Low-temperature sintering of Li2O-doped BaTiO3 lead-free piezoelectric ceramics

Low-temperature sintering of BaTiO₃ ceramics using Li₂O as sintering aids was investigated with a special influences of Li₂O content (0–4?mol%) and sintering temperature (1000–1100°C) on crystalline structure and electrical properties. The sinterability of BaTiO₃ ceramics significantly improved by adding Li₂O, whose densification sintering temperature reduced from 1300°C to 1000°C. XRD pattern indicated that BaTiO₃-xLi₂O samples were single phase with a tetragonal symmetry as x?=?0–0.3?mol%, while the samples became an orthorhombic symmetry as x?=?0.5–4?mol%. The densification sintering temperature in which samples showed relative density higher than 90?% decreased with increasing Li₂O content. A maximum d ₃₃ value (200 pC/N) was obtained for the BaTiO₃-0.5?mol%Li₂O sample sintered at 1050°C, which is attributed to a vicinity of the phase transition and the high density. Adding Li₂O not only reduced the sintering temperature but also obtained the acceptable piezoelectric properties, which will make BaTiO₃ become a kind of promising and practical lead-free piezoelectric ceramics.     

High piezoelectric activity in lead-free BaTiO3-BaZrO3-CaTiO3 ceramics with near polymorphic phase boundary

Abstract

Lead-free 0.88BaTiO₃–(0.12-x)BaZrO₃–xCaTiO₃ (BT-BZ-xCT) ceramics were fabricated via solid state reaction. The effect of CaTiO₃ content on crystal structure, phase transition, and electrical properties was investigated systematically. The crystal structure and phase transition of ceramics were characterized by X-ray diffraction (XRD), Raman spectra and dielectric measurement. Results show that ceramic in the composition, x?=?0.02, exhibits a rhombohedral structure. Ceramics with increasing CT content transformed from a rhombohedral to orthorhombic structure in the composition, x?=?0.04, and eventually became a tetragonal structure at the composition, x?≥?0.08. The polymorphic phase boundary (PPB) was observed at the composition, x?=?0.06, with coexistence of orthorhombic and tetragonal phases showing at almost room temperature. This PPB composition exhibited a high piezoelectric response (d₃₃*) of 1,150?pm/V at 10?kV/cm as an electric field was applied. These results indicate that the materials studied have potential as candidates for lead-free piezoelectric ceramics.     

Dielectric and piezoelectric properties of (K0.5Na0.5)(Nb0.97Sb0.03)O3 ceramics doped with Bi2O3

In this study, to develop the optimal composition of ceramics for low loss piezoelectric actuator and ultrasonic motor applications, (K_0.5Na_0.5)(Nb_0.97Sb_0.03)O₃?+?0.009 K_5.4Cu_1.3Ta₁₀O₂₉?+?0.1wt%Li₂CO₃?+?xwt%Bi₂O₃(x?=?0?~?0.9) lead-free piezoelectric ceramics with a fixed quantity of 0.009 K_5.4Cu_1.3Ta₁₀O₂₉ (abbreviated as KCT) were manufactured using the conventional solid-state solution processes. The effects of Bi₂O₃ addition on the dielectric and piezoelectric properties were then investigated. From the X-ray diffraction analysis result the specimens demonstrated orthorhombic symmetry when Bi₂O₃ was less 0.6?wt%, a pseudo-cubic phase appeared when Bi₂O₃ was 0.9?wt%. SEM images indicate that a small amount of Bi₂O₃ addition affect the microstructure. The piezoelectric properties of (K_0.5Na_0.5)(Nb_0.97Sb_0.03)O₃ ceramics were greatly improved by a certain amount of Bi₂O₃ addition. Excellent properties of density?=?4.54?g/cm³, relative densities?=?98.5?%, k _p?=?0.468, Q _m?=?1,715 and d ₃₃?=?183 pC/N were obtained with a composition of 0.3?wt% Bi₂O₃     

Phase formation and dielectric properties of ferroelectric glass-ceramics in Na2O-BaO-Nb2O5-SiO2 system doped with Nd3+

Ferroelectric Glass-ceramics of the Na₂O–BaO–Nb₂O₅–SiO₂ system were obtained from controlled crystallization process performed on the parent glass of composition (24-x)Na₂O-xBaO-26Nb₂O₅-50SiO₂ where x?=?4 was selected. Nd₂O₃ doping was applied in the range 0–3 mol%. X-ray diffraction analysis indicated that NaNbO₃ and NaBa₂Nb₅O₁₅ crystals formed as two main crystalline phases. Their relative intensities varied with treatment temperature. Crystalline sizes of both NaNbO₃ and NaBa₂Nb₅O₁₅ calculated from XRD peak broadening were in nanoscale range. Increasing of doping content also gave a parent glass with higher bulk density. The dielectric constant measured at room temperature for glass-ceramic samples was found to be sensitive to the presence of NaBa₂Nb₅O₁₅ phase. The results of the present work suggest that introduction of Nd³⁺ into Na₂O-BaO-Nb₂O₅-SiO₂ system not only alters the dielectric response but also changes the phase transition behaviors of the co-existant ferroelectric phases by suppressing the growth of the NaBa₂Nb₅O₁₅ crystals.     

