Dielectric properties of Pb[(1?x)(Zr1/2Ti1/2)?x(Zn1/3Ta2/3)]O3 ceramics prepared by columbite and wolframite methods

Polycrystalline samples of Pb[(1 − x)(Zr_1/2Ti_1/2) − x(Zn_1/3Ta_2/3)]O ₃ , where x = 0.1–0.5 were prepared by the columbite and wolframite methods. The crystal structure, microstructure, and dielectric properties of the sintered ceramics were investigated as a function of composition via X-ray diffraction (XRD), scanning electron microscopy (SEM), and dielectric spectroscopy. The results indicated that the presence of Pb(Zn_1/3Ta_2/3)O₃ (PZnTa) in the solid solution decreased the structural stability of overall perovskite phase. A transition from tetragonal to pseudo-cubic symmetry was observed as the PZnTa content increased and a co-existence of tetragonal and pseudo-cubic phases was observed at a composition close to x = 0.1. Examination of the dielectric spectra indicated that PZT–PZnTa exhibited an extremely high relative permittivity at the MPB composition. The permittivity showed a ferroelectric to paraelectric phase transition at 330 °C with a maximum value of 19,600 at 100 Hz at the MPB composition.     

Synthesis of potassium niobate (KNbO3) nano-powder by a modified solid-state reaction

Crystalline lead-free piezoelectric potassium niobate (KNbO₃) powders have been synthesized through a modified solid-state reaction method. The thermal behavior of the K₂C₂O₄·H₂O and Nb₂O₅ raw material mixture was investigated by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The X-ray diffraction technique (XRD) was used to investigate the phase formation and purity. The morphology of the powder obtained was characterized using a scanning electron microscope (SEM). The XRD pattern showed that the monophasic perovskite phase of KNbO₃ could be synthesized successfully at a temperature as low as 550 °C for 240 min, with an average crystallite size of 36 ± 8 nm. The SEM images suggested that the average particle size of the powder obtained was 278 ± 75 nm.     

The modification of surface,size and shape of barium zirconate powder via salt flux

The “top-down” process via direct conversion of the micro (μm)-to-submicroscale (sub-μm) particle was applied in this work by using eutectic chloride salts to prepare BaZrO₃. The particle size at optimum condition could be decreased by more than 10 times from 2.1 ± 0.9 μm to 168 ± 23 nm without destroying the 1:1 of Ba:Zr stoichiometry. The uniform sub-μm-BaZrO₃ powder was sintered in order to obtain ~98% dense ceramic at 1400°C/10 h, which is significantly lower than the 1650°C in normal cases. The microwave dielectric constant, tan δ, and quality factor were also determined. Furthermore, this method also was applied to lead-free piezoelectric material in the 0.87BaTiO₃–0.13BaZrO₃–CaTiO₃ (0.87BT–0.13BZ–CT) system. The particle size of 0.87BT–0.13BZ–CT was reduced greatly from >10 µm to 2.8 ± 0.4 µm. It can be proved that salt flux dissolution method enables high-purity with uniform sub-micro/nanometer powder production in one step by using simple laboratory equipment and low-cost raw materials.     

Highly Flexible Tribovoltaic Nanogenerator Based-on P-N Junction Interface: Comparative Study on Output Dependency Dominated by Photovoltaic Effect in Freestanding-Mode

The emergence of tribovoltaic nanogenerators (TVNGs) paves the way for developing a new kind of semiconductor-based energy harvester that overcomes the restriction of low output current in a conventional approach. The traditional TVNG generally depends on the frictional pair between two rigid semiconductors (or metal-semiconductor), limiting the practicability of flexible and portable electronics. Recent developments require the fundamental understanding of charge generation in diverse operating modes and structures. Here, a flexible TVNG based on the p-Cu₂O/n-g-C₃N₄ interface is presented. Operating in a freestanding mode, the proposed TVNG can generate a stable signal in any optical conditions including UV illumination, dark, and ambient. Under UV illumination, the electrical outputs of the TVNG reach 0.43 V and 2.1 µA cm⁻², which are significantly larger than those obtained from dark and ambient conditions. The results demonstrate the coupling effect of three phenomena: tribovoltaic, photovoltaic, and triboelectric effects, and the unique mechanism to the observed signal is proposed. Additionally, the TVNG shows the practical feasibility of energy harvesting with capacitor charging and charge-boosting circuits. This study showcases the unique concept with potential for developing a novel flexible nanogenerator in many aspects, including material, structure, and fundamental mechanism.     

