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Piezoelectric energy harvesting has attracted significant attention in recent years due to their high-power density and potential applications for self-powered sensor networks. In comparison to dense piezoelectric ceramics, porous piezoelectric ceramics exhibit superiority due to an enhancement of piezoelectric energy harvesting figure of merit. This paper provides a detailed examination of the effect of pore morphology on the piezoelectric energy harvesting performance of porous barium calcium zirconate titanate 0.5Ba(Zr0.2 Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) ceramics. Three different pore morphologies of spherical, elliptical, and aligned lamellar pores were created via the burnt-out polymer spheres method and freeze casting. The relative permittivity decreased with increasing porosity volume fraction for all porous BCZT ceramics. Both experimental and simulation results demonstrate that porous BCZT ceramics with aligned lamellar pores exhibit a higher remanent polarization. The longitudinal d33 piezoelectric charge coefficient decreased with increasing porosity volume fraction for the porous ceramics with three different pore morphologies; however, the rate of decrease in d33 with porosity is slower for aligned lamellar pores, leading to the highest piezoelectric energy harvesting figure of merit. Moreover, the peak power density of porous BCZT ceramics with aligned lamellar pores is shown to reach up to 38 μW cm-2 when used as an energy harvester, which is significantly higher than that of porous BCZT ceramics with spherical or elliptical pores. This work is beneficial for the design and manufacture of porous ferroelectric materials in devices for piezoelectric energy harvesting applications.

The low energy density of polymer-based dielectrics greatly limits their application in electronic components. Constructing composites with two-dimensional ceramic fillers is considered an effectiv...

Refractory lining is an important part of microwave heating equipment, and its wave-transparent effect significantly influences microwave heating efficiency. The complex dielectric constant of the material is the main factor determining its wave-transparent properties. In this study, with aluminium silicate fibreboard (ASF) as the study object, the complex dielectric constant of this material was investigated at temperatures ranging from 25 °C to 1000 °C at 915 MHz and 2450 MHz, respectively. Based on the theory of transmission lines, the wave-transparent properties of the material during the entire microwave heating process were calculated and analysed. It has been found that the dielectric constant and loss factor at both frequencies increase significantly when the temperature exceeds 700 °C; the wave-transparent properties of this material decrease with increasing temperature and present a fluctuating trend as the material thickness increases, with maximum and minimum values; in TM polarization mode, there is an optimal angle of incidence for total transmission, which contributes to a better overall wave-transparent effect of the material in TM polarization mode than that in TE polarization mode. Finally, this study provides the preferred thickness values at different working frequencies and temperatures under vertical incidence of electromagnetic waves for reference. This study is of certain theoretical significance to the research on the change mechanism of the material's dielectric and wave-transparent properties and has practical guidance on the optimization of microwave heating equipment and the selection of the technological parameters of furnace linings.

Dielectric polymer materials have received increasing attention in the electronic and electrical industries, however, the miniaturization and intelligent applications of polymer capacitors are limited due to their low energy density. Recently, the construction of sandwich structured films provides a good pathway to improve the energy storage performance of dielectric polymers. In this research, all-organic sandwich structured dielectric polymer films consisting of linear dielectric and ferroelectric polymers are proposed and successfully made by simple layer-by-layer solution casting. Theoretically, the ferroelectric poly(vinylidene fluoride–trifluoroethylene–chlorotrifluoroethylene) (PVTC) layer can enhance the dielectric displacement because of high dielectric constant, while the polyetherimide (PEI) layers can raise the operating temperature, owing to the high glass transition temperature, and increase the breakdown strength (Eb) and reduce the loss due to their linear characteristic. Therefore, a series of positive-sandwich structured films (with the central PVTC layer and the outer PEI layers), reverse-sandwich structured films and single-layered blend films are fabricated for optimization and comparison. The influence of the linear/ferroelectric volume ratio and the polymer film structure on the energy storage performance has been thoroughly researched. Experimental results showed that the all-organic positive-sandwich structured film with an optimized low content ratio of PVTC can endure a highest Eb of 530 kV mm−1 and exhibits a maximum discharge energy density of 8.0 J cm−3, which was more than two times that of the pure PEI film. Furthermore, the efficiency was up to 81%. More importantly, it possesses excellent temperature stability of the dielectric and energy storage properties from 25 °C to 100 °C. This work provides theoretical analysis and experimental guidance for the fabrication of all-organic sandwich structured films with high energy storage performance, which promotes the development and application of flexible polymer high temperature dielectric capacitors.