Dielectric and piezoelectric properties of La2O3 doped (Bi0.5Na0.5)0.92(Ba0.8Sr0.2)0.08 TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (Bi_0.5Na_0.5)_0.92(Ba_0.8Sr_0.2)_0.08 TiO₃+x mol% La₂O₃(x = 0, 0.1, 0.3, 0.5, 0.8) were synthesized by conventional solid state reaction. The crystal structure of all compositions is mono-perovskite ascertained by XRD. The grain size decreased and diffuse phase transition behavior was more evident with the increasing amount of La₂O₃. The piezoelectric constant d₃₃ and the electromechanical coupling factor k_p showed the maximum value of 165 pC/N and 0.322 at 0.3% and 0.1% La₂O₃ addition, respectively, and rapidly decreased when La₂O₃ addition over 0.5%. The loss tangent tanδ linearly increased and the mechanical quality factor Q_m linearly decreased with the increasing amount of La₂O₃.     

Fabrication of 0.655Pb(Mg1/3Nb2/3)O3-0.345PbTiO3 functionally graded piezoelectric actuator by tape-casting

A 0.655Pb(Mg_1/3Nb_2/3)O₃-0.345PbTiO₃ (PMN-0.345PT) functionally graded (FG) piezoelectric actuator was fabricated by tape-casting. The effects of sintering temperature on the physical and electrical properties of the PMN-PT ceramics were initially investigated. High dielectric and piezoelectric properties of d ₃₃?=?700pC/N, k _p?=?0.61, ??_r?=?4.77?×?103, tan???=?0.014, P _r?=?30.68 ??C/cm² were obtained for the specimens sintered at 1200°C. Compared with the traditional solid-state reaction, the properties of the ceramics were significantly enhanced by tape-casting. The new FG piezoelectric actuator consisted of four layers, and the variation of changes in their d ₃₃ and ?? _r were graded opposite the thickness direction. The relationship between displacement and voltage for the actuator was also determined, with the results showing that it was linear. The driving displacement of the free end of the actuator reached 430.668 ??m.     

High temperature piezoelectric ceramics in the Bi(Mg1/2Ti1/2)O3-BiFeO3-BiScO3-PbTiO3 system

Compositons in the pseudoquaternary system, 1-×(0.35Bi(Mg_1/2Ti_1/2)O₃-0.30BiFeO₃-0.35BiScO₃)—×PbTiO₃ were fabricated and characterised at the morphotropic phase boundary (MPB) between ferroelectric rhombohedral and tetragonal phases. The MPB occurred at ×?≈?0.48 at which composition the ferreoelectric to paraelectric phase transition, T_C?=?450°C, the piezoelectric constant, d₃₃?=?328 pC/N and electromechanical coupling factor, k_p?=?0.44. The piezoelectric properties are viable for actuator applications but lower than equivalent high T_C piezoelectrics such as 0.36BiScO₃–0.64PbTiO₃ (d₃₃?=?450 pC/N, T_C?=?450°C). However, the relative reduction in the Sc₂O₃ content gives a significant cost saving which may prove a commercial advantage.     

Ferroelectric and piezoelectric properties of tungsten doped CaBi4Ti4O15 ceramics

Tungsten doped CaBi₄Ti₄O₁₅ (CBT) ceramics was prepared by solid-state reaction method. A pure single phase of layer-structured ferroelectric with m?=?4 was formed when x?≤?0.025. The effect of W doping on dielectric, ferroelectric and piezoelectric properties was investigated. W⁶⁺ doping increased the temperature stability of dielectric constant and decreased dielectric loss. W⁶⁺ doping decreased the remanent polarization, while the coercive field decreased as well, as a result, the piezoelectric constant was increased. AC conductivity measurement showed that W⁶⁺ doping increased the conductivity of CBT ceramics and showed n-type conducting mechanism. W⁶⁺ doped ceramics has smaller activation energy due to many defects introduced in the crystal lattice.     

