Dielectric and Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3–PbTiO3–Pb(Mg1/2W1/2)O3 Ceramics

Data are presented on the phase composition, crystal structure, microstructure, and dielectric and piezoelectric properties of (1 – y)[(1 – x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃]–yPb(Mg_1/2W_1/2)O₃ (x = 0.30–0.36; y = 0, 0.05, 0.10) ceramics. It is shown that the use of fine-particle magnesia as a starting reagent ensures the formation of single-phase materials. The ceramics with a rhombohedral structure are found to exhibit relaxor behavior. Increasing the content of the Pb(Mg_1/2W_1/2)O₃ perovskite leads to ordering of the domain structure of poled ceramics and increases their piezoelectric charge coefficient d ₃₁ and the width of their phase transitions.     

Low-temperature sintering and piezoelectric properties of Pb(Fe2/3W1/3)O3–added Pb(Zn1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 ceramics

Low-temperature sintering of (a–x)Pb(Zr_0.48Ti_0.52)O₃–bPb(Ni_1/3Nb_2/3) O₃–cPb(Zn_1/3Nb_2/3)O₃–xPb(Fe_2/3W_1/3)O₃ (a + b + c + x = 1, 0.06 ≤ x ≤ 0.10) ceramics were prepared through two-step synthesis process using perovskites-structured ferroelectric materials Pb(Fe_2/3W_1/3)O₃ (PFW) as a sintering aid. The effects of PFW content on the densification, microstructure, phase structure, dielectric and piezoelectric properties of the ceramics were investigated. The sintering temperature was reduced from 1,180 °C (without PFW addition) to 940 °C when the material was PFW-doped. PFW-doping increased the sintered density and the average grain size of PFW–PNN–PZN–lead zirconate titanate ceramics. The ceramics sintered at 940 °C for 4 h with x = 0.08 exhibited favorable properties, which were listed as follows: d₃₃ = 496pC/N, εT 33/ε₀ = 3,119, tanδ = 2.1 % and Curie temperature = 242 °C. These values indicated that the newly developed composition might be suitable for multilayer piezoelectric devices application.     

Enhanced thermal stability and large piezoelectric properties of Sm-doped Pb(Sc1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 multifunctional ceramics

Journal of Materials Science - The crystal structure, electric properties, thermal stability and optical properties of Sm-doped 0.15Pb(Sc1/2Nb1/2)O3–0.50Pb(Mg1/3Nb2/3)O3–0.35PbTiO3...     

Dielectric and electromechanical properties of Mn-doped 0.2875 Pb(Mg1/3Nb2/3)O3–0.2875 Pb(Yb1/2Nb1/2)O3–0.425 PbTiO3 ceramics

In this study, 0.2875 Pb(Mg_1/3Nb_2/3)O₃–0.2875 Pb(Yb_1/2Nb_1/2)O₃–0.425 PbTiO₃ (0.2875PMN–0.2875PYbN–0.425PT) ternary ceramic composition was doped with 1 mol% MnCO₃ in order to induce hard character for potential high-power applications. Dense 0.2875PMN–0.2875PYbN–0.425PT ceramics with 1 mol% MnCO₃ addition were fabricated after sintering at 1100 °C. ε _r = 1728, tanδ = 0.35 %, d ₃₃ = 320 pC/N, d ₃₁ = ?103 pC/N, Q _m = 467, k _p = 0.40, k ₃₁ = 0.24, k ₃₃ = 0.49, and T _c = 280 °C were measured for Mn-doped ceramics. However, undoped ceramics had ε _r = 2380, tanδ = 1.95 %, d ₃₃ = 433 pC/N, d ₃₁ = ?145 pC/N, Q _m = 60, k _p = 0.43, k ₃₁ = 0.27, k ₃₃ = 0.48, and T _c = 285 °C. Acceptor Mn²⁺/Mn³⁺ ions presumably substituted B-site ions in the perovskite structure and formed defect dipole pairs. The electrically “hard” character was induced as a result of the domain wall pinning due to the existing defect pairs. Particularly, increasing Q _m from 60 to 467 and decreasing tanδ from 1.95 to 0.35 % after Mn doping showed that Mn-doped 0.2875PMN–0.2875PYbN–0.425PT ceramics with “hard” character are potential candidates for high-power projector and transducer applications.     

Dielectric relaxation in Ba(Y1/2Nb1/2)O3–BaTiO3 ceramics

Lead-free (1 ? x)Ba(Y_1/2Nb_1/2)O₃–xBaTiO₃; (0 ≤ x ≤ 1) ceramics have been synthesized using solid-state reaction method and characterized by X-ray diffraction, scanning electron microscopy, dielectric and impedance studies. The crystal-structure of the compounds is found to be cubic with the space group Pm3m(221) except for BaTiO₃ for which it is tetragonal (P4/mmm). Complex impedance spectroscopy analysis indicated the presence of non-Debye type dielectric relaxation in Ba(Y_1/2Nb_1/2)O₃–BaTiO₃ system. Compound 0.25Ba(Y_1/2Nb_1/2)O₃–0.75BaTiO₃ exhibited a low value of temperature coefficient of capacitance (<±8 %) in the working temperature range (up to +100 °C), room temperature dielectric constant equal to 295 and low loss tangent (0.039) which meets the specifications for “Z5F” of Class I dielectrics of Electronic Industries Association. Hence, this composition might be a suitable candidate for capacitor applications. Ac conductivity and electric modulus studies supported the hopping type of conduction in the system and frequency dependent ac conductivity data obeyed Jonscher’s power law.     