Solid-state reaction synthesis of sodium niobate (NaNbO<Subscript>3</Subscript>) powder at low temperature

A modified solid-state reaction was applied to produce lead-free piezoelectric sodium niobate (NaNbO₃) powders. The mixture of Na₂C₂O₄ and Nb₂O₅ was identified by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The powders were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The SEM image suggested that the particle size of the powders obtained ranged from 180 to 360 nm. The XRD pattern showed that the pure perovskite phase of NaNbO₃ could be synthesized at the low temperature of 475 °C for 1 h, with an average crystallite size of 31.45 ± 5.28 nm. This temperature was about 300 °C lower than that when using the conventional solid-state method with Na₂CO₃ as reactant, which resulted in a cost-, energy-, and time-saving method.     

Synthesis and ferromagnetic property of new binary copper iron pyrophosphate CuFeP2O7

The pyrophosphate of CuFeP₂O₇ was synthesized through one step-thermal synthesis at 500 °C using the mixing of copper carbonate, iron metals and phosphoric acid. FTIR and XRD results indicate the dominant feature of pyrophosphate (P₂O₇⁴⁻) anion and a pure monoclinic phase with space group C_2h⁶ (Z = 4), respectively. The crystallite size of 25 ± 9 nm for the CuFeP₂O₇ was estimated by X-ray line broadening. Room temperature magnetization result shows ferromagnetic behavior of the CuFeP₂O₇ powder, having hysteresis loop in the range of ± 10,000 Oe with the specific magnetization value of 1.57 emu g^− 1. This property is important for specific application and is presented for the first time.     

Low temperature fabrication of lead-free KNN-LS-BS ceramics via the combustion method

Lead-free piezoelectric 0.992(0.95K_0.5Na_0.5NbO₃–0.05LiSbO₃)–0.008BiScO₃; KNN-LS-BS ceramics were successfully prepared using the combustion method. The highest % perovskite phase was found in the sample calcined at 700 °C for 1 h. The structural phase of orthorhombic structure was also detected in this sample. For the sintered ceramics, a pure tetragonal perovskite phase was observed in the samples sintered between 1025 and 1100 °C. The microstructure of ceramics showed a square or rectangular shape and the average grain size increased with increasing of sintering temperature. The density of the ceramics increased with increasing of sintered temperature up to 1075 °C, were it reached 97.5% of theoretical density and then dropped in value when the sintered temperature further increased. The excellent electrical properties of ε_r at T_c=6600, tanδ at T_c=0.04, P_r (at 40 kV/cm)=19.4 μC/cm² and E_c (at 40 kV/cm)=24.1 kV/cm were obtained in the most dense ceramic. The results indicate that the KNN-LS-BS ceramics are promising lead-free piezoelectric materials.     

CaTiO3 induced ferroelectric phase coexistence and low temperature dielectric relaxation in BaTiO3–BaZrO3 ceramics

The series of 0.86BaTiO₃–(0.14?x)BaZrO₃–xCaTiO₃ (abbreviated as BT–BZ–xCT) ceramics with 0.03 ≤ x ≤ 0.11 were studied to obtain high piezoelectric properties. Rietveld refinement analysis indicated that the BT–BZ–CT compositions follow a gradual rhombohedral (R) → orthorhombic (O) + R → O + tetragonal (T) → T phase transformation with increasing x. Clear evidence of the series of ferroelectric phase transitions was also found in the dielectric results. The R‐O and O‐T transition temperature shifted close to ambient temperature, while the Curie temperature slightly increased with increasing x. In addition to the dielectric loss peaks associated with the structural phase transitions, a broad low‐temperature dielectric loss peak was detected in the R phase at T = 90‐150 K. This dielectric relaxation was attributed to the domain wall freezing and fits well to the Vogel‐Fulcher model with activation energy E_a ≈ 60‐300 meV and freezing temperature T_VF ≈ 75‐140 K. High piezoelectric strain coefficient (d₃₃*) of about 1030 pm/V at 10 kV was achieved at x = 0.07, and a high Curie temperature (T_C) was maintained at about 375 K.     

Floral-like microarchitectures of cobalt iron cyclotetraphosphate obtained by solid state synthesis

Floral-like microparticle of a binary cobalt iron cyclotetraphosphate CoFeP₄O₁₂ was synthesized through solid phase reaction using cobalt carbonate, iron metal and phosphoric acid with further calcinations at the temperature of 500 °C. The XRD and FTIR results indicate that the prepared CoFeP₄O₁₂ has a pure monoclinic phase without the presence of any phase impurities. The floral-like microparticle and superparamagnetic behavior of the synthesized CoFeP₄O₁₂ are important properties for specific applications, which were revealed by SEM and VSM techniques, respectively. The dominant features of the synthesized CoFeP₄O₁₂ in this work are compared with M₂P₄O₁₂ (M = Co and Fe) and CoFeP₄O₁₂ reported in our previous works.