Dy2O3掺杂LiDyxMn2-xO4的合成及性能

采用类似溶胶-凝胶法合成稀土金属氧化物Dy2O3掺杂LiDyxMn2-xO4(x=0,0.01,0.02,0.05).通过XRD和恒流充放电测试了稀土金属元素Dy的掺杂对正极材料的结构以及电化学性能的影响.研究结果表明:当掺杂量x=0.02时,材料LiDy0.02Mn1.98O4具有较高的初始比容量(109mAh/g)和循环性能,50次循环后,容量保持率为95%.     

Crystallization behavior and microwave dielectric characteristics of ZnO-(La, Nd)2O3-B2O3-based dielectrics

Crystallizable zinc borate glasses modified with different contents of La₂O₃ or Nd₂O₃ were investigated as a potential low loss dielectric with respect to their crystallization behavior and microwave dielectric characteristics. The glasses were admixed with Al₂O₃ filler and fired at 850°C for 30 min in air to prepare low temperature dielectrics. Crystallization behavior and microwave dielectric properties of the resulting samples strongly depended on the relative content of La₂O₃ or Nd₂O₃ in the glass. As a promising result, the composition of 0.15ZnO-0.25Nd₂O₃-0.6B₂O₃ exhibited k?～?6.5 and Q?～?1194 at the resonant frequency of 18.9 GHz. Near zero temperature coefficient of frequency (TCF) was obtained by additional modification of the composition with ～10 wt.% of TiO₂ filler. Crystallization kinetics of the samples was studied based on the differential thermal analysis (DTA) curves obtained with different heating rates. Correlation of the observed dielectric properties to the crystallization behavior is the main subject of this work.     

High dielectric permittivity of SrBi2Nb2O9(SBN) added Bi2O3 and La2O3

In this paper, the structural and dielectric properties of SrBi₂Nb₂O₉ (SBN) as a function of Bi₂O₃ or La₂O₃ addition level in the radio (RF) and microwave frequencies were investigated. The SBN, were prepared by using a new procedure in the solid-state reaction method with the addition of 3; 5; 10 and 15 wt.% of Bi₂O₃ or La₂O_3. A single orthorhombic phase was formed after calcination at 900 °C for 2 h. The analysis by x-ray diffraction (XRD) using the Rietveld refinement confirmed the formation of single-phase compound with a crystal structure (a?=?5.5129 Å, b?=?5.5183 Å and c?=?25.0819 Å; α?=?β?=?γ?=?90°). Scanning Electron Microscope (SEM) micrograph of the material shows globular morphologies (nearly spherical) of grains throughout the surface of the samples. The Curie temperature found for the undoped sample was about 400 °C, with additions of Bi³⁺, the temperature decreases and with additions of La³⁺ the Curie temperature increased significantly above 450 °C. In the measurements of the dielectric properties of SBN at room temperature, one observe that at 10 MHz the highest values of permittivity was observed for SBN5LaP (5%La₂O₃) with values of 116,71 and the lower loss (0.0057) was obtained for SBN15LaP (15%La₂O₃). In the microwave frequency region, Bi₂O₃ added samples have shown higher dielectric permittivity than La₂O₃ added samples, we highlight the SBN15BiG (15 % Bi₂O₃) with the highest dielectric permittivity of 70.32 (3.4 GHz). The dielectric permittivity values are in the range of 28–71 and dielectric losses are of the order of 10^?2. The samples were investigated for possible applications in RF and microwave components.     

Sintering and dielectric properties of Al2O3 ceramics doped by TiO2 and CuO

The effects of CuO and TiO₂ additives on the microstructure and microwave dielectric properties of Al₂O₃ ceramics were investigated. Al₂O₃ ceramics with CuO and TiO₂ additions can be well sintered to achieve 93∼98% theoretical densities below 1,360 °C due to Ti₄Cu₂O liquid phase sintering effect. The Qf values decreased with increasing CuO and TiO₂ content, due to the formation of the second phase Ti₄Cu₂O. However, the varying behaviors of the dielectric constant (ɛ _r ) and temperature coefficients (τ _f ) were associated with phase constitutions, as a result of the change of CuO and TiO₂content. The τ _f can be shifted close to 0 ppm/°C by controlling the content of CuO and TiO₂. The specimens with 0.5 wt.% CuO and 7 wt.% TiO₂ sintered at 1,360 °C for 4 h showed ɛ _r of 11.8, Qf value of 30,000 GHz, and τ _f of −7 ppm/°C.     

Microwave Sintering of Base-Metal-Electroded BaTiO3 Capacitor Materials Co-Doped with MgO/Y2O3 Additives

In this paper, we systematically investigated the effect of microwave sintering parameters on the characteristics of BaTiO₃ capacitor materials co-doped with Y₂O₃/MgO species. It is observed that the granular structure of the materials is relatively insensitive to the sintering temperature and soaking time such that the BaTiO₃ capacitor materials possessing X7R dielectric constant-temperature (K-T) characteristics can be obtained in a wide range of sintering conditions. TEM examinations reveal that the detailed microstructure of these materials is extremely complicated. The unique K-T properties of these materials are ascribed to the duplex structure of the samples, viz. fine grains of paraelectric phase and large grains of ferroelectric phase.     