Enhanced energy-storage properties of SrTiO3 doped (Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3 lead-free antiferroelectric ceramics

The energy-storage properties of SrTiO₃-doped (15, 20, 25, and 30 mol%) 0.80Bi_1/2Na_1/2TiO₃–0.20Bi_1/2K_1/2TiO₃ lead-free antiferroelectric ceramics were investigated by two-step sintering method. The ceramics with higher SrTiO₃ content had smaller grain sizes and a more homogeneous distribution. About 25 mol% SrTiO₃ doping induced antiferroelectric properties, showing a typical double hysteresis loops, accompanied by a large energy density. The first sintering temperature of the ceramics had main impact on the relative density, and the high relative density possessed large external breakdown strength. The optimum electrical performances with a low remanent polarization (P_r = 1.9 μC/cm²), a low coercive field (E_c = 1.7 kV/cm) and a large energy density (W = 0.97 J/cm³) at 10 Hz were obtained at 1,190 °C for a SrTiO₃ content of 25 mol%.     

Ferroelectric properties of (1 − x)Bi(Zn1/2Ti1/2)O3–xPbZrO3 ceramics

The (1 − x)Bi(Zn_1/2Ti_1/2)O₃–xPbZrO₃ solid solution ceramics were prepared by using solid-state reaction method, and their ferroelectric properties were investigated. It was found that the perovskite structure is stable for compositions with x ≥ 0.900. Within this composition range, the crystal structure of the solid solution preserves the orthorhombic symmetry of PbZrO₃ (PZ). The Curie point of the ceramics was found to decrease with increasing Bi(Zn_1/2Ti_1/2)O₃ (BZT) content. The intermediate ferroelectric phase of PZ was stabilized by BZT addition and exists within a much wider temperature range in the solid solution.     

Effect of oxygen vacancies on ferroelectric behavior of Na1/2Bi1/2TiO3–BaTiO3 single crystals

One of the important lead-free ferroelectric solid solutions, sodium bismuth titanate–barium titanate Na_1/2Bi_1/2TiO₃–BaTiO₃ (NBT–BT) was grown by the conventional flux technique. In order to study the role of oxygen vacancies on the dielectric/ferroelectric properties, some of the crystal samples oriented along (0 0 1) and (1 0 0) planes were subjected to oxygen and nitrogen annealing processes to create different concentrations of oxygen vacancies in the samples. Dielectric and its loss measurements were carried out to analyze the role of oxygen vacancies and their corresponding dielectric behavior on NBT–BT crystals. Electron energy loss spectrum (EELS) has revealed that increasing oxygen vacancies has reduced oxidation states of Ti. X-ray rocking curve analysis has confirmed the degradation in the structural quality also on increasing the oxygen vacancies.     

Ferroelectric and piezoelectric properties of high temperature perovskite-type 0.69BiFeO3–0.02Bi(Mg1/2Ti1/2)O3–0.29BaTiO3 ceramics

Lead-free high-temperature piezoceramics of MnO₂-doped 0.69BiFeO₃–0.02Bi(Mg_1/2Ti_1/2)O₃–0.29BaTiO₃ (BF69–BMT2–BT29) were prepared with solid state reaction method. Those ceramics were crystallized in a pure pseudocubic perovskite-structured phase. In contrast to high dielectric loss BF–BT binary solid solution ceramics, low dielectric loss ceramics were obtained here with combined strategies of refined electroceramic processing, Mn-doping and adding BMT third member. Ferroelectric and piezoelectric properties were systematically measured. Here, the 0.30 wt% MnO₂-doped BF69–BMT2–BT29 ceramics sintered at 900 °C for 10 h showed a better combination of ferroelectric and piezoelectric properties than those BiFeO₃–BaTiO₃ piezoceramics.     

Processing and electrical properties of (1 − x)[(1 − y)(Pb(Mg1/3Nb2/3)O3)–y(Pb(Yb1/2Nb1/2)O3)]–xPbTiO3 ceramics

Ferroelectric ceramics in the vicinity of morphotropic phase boundary (MPB) with compositions represented as (1 ? x)[(1 ? y)(Pb(Mg_1/3Nb_2/3)O₃)–y(Pb(Yb_1/2Nb_1/2)O₃)]–xPbTiO₃ were prepared by solid state reaction. The addition of PYbN to PMN–PT decreased the sintering temperature from 1200 °C (y = 0.25) to 1000 °C (y = 0.75). The PT content, where the MPB was observed, increased with the PYbN addition. A remanent polarization value of 28.5 µC/cm² and a coercive field value of 11 kV/cm were measured from 0.62[0.25PMN–0.75PYbN]–0.38PT ceramics, which were close to the ones measured from PMN–0.32PT ceramics. In addition, the Curie temperature was found to increase with PYbN additions.     