Piezoelectric materials were proven as a promising candidate to improve the efficiency of photocatalysis degradation activity via preventing the recombination of photoelectron–holes by stress-induced electric potential. In this work, core–shell structured catalytic agents consisting of lead-free piezoelectric ceramics Bi0.5Na0.5TiO3 (BNT) and photoelectric materials BiVO4 (BVO) were prepared by a hydrothermal method. The BNT@BVO powders were employed in the degradation of organic dye Rhodamine B (RhB) and exhibited superior catalytic activity due to the piezo-photoelectronic coupling effect. High first-order rate constants k of 0.110 min−1 and 0.045 min−1 were achieved for RhB solution with the initial concentrations of C0 = 5 mg L−1 and 10 mg L−1, respectively. To overcome the difficulties of powder recovery in applications, a series of macroscopic cloths with different BNT@BVO filler loadings and thicknesses were fabricated via an electrostatic spinning route. The degradation efficiency of RhB solution (C0 = 10 mg L−1) by a piece of BNT@BVO cloth (∼50 cm2) reached 80% in 100 min with a first-order rate constant of 0.015 min−1. In order to reveal the charge transfer mechanism in the interface layer between piezoelectric materials and photoelectric materials, a series of photoelectrochemical measurements were carried out. The conduction band (CB) position of BNT was bent from −1.1 eV towards −0.8 eV after being coated with BVO, which means less energy was required to be absorbed for the charge transition from the valence band (VB) to CB for the BNT and BNT@BVO have the same VB, resulting in a higher electron–hole separation efficiency. The enhancement of current density after coating with BVO from 2.3 μA cm−2 to 4.9 μA cm−2 (about 110% higher than that of pure BNT) at a potential of 1.23 V (vs. RHE) further verifies that the coupling between BNT and BVO has significant influence on charge separation efficiency.

Refractory lining is an indispensable part of high temperature microwave heating equipment, and its wave transmission performance exerts an important impact on the mode and efficiency of microwave heating, while the complex dielectric constant (dielectric constant and dielectric loss) of the material is the decisive factor in determining the wave transmission performance of the material. In this work, we measured the complex dielectric constant of polycrystalline mullite fiber board (PMF) in the temperature range of 25–1000 °C, and the effect of temperature on dielectric constant and dielectric loss was analyzed; The wave-transmission properties of the material were calculated according to the theory of electromagnetic wave transmission line, and the effects of temperature, material thickness, polarization modes of electromagnetic wave and incident angle on the wave transmission performance were analyzed. The results reveal that the dielectric constant of PMF does not change much with the increase of temperature, which is about 1.6; The dielectric loss does not change much within 200 °C, but when the temperature is higher than 200 °C, the change presents approximately exponential increase with the rise of temperature. The wave transmission performance fluctuates with the increase of the thickness, and there are maximum value and minimum value, and the overall wave transmission performance decreases with the increase of the material thickness. In a transverse electric (TE) field, the overall wave transmission performance decreases with the increase of the incident angle, and better wave transmission performance can be obtained by priority selection of vertical incidence of electromagnetic wave. In a transverse magnetic (TM) field, with the increase in the incident angle, the wave transmission performance firstly climbs up then declines, and there is an optimal incident angle where total transmission can occur. Finally, this work selected the thickness corresponding to different temperature as the preferred thickness. This work is of important theoretical significance for understanding the mechanism of the dynamic change of the wave transmission performance of the thermal insulation materials in microwave heating, and provides important practical guidance for the design and optimization of microwave heating equipment.

The absorbing performance of pharmaceutical powders has an important effect on the efficiency of microwave drying. In this study, in order to achieve optimal microwave absorption, the reflection lo...

Refractory materials are an important part of industrial microwave heating equipment, and their transmission performance has a significant influence on the efficiency and uniformity of microwave heating. In this study, electromagnetic wave power transmission coefficients (PTCs) of alumina refractory ceramics are calculated within the temperature range of 22–1379 °C and the thickness range of 0–0.1 m at 2.45 GHz, and the influences of the complex dielectric constant of the material, the thickness of the medium, the polarisation mode of the electromagnetic waves, and the incident angle of the electromagnetic waves on PTC are analysed. It was found that the transmission performance of alumina ceramics fluctuates with increasing thickness at different temperatures and that there are several transmission peaks. The transmission performance in a transverse electric (TE) field decreases monotonically with increasing incident angle, and the PTC is equal to zero when the incident angle is 90°. The transmission performance in a transverse magnetic (TM) field increases first and then decreases with increasing incident angle, and there is a transmission peak. Transmission peaks at different thicknesses form a ‘ridge’ at the Brewster's angle, at which the fluctuation amplitude of PTC becomes very small. As the temperature increases, the ‘ridge’ becomes steeper. Finally, the incident angle range with good transmission performance of alumina ceramics in the temperature range of 22–1379 °C is obtained, and the optimal thickness interval at the optimum incident angle (73.8°) is calculated for reference. This research has important guiding significance for the selection and optimisation of refractory ceramic materials for use in microwave high-temperature heating.

