Reduced leakage current and enhanced piezoelectricity of BNT–BT–BMO thin films

BiMeO₃ (where Me denotes a transition metal) is often used as a chemical modifier to form the Bi_0.5Na_0.5TiO₃-based solid solutions and to improve the electromechanical properties of the materials. In this study, BiMnO₃ was selected as a chemical modifier, and (1 − x)(0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃)–xBiMnO₃ thin films with x = 0, 0.005, 0.01, and 0.015 were fabricated using the metal organic decomposition method to study the contributions of the third end-member BiMnO₃ to the reduction in the leakage current and the enhancement of the piezoelectric properties of Bi_0.5Na_0.5TiO₃-BaTiO₃ thin films. Thin films with 1 mol% BiMnO₃ exhibit a lower leakage current, and a better piezoelectricity and ferroelectricity, whose S_max/E_max, P_max, 2E_c, and ε_r are 100.4 pm/V, 48.0 μC/cm², 54.9 kV/cm, and 942, respectively.     

Morphotropic phase boundary in the BNT–BT–BKT system

Lead-free x Bi_0.5Na_0.5TiO₃–y BaTiO₃–z Bi_0.5K_0.5TiO₃ piezoelectric ceramics were synthesized by a conventional solid state reaction method. The microstructure, ferroelectric and piezoelectric properties of the ceramics were investigated. Structure measurements by X-ray diffraction with Rietveld refinement have allowed us to specify more precisely the morphotropic phase boundary (MPB) in this system. For (1 ? x) BNT–x BT solid solution ceramics, the 0.94 BNT–0.06 BT morphotropic composition shows the higher values with d₃₃ = 170 pC/N, k_p = 0.35 and k_t = 0.53. In the case of (1 ? x) BNT–x BKT compositions, the d₃₃, k_p and k_t are, respectively, 137 pC/N, 0.39 and 0.54 for the 0.80 BNT–0.20 BKT ceramic. On the other hand, the ternary 0.865 BNT–0.035 BT–0.100 BKT morphotropic composition shows high piezoelectric constant and electromechanical coupling factors (d₃₃ = 133 pC/N, k_p = 0.26 and k_t = 0.57).     

Phase development and dielectric responses in PMN–BNT ceramics

(1 − x)Pb(Mg_1/3Nb_2/3)O₃–x(Bi_0.5Na_0.5)TiO₃ ceramics were prepared by the conventional mixed-oxide method. All compositions show complete perovskite solid solutions and the structure to change from cubic to rhombohedral at x = 0.5. The dielectric constant and dielectric loss tangent were measured as a function of both temperature and frequency. The results indicated a relaxor ferroelectric behavior for all ceramics. The temperature at maximum of the dielectric constant of PMN–BNT ceramics were seen to increase with increasing BNT content. Moreover, the broadest dielectric peak occurs at x = 0.9, which leads to a morphotropic phase boundary in this system.     

Solid state synthesis and sintering of solid solutions of BNT–xBKT

Various compositions of the solid solution system (100 − x) Bi_0,5Na_0,5TiO₃–xBi_0,5K_0,5TiO₃ (x = 0, 10, 25, 50, 75, 90, 100) were prepared by the mixed oxide route. The formation reaction was analyzed by thermogravimetry coupled with mass spectroscopy and differential scanning calorimetry. In situ high temperature X-ray diffraction up to 770 °C indicated emerging and vanishing of phases during the calcination. Intermediate phases such as alkalipolytitanate (Na/K)₂Ti₆O₁₃ and bismuth titanate Bi₂Ti₂O₇ were identified as forming the perovskite phase. The formation reactions were proposed based on the data obtained. Furthermore the microstructure and the dielectric behavior of the sintered samples were observed by scanning electron microscopy, impedance spectrometry and polarization measurements.     

Fabrication and dielectric properties of transparent PZN–BT ceramic

Transparent ceramic of 0.85Pb(Mg_1/3Nb_2/3)O₃–0.15BaTiO₃ has been successfully prepared by a two-stage sintering method using conventional raw materials. The ceramics exhibited an excellent crystallinity, high density and clean grain boundary. The transmittance keeps about4 0% from visible to near infrared regions. The frequency dependence of T_m and relaxor behavior has also been investigated using Vogel–Fulcher model and Power model.     