Optical properties and structure of R2O–Ga2O3–SiO2 and RO–Ga2O3–SiO2 glasses

Refractive index and molar refraction of Li₂O–, Na₂O–, CaO–, and BaO–Ga₂O₃–SiO₂ glasses have been used to test the validity of a structural model of silicate glasses containing Ga₂O₃ glasses. Ga₂O₃ enters these types of glass in a similar manner as Al₂O₃. It is assumed that, for (SiO₂/Ga₂O₃) >1 and (Ga₂O₃/R₂O) ≤1, Ga₂O₃ associates primarily with modifier oxides to form GaO₄ units. The rest of modifier oxide forms silicate units with non-bridging oxygen ions. Silicate structural units have the same factors as found for binary alkali- and alkaline earth silicate glasses. Differences between experimental and model values suggest another structure for (Ga₂O₃/SiO₂) ≥1.     

Structural and Electrical Properties of Epitaxial La2/3Ca1/3MnO3/La1/3Ca2/3MnO3/YBa2Cu3O7?δ Trilayers

Trilayers made of perovskite-type ferromagnetic?(F), antiferromagnetic?(AF) and superconducting?(S) films were fabricated and their microstructural properties studied. Epitaxially strained La_2/3Ca_1/3MnO₃/La_1/3Ca_2/3MnO₃/YBa₂Cu₃O_7??? (F/AF/S) trilayers were grown in situ by dc-sputtering technique onto (001)-oriented SrTiO₃ (STO) substrates. Whereas the thickness of the bottom?(F) and top?(S) layer was fixed to 74?nm and 100?nm, respectively, that of the intermediate AF layer was varied between ??4?nm and ??9?nm. The crystalline quality of the samples was checked by X-Ray diffraction (XRD) analysis. The ???C2?? scans and reciprocal space maps at (002) and (013) Bragg reflections provided clear evidence for the heteroepitaxial growth of the trilayers as well as for the absence of secondary phases. Due to high epitaxiality of the trilayers, their magnetic response was already shown to develop an excellent magnetic anisotropy to clearly visualize the superconducting diamagnetism and ferromagnetic behavior at a same temperature. The superconducting diamagnetic response at 5?K has now been used to calculate the superconducting current density of the S layer as a function of an applied magnetic field. The results confirmed the uncoupling role of the AF layer. The presence of well defined AF barriers (La_1/3Ca_2/3MnO₃) in the trilayers was also evidenced by recording the I?CV characteristic in cross configuration, which showed an anisotropic behavior as well. The results achieved suggest that such oxide heterostructures could play an important role in the search for novel devices based on magnetic junctions.     

多元复合正极材料LiNi1/3Co1/3Mn1/3O2的研究进展

综述了多元过渡金属Ni、Co、Mn复合正极材料LiNi1/3Co1/3Mn1/3O2的结构、电化学性能、制备方法及LiNi1/3Co1/3Mn1/3O2的改性等研究进展,对其特性进行了总结并展望了多元复合材料的发展方向.     

锂离子电池正极材料LiNi1/3 Co1/3 Mn1/3O2的研究进展

介绍了锂离子电池正极材料LiNi1/3Co1/3Mn1/3O2的结构,综述了LiNi1/3Co1/3Mn1/3O2的正极材料制备与改性及其电化学性能研究,并对其应用前景进行了展望.     

Microwave dielectric properties and applications of Ba(Zn1/3Nb2/3)O3–Ca(Zn1/3Nb2/3)O3 composite ceramics by one-step synthesis method

(1 ? x) Ca(Zn_1/3Nb_2/3) O₃ ? xBa(Zn_1/3Nb_2/3)O₃ (short for CZN/BZN, x = 0–1.0) ceramics were prepared and investigated through the “one-step synthesis method” method. The structure of the system was analyzed using X-ray diffraction. The microstructure of the sintered pellet was analyzed using scanning electron microscopy. Dielectric constant (ε_r), temperature coefficient of resonant frequency (τ_f) and the unloaded quality factor (Q × f) were measured in the microwave frequency region. Two dielectric properties were firstly in the rising tendency and then decreasing with the increased x. On the other hand, a good combination of microwave dielectric properties (ε_r = 24, Q × f = 23,510 GHz τ_f = ?9 ppm/°C) were obtained at x = 0.1. The compositions have excellent microwave dielectric properties and hence are suitable for ceramic capacitors or dielectric resonators applications.     

锂离子电池正极材料LiCo1/3Ni1/3Mn1/3O2的研究进展

综述了近几年锂离子电池正极材料层状三元过渡金属氧化物LiCoxNiyMn1-x-yO2的研究进展，重点讨论了综合性能优异的LiCo1/3Ni1/3Mn1/3O2的电化学性能、结构、制备方法以及存在的不足，LiCo1/3Ni1/3Mn1/3O2与其它商业化正极材料相比具有高容量、热稳定性好、高倍率放电等诸多优异的性能，若能解决循环、存放等问题，将有望成为新一代锂离子电池正极材料。