Compared with traditional heating methods, microwave heating is widely used in many industrial heating fields because of its advantages, such as material-selective heating, volumetric heating and high-efficiency heating. However, previous studies have shown that the heating mode depends on the transmission performance of refractory insulation materials. In this study, a commonly used refractory material (fused silica ceramics) for microwave heating was studied, according to the law of electromagnetic wave propagation in a single-layer plate, the power transmission coefficient (PTC) of the material at different thickness, temperature and frequency (915 MHz and 2360 MHz) was calculated and analysed, in order to design the refractory structure which has good microwave transmission performance in the whole microwave heating process. The results show that the transmission performance of fused silica ceramics fluctuates regularly with increasing thickness, and there are several microwave transmission peaks in the PTC patterns, the thicknesses corresponding to the transmission peaks at frequency 2360 MHz are in order 0.033 m, 0.065 m and 0.098 m; as the temperature increases, the position of the transmission peaks will shift to a smaller thickness, the transmission performance of fused silica ceramics decreases slightly with increasing temperature. Comparing the transmission performance of mullite, alumina (Al2O3) and fused silica ceramics, it was found that the fused silica ceramics have excellent transmission properties; especially it is at high temperature. The results of this study can provide guidance for the selection of refractory structure materials and sizes as well as the optimization of heating process parameters in high-temperature microwave heating.

In microwave drying technology, research into the dynamic absorbing properties of the powder is indispensable. In this study, the reflection loss coefficient of paracetamol powder under different temperature, water content, and thickness was calculated based on the principle of electromagnetic wave transmission. The results show that the absorption performance of powder fluctuates dynamically with a series of absorption peaks, and the position of the absorption peak shifts toward the smaller thickness direction as the water content increases or the temperature rises. Because of the influence of the powder thickness on absorbing efficiency, the powder thickness should be adjusted in real time to increase drying efficiency. This study provides the thickness range for which the absorption performance of paracetamol powder under different conditions is over 99%. This study is of great significance for understanding the drying mechanism and optimizing process parameters for microwave drying of pharmaceutical powder.

The induced built-in electric field by piezoelectric materials has proven to be one of the most effective strategies for modulating the charge-transfer pathway and inhibiting carrier recombination. In this work, a series of core-shell structured BaTiO3@TiO2 nanowires (BT@TiO2 NWs) heterojunctions were synthesized and the significant coupling effects between BaTiO3 (BT) and TiO2 resulted in surperior piezo-photocatalytic performance, which was demonstrated by three typical types of dyes with high concentrations. The degradation efficiency of 30 mg/L Rhodamine B (RhB), Methylene blue (MB) and Indigo Carmine (IC) solutions by 0.5 g/L BT@TiO2 NWs reached 99.5% in 75 min, 99.8% in 105 min and 99.7% in 45 min, respectively, which are much higher than piezo-photocatalysis systems reported before. To reveal the coupling mechanisms, photoelectrochemical measurements and band diagram analysis were carried out. The carrier concentration was increased from 2.28 × 1017 cm−3 to 4.91 × 1018 cm−3 and the lifetime of charges was improved from 50.37 ms to 60.98 ms due to the construction of a heterojunction between TiO2 and BT. It was proposed that the tilting and bending of the energy band caused by the introduction of a piezoelectric polarization can facilitate carrier separation both in the bulk phase and at the surfaces of semiconductors, resulting in outstanding piezo-photocatalytic properties for highly concentrated dye degradation. This work provides a universal catalyzer for highly concentrated dye degradation.