Relationship Between Structure and Electric Properties of （0.99–x）BNT–xBKT–0.01KNN Near Morphotropic Phase Boundary

研究了三方、四方共存[即准同型相界（morphotropic phase boundary,MPB）]附近（0.99–x）Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–0.01K0.5Na0.5NbO3[（0.99–x）BNT–xBKT–0.01KNN,x=0.16～0.23]无铅压电陶瓷的电学性能与其结构之间的变化关系。X射线衍射分析表明,随着x的增大,陶瓷材料相结构由三方相转变为四方相。当x=0.20时,（111）和（200）面衍射峰均形成劈裂峰,标志着该组分的相结构由三方–四方相共同组成,形成MPB区。样品的介电温谱表明,铁电–反铁电转变温度（Td）随着x的增大而减小,但Curie点（TC）并未明显变化。电致应变（S）随着x的增大,呈现先增加后减小的趋势,并在x=0.20时得最大值0.46%,此时动态压电系数约为575 pm/V。电滞回线显示,陶瓷样品的剩余极化强度Pr和矫顽场Ec都随着x的增大而减小,分别由41.5μC/cm2降为15.2μC/cm2和由46.5kV/cm降为15.0kV/cm,并伴随着电滞回线由扁平到束腰的形状变化,呈现从铁电相特性到反铁电相特性的转变过程。     

Synthesis,dielectric and relaxation behavior of lead free NBT–BT ceramics

The 0.94(Na_0.5Bi_0.5TiO₃)–0.06BaTiO₃ ceramics have been prepared by the conventional solid state reaction method. Structural analysis of the prepared ceramic was made by means of room temperature XRD, FT-IR and Raman spectra. The formation of perovskite structure is confirmed by XRD and Raman studies. The dependence of dielectric constant on temperature for various frequencies (100 Hz–1.2 MHz) has been determined. The diffuse transition is observed in the variation of dielectric constant and it provides evidence for the relaxor characteristics. The relaxation mechanism of the prepared ceramic is also discussed in detail by using Debye, V–F and Power law relations and the suitable model was predicted by means of goodness of parameter. This is the first time the relaxation process is discussed for the lead free system to the best of our knowledge. High piezoelectric properties with d₃₃=206 pC/N are observed in the present system.     

准同型相界附近(0.99-x)BNT–xBKT–0.01KNN结构与电性能关系

研究了三方、四方共存[即准同型相界(morphotropic phase boundary,MPB)]附近(0.99–x)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–0.01K0.5Na0.5NbO3[(0.99–x)BNT–xBKT–0.01KNN,x=0.16～0.23]无铅压电陶瓷的电学性能与其结构之间的变化关系。X射线衍射分析表明,随着x的增大,陶瓷材料相结构由三方相转变为四方相。当x=0.20时,(111)和(200)面衍射峰均形成劈裂峰,标志着该组分的相结构由三方–四方相共同组成,形成MPB区。样品的介电温谱表明,铁电–反铁电转变温度(Td)随着x的增大而减小,但Curie点(TC)并未明显变化。电致应变(S)随着x的增大,呈现先增加后减小的趋势,并在x=0.20时得最大值0.46%,此时动态压电系数约为575pm/V。电滞回线显示,陶瓷样品的剩余极化强度Pr和矫顽场Ec都随着x的增大而减小,分别由41.5μC/cm2降为15.2μC/cm2和由46.5kV/cm降为15.0kV/cm,并伴随着电滞回线由扁平到束腰的形状变化,呈现从铁电相特性到反铁电相特性的转变过程。     

Remarkably enhanced dielectric stability and energy storage properties in BNT–BST relaxor ceramics by A-site defect engineering for pulsed power applications