La2O3–B2O3–TiO2 Glass/BaO–Nd2O3–TiO2 ceramic for high quality factor low temperature co-fired ceramic dielectric

A conventional BaO–Nd₂O₃–TiO₂ ceramic of microwave dielectric material was added to rare-earth derived borate glasses (La₂O₃–B₂O₃–TiO₂) for use as LTCC (low temperature co-fired ceramic) materials. The sintering behavior, phase evaluation, and microwave dielectric properties were investigated. It was found that increasing the sintering temperature from 750 to 850 °C led to increases in shrinkage and microwave dielectric properties (≈15 for ?_r , >10,000 GHz for Q*f₀ and >94 ppm/ °C for τ _f at 7–8 GHz for resonant frequency). The results suggest that a composite with suitable additives for τ _f could feasibly be developed as a material for LTCC applications.     

Effects of Al2O3 on the piezoelectric properties of Pb(Mn1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

Piezoelectric properties of Al₂O₃-doped Pb(Mn_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ ceramics were investigated. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by X-ray diffractometer for all the specimens doped with Al₂O₃. The highest sintered density of 7.8 g/cm³ was obtained for 0.2 wt% Al₂O₃-doped specimen. Grain size increased by doping Al₂O₃ up to 0.3 wt%, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants increased by doping Al₂O₃ up to 0.2 wt%, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in O^{2 −} ion sites and the substitution of Al³⁺ ions.     

Transport and magnetic properties of Sr doped Nd0.55Ca0.45MnO3

The effect of Sr doping on the transport and magnetism properties of charge/orbital-ordered Nd_0.55Ca_0.45MnO₃ is investigated. A low temperature phase transition from a charge/orbital ordered insulator to a ferromagnetic metal was founded in the Nd_0.55(Ca_1?x Sr _x )_0.45MnO₃ samples. The ground state is the charge/orbital ordered insulator at x?<?0.2, while for x?>?0.3 it changes to a ferromagnetic metal. The resistivities of the samples exhibit almost ideal percolation behavior with a percolation threshold of 0.3. Therefore, this system shows an intricate competition between metallic ferromagnetism and charge/orbital ordered insulator and the percolation behavior demonstrates that the relative volumes of ferromagnetic phase and charge/orbital phases changes with the doping content x and temperature.     

Synthesis and characterization of Eu doped Y2O3 particles by a glycothermal processing

Eu doped Y₂O₃ particles were prepared under high temperature and pressure conditions by precipitation from metal nitrates with aqueous potassium hydroxide. The Eu doped Y₂O₃ particles were obtained at 270°C. The average particle size of synthesized powders was below 1 um. The X-ray diffraction pattern shows that the synthesized particles were crystalline. This study has shown that the synthesis of Eu doped Y₂O₃ crystalline particles is possible under glycothermal conditions in ethylene glycol solution. The effects of synthesis parameters, such as the concentration of starting solution, pH of starting solution, reaction temperature and time, are discussed.     

Nd2O3掺杂对NiZn铁氧体电磁性能的影响

研究了Ｎｉ０．４Ｚｎ０．６ＮｄｘＦｅ２－ｘＯ４铁氧体的电磁性能,从材料的微观结构出发,着重讨论了Ｎｄ＾３＋离子对ＮｉＺｎ铁氧体起始磁导率μ,品质因素Ｑ,截止频率ｆｃ电阻率ρ以及居里温度ＴＣ的影响。     

Microstructure of X7R Type Base-Metal-Electroded BaTiO3 Capacitor Materials Co-Doped with MgO/Y2O3 Additives

Detailed microstructure of MgO/Y₂O₃ co-doped BaTiO₃ materials were examined using transmission electron microscopy (TEM). For the 1250_C-sintered BaTiO₃ samples possessing flat K-T characteristics, which meet the X7R specification, the granular structure is complicated. Most of the grains are very small ( 150 nm) and are highly strained. The small grains contain large proportion of Y₂O₃ species and are paraelectric, whereas the large grains contain Y₂O₃ species unevenly distributed and are of core-shell structure. In contrast, for the 1300C-sintered BaTiO₃ samples, which have K-T properties slightly off the X7R specification, the grains grew larger to around 300 nm. The core-shell structured grains are seldom observed. Apparently, it is the existence of such a non-equilibrium core-shell microstructure, which renders the dielectric properties of the BaTiO₃ materials extremely sensitive to the processing parameters.