperature. The results of EDS, XPS and the activation energy confirm the significant effect of oxygen sintering atmosphere. BCZT samples sintered in oxygen atmosphere show excellent ferroelectricity (2Pr = 31.62 μC/cm2, 2EC = 3.46 kV/cm) and significantly enhanced piezoelectricity (d33 = 604.3 pC/N, d
 33
 *
  = 647.5 pm/V and kp = 58%), resulting from the minimum oxygen vacancy, the phase transition temperature of O–T closer to room temperature and dense microstructure. These results demonstrate that adjusting oxygen partial pressure in sintering is an effective way to enhance the piezoelectric responses of BCZT ceramics.

Effects of oxygen partial pressure on the electrical properties and phase transitions in (Ba,Ca)(Ti,Zr)O3 ceramics

This study presents the microwave dielectric properties calculation of (1-x)Ba3.75Nd9.5Cr0.25Nb0.25Ti17.5O54–xNdAlO3 ceramics where x denotes the volume molar fraction. From X-ray diffraction results, the solid solution limit is calculated to be about 0.76, where it forms a single BaNd2Ti4O12 phase in Region I (0≤x<0.76), and both BaNd2Ti4O12 and NdAlO3 coexist in Region II (0.76≤x<1). The solid solution limit is confirmed by independently calculating it from the dielectric constant data. There is less than 4% deviation between the measured dielectric constant (er) and the one calculated from the Maxwell-Wagner formula. The total quality factor (Q) remains almost constant in Region I and increases rapidly with the volume molar fraction of NdAlO3 in Region II. The measured Q×f, where f is the resonant frequency, is also consistent with the calculated value in both regions. The temperature coefficient at the resonant frequency is −1.4 ppm/°C, which agrees well with the calculated value of 0 ppm/°C. In addition, we observed a close correlation between the bulk density and the phase evolution.

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Yingchun Zhang

Papers

Role of Cu and Y in sintering, phase transition, and electrical properties of BCZT lead-free piezoceramics

Microwave dielectric properties of (1−x)ZnTa2O6−xMgNb2O6 ceramics

Microstructure, hardness and toughness of boron carbide thin films deposited by pulse dc magnetron sputtering

Structure and properties of low temperature sintered ZnTa2O6 microwave dielectric ceramics