Flexible piezoelectric energy harvesters have attracted significant attention in recent years due to their ability to convert strain energy associated with bending into electrical energy for low-power wearable electronic devices. Compared with 0–3 type piezoelectric composites, where the piezoelectric phase is isolated within the material, flexible piezoelectric energy harvesters based on a three-dimensional interconnected ceramic skeleton are of particular interest due to their high stress transfer capability and high piezoelectric coefficients. Herein, a three-dimensional interconnected porous barium calcium zirconate titanate (BCZT) pillar-based structure is created via freeze casting, where polydimethylsiloxane (PDMS) is impregnated into the aligned pore channels to form a flexible piezoelectric energy harvester. The effect of porosity on piezoelectric coefficients, ferroelectric properties and energy harvesting performance is investigated in detail. The piezoelectric coefficient and energy harvesting figure of merit are significantly enhanced due to the presence of an aligned pore structure which leads to a high transfer of applied stress into the piezoelectric phase. The highly aligned porosity leads to the creation of a piezoelectric composite with 60 vol% of polymer that exhibits a high output voltage of 30.2 V and current of 13.8 μA. Moreover, the peak power density can reach up to 96.2 μW cm−2, which is significantly higher than that of nanoparticle-based piezoelectric composites. This work demonstrates a promising prospect of utilizing flexible piezoelectric composites for energy harvesting applications.

The coupling between piezoelectricity and photoexcitation has recently been emerged as an effective strategy to improve the catalytic performance of semiconductors. Lead-free Bi0.5Na0.5TiO3 (BNT) is a promising system for effective piezo-photocatalysis owing to its favorable piezoelectricity, photoexcited response, and electrical conductivity. In this work, one-dimensional BNT nanorods prepared by a high-temperature molten-salt method were developed for piezo-photocatalysis applications for the first time, which exhibited excellent catalytic activity. The degradation efficiency of RhB solution (initial concentration C0 = 5 mg/L) in the presence of BNT nanorods reached 95% in 30 min, leading to a high first-order rate constant k of 0.094 min−1. For reveal the underlying mechanisms, the piezoresponse characterization, piezoelectric potential simulation, band diagram analysis, and photoelectrochemical measurements were carried out, and the BNT nanospheres synthesized by hydrothermal method were simultaneously studied for comparison. A higher piezoelectric coefficient d33* of 200 pm/V and a larger potential output under pressure were achieved in the BNT nanorods. The BNT nanorods also displayed the narrower band gap, stronger photocurrent response, and lower charge transfer resistance. These merits enabled the BNT nanorods to exhibit strong piezo-photocatalytic activity. Moreover, it was found that the BNT nanorods showed better piezo-photocatalytic activity for cationic dyes (RhB and MB) than anionic dyes (MO). For RhB, MB, and MO solutions with C0 of 10 mg/L, k values of 0.041, 0.075, and 0.013 min−1 were achieved, respectively.

Refractory materials are extensively applied in microwave heating instruments. Knowledge of the microwave transmission performance of refractory materials is key to improving the heating efficiency of microwave instruments. In this study, the microwave transmission performance of mullite refractory ceramics was systematically investigated with respect to various key factors, including temperature, microwave frequency, material thickness, incident angle, and polarization modes. The results indicated that the microwave transmission performance of mullite ceramics at 915 MHz is generally superior to that at 2450 MHz. As the temperature increases, the microwave transmission performance at both frequencies degrades, and the corresponding high transmissivity (power transmission coefficient > 0.7) zone also decreases. The microwave transmission performance between both polarization modes is significantly different, which is optimal at 0° (vertical incidence) and Brewster's angle, respectively. Moreover, the preferred thickness of mullite ceramics at different frequencies and temperatures was determined. This research provides references for the selection of incident angles and the optimization of material thickness during microwave heating.

As a new kind of solid-state-displaying, upconversion (UC) displaying devices using rare-earth ions as emitters are gaining more and more attentions by pumping with low-cost high-power infra-diode lasers[[1]]. In fact, to practically use the oxides UC phosphors, one of the most important works is the UC luminescence enhancing. On the subject of UC emission enhancement, the present work was spurred by the recent results from our team and Bai et al. that Li doping in Y2O3:Er and Y2O3:Er,Yb can improve the UC luminescence by orders of magnitude[24]. To better understand the enhancing mechanisms, here, we choose Zn as doping agent, which was doped into the Gd2O3 host to observe the UC emissions of Er. The UC luminescence was characterized and possible enhancing mechanisms were verified by the structural analysis.

Conjugation-induced rigidity in twisting molecules provides a new facile but effective avenue toward solution and solid dual-state efficient luminogens. While conjugation rigidifies the molecular conformations in solution, the twisting structure prevents or alleviates detrimental close molecular packing in the solid states, thus synergistically yielding high efficiencies in both solution and solid states.