Lead-free bulk ceramics for advanced pulsed power capacitors show relatively low recoverable energy storage density(Wrec)especially at low electric field condition.To address this challenge,we propose an A-site defect engineering to optimize the electric polarization behavior by disrupting the orderly arrangement of A-site ions,in which Ba_0.105Na_0.325Sr_0.245−1.5x□_0.5xBi_0.325+xTiO₃(BNS_0.245−1.5x□_0.5xB_0.325+xT,x=0,0.02,0.04,0.06,and 0.08)lead-free ceramics are selected as the representative.The BNS_0.245−1.5x□_0.5xB_0.325+xT ceramics are prepared by using pressureless solid-state sintering and achieve large W_rec(1.8 J/cm³)at a low electric field(@110 kV/cm)when x=0.06.The value of 1.8 J/cm3 is super high as compared to all other W_rec in lead-free bulk ceramics under a relatively low electric field(<160 kV/cm).Furthermore,a high dielectric constant of 2930 within 15%fluctuation in a wide temperature range of 40–350℃is also obtained in BNS_0.245−1.5x□_0.5xB_0.325+xT(x=0.06)ceramics.The excellent performances can be attributed to the A-site defect engineering,which can reduce remnant polarization(P_r)and improve the thermal evolution of polar nanoregions(PNRs).This work confirms that the BNS_0.245−1.5x□_0.5xB_0.325+xT(x=0.06)ceramics are desirable for advanced pulsed power capacitors,and will push the development of a series of Bi0.5Na0.5TiO3(BNT)-based ceramics with high W_rec and high-temperature stability.     

BNT系列原油破乳剂的研究

本文介绍了用KOH作催化剂、伯胺为起始剂、环氧丙烷和环氧乙烷为单体,合成了嵌段数和聚合度不等的14种嵌段聚醚型破乳剂,用瓶试法对陕北油田有代表性的河庄坪、子长原油进行脱水性能测试,发现BNT46对河庄坪原油脱水性能较好。BNT43对子长原油破乳脱水性能较好。     

Characterisation and modelling of CNT–epoxy and CNT–fibre–epoxy composites

Abstract

This research presents an experimental and theoretical investigation on the effects of carbon nanotube (CNT) integration within neat epoxy resin (nanocomposites) and a carbon fabric–epoxy composite (multiscale composites). An approach is presented for the prediction of mechanical properties of multiscale composites. This approach combines woven fibre micromechanics (MESOTEX) with the Mori-Tanaka model which was used for the prediction of mechanical properties of nanocomposites in this research. Nanocomposite and multiscale composite samples were manufactured using cast moulding, resin infusion, and hand lay-up process. The CNT concentrations in the composite samples were from 0 to 5 wt-%. The samples were characterised using tensile, shear and flexural tests. The discrepancy between the theoretical predictions and the experimental observations was hypothesised to be due to dispersion and bonding issues and SEM images are presented in support of the hypothesis.     

BNT系无铅压电陶瓷的研究进展

(Bi1/2Na1/2)TiO3基无铅压电陶瓷是目前研究最广泛,最具吸引力的无铅压电陶瓷体系.本文主要综述了近几年国内外专家重点研究的以BNT为基的4类无铅压电陶瓷,并指出目前国内外学者对钛酸铋钠粉体合成的关注.     

The preparation and properties of zirconia-doped Y–Si–Al–O–N oxynitride glasses and glass-ceramics

Two series (N-9 and N-18 series) of zirconia-doped Y–Si–Al–O–N oxynitride glasses and glass-ceramics were designed. Nominal compositions of the glass samples in equivalent percent (eq%) are xZr: (24–0.25x)Y: (15–0.25x)Al: (61–0.5x)Si: 91O: 9 N and xZr: (24–0.25x)Y: (15–0.25x)Al: (61–0.5x)Si: 82O: 18 N (x=0, 2, 4, 6), respectively. The obtained samples were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Densities, Vickers hardness, fracture toughness, glass transition temperature, and thermal expansion coefficient data were established for each sample. Effect of Zr and N content on glass network structure, thermal and mechanical properties was investigated. It was found that the addition of zirconia is effective in preparing Y–Si–Al–O–N oxynitride glasses with lower glass transition temperature and higher hardness.     

Colloidal Stability and Sintering of Yttria–Silica and Yttria–Silica–Alumina aqueous suspensions

The aim of this work was to produce dense yttrium silicate materials by slip casting, with more than 90% of Y₂SiO₅ phase. The rheological behaviour of concentrated aqueous slips was studied considering the effect of the dispersing additives, solids content and pH. The densification kinetics was examined as a function of temperature and time, and the reactions were analysed in the light of the equilibrium phase diagrams. Deflocculation of the slips was achieved by either an electrostatic mechanism using tetraethylammonium hydroxide, thus requiring a high concentration of base, and by a polyelectrolyte through an electrosteric mechanism, which provided more reliable results. In the binary system Y₂O₃–SiO₂, a very low grade of sintering was obtained at 1600°C. The use of alumina allows sintering through a liquid phase, reaching 90% theoretical density.     

Unique and contrasting mixed-metal lithium–calcium and lithium–barium hexamethyldisilazide complexes

Addition of lithium hexamethyldisilazide to calcium or barium bis(hexamethyldisilazide) in THF resulted in the synthesis of two unique but very different mixed-metal complexes: X-ray crystallography shows these to be, respectively, the heterobimetallic complex [Ca{N(SiMe₃)₂}₃Li(THF)] (1), containing two calcium–lithium bridging amide ligands and the remarkable co-crystalline compound [Ba{N(SiMe₃)₂}₂(THF)₃][Li₂{N(SiMe₃)₂}₂(THF)₂] (2).     

Synthesis and Characterization of Linear and Tri-Block PLLA–PEG–PLLA Blends

This study was conducted to synthesize poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) triblock copolymer (PEGLA) with different poly(L-lactide) block length, and explore its applicability in a blend with linear poly(L-lactide) (3051D NatureWorks) with the intention of improving heat seal and adhesion properties at extrusion coating on paperboard. Poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) was obtained by ring opening polymerization of L-lactide using poly(ethylene glycol) (molecular weight 6000 g mol^?1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy. The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology and differential scanning calorimeter. All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat poly(L-lactide), while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan δ). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.     

Synthesis and Structural Analysis of Co–Zn–Cd Ferrite by Williamson–Hall and Size–Strain Plot Methods

The work aimed at studying the structural properties of Cd-doped cobalt zinc ferrite (Co_0.5Zn_0.5Cd_0.2Fe_1.8O₄) prepared by simple, low-cost solid-state reaction method and characterized by XRD techniques. The X-ray analysis confirms the formation of ferrite particles with a cubic spinel structure. Crystallite size D, lattice constant a, micro strain ε, X-ray density Δ_X, dislocation density ρ _D , hopping lengths (L_A and L_B), bond lengths (A–O and B–O), ionic radii (r_A and r_B), texture coefficients [TC(hkl)], and mechanical properties are also reported.     

Enhanced electrical properties in lead-free NBT–BT ceramics by series ST substitution

Comprehensive electrical properties of 0.94(Na_1/2Bi_1/2)TiO₃–0.06BaTiO₃ lead-free ceramics by doping series SrTiO₃ were investigated. High piezoelectric constant of 205 pC/N and electromechanical coupling factor of 0.34 were obtained due to the forming of the rhombohedral–tetragonal morphotropic phase boundary at x=0.02–0.06. Very large recoverable strain of 0.34% was obtained at x=0.10 due to the coexistence of ferroelectric and relaxor pseudocubic phases. A large electrocaloric effect (ΔT_max=1.71 K and ΔT/ΔE=0.34 K mm kV⁻¹ at 50 kV cm⁻¹) which determined by indirect measurements method was obtained at 120 °C at x=0.02, which is significantly higher than that of lead-free ferroelectric ceramics reported so far. Moreover, lower operating temperatures of 50 °C and 30 °C were proposed when x=0.10 and 0.20 with ΔT_max=0.79 K and 0.6 K, respectively. These properties added together indicate a promising material for applications in cooling systems and actuators.     

Electrocaloric and pyroelectric properties of PZT and PMN–PNN–PZT thin films

The electrocaloric effects (EC) of PZT and PMN–PNN–PZT films were evaluated. PZT and PMN–PNN–PZT thin films with a thickness of 500 nm were fabricated by state-of-the-art chemical solution deposition from a precursor solution with PZT and (PMN?PNN)/PZT=30/70. The polarization hysteresis loop was found to be slim and nonlinear, with smaller hysteretic behavior compared with PZT. The pyroelectric properties evaluated from polarization change and current measurement show that the properties of PMN–PNN–PZT films are superior to those of non-doped PZT films. The electrocaloric temperature changes ΔT due to applied ΔE were calculated. PZT and PMN–PNN–PZT films exhibited ΔT of 2.1 K and 3.6 K at 237.5 °C under a field of 500 kV/cm, respectively. Thermal-electrical energy converters based on pyroelectric effects were investigated for energy harvesting and possible use in ultralow-power sensor modules. The possibilities of pyroelectric energy harvesting using these PZT films were also investigated.