Synthesis and electrical properties of (BaTiO3)1 ?x (K0.5Bi0.5TiO3) x solid solutions

(BaTiO₃)_{1 ? x} (K_0.5Bi_0.5TiO₃) _x solid solutions exhibiting positive temperature coefficient of resistance behavior have been prepared using BaTiO₃ presynthesized through oxalate coprecipitation. The peak in their dielectric permittivity has been shown to shift to higher temperatures (above 120°C) with increasing x. We have examined the effect of K_0.5Bi_0.5TiO₃ content on the microstructure of the (BaTiO₃)_{1 ? x} (K_0.5Bi_0.5TiO₃) _x solid solutions. The results demonstrate that, with increasing x, both the minimum and maximum resistivities of the materials in the temperature range of their positive temperature coefficient of resistance behavior increase. The materials prepared using barium titanate presynthesized by the oxalate route have higher Curie temperatures and temperatures where they exhibit positive temperature coefficient of resistance behavior and lower minimum resistivities than do the materials prepared by solid-state reactions.     

(1 − x)CaTiO3–x(Li0.5Nd0.5)TiO3 for ultra-small dielectrically loaded antennas

Microwave (MW) dielectric ceramics based on the solid solution (1 ? x)CaTiO₃–x(Li_0.5Nd_0.5)TiO₃ (0.25 ≤ x ≤ 1.0) were prepared by conventional solid-state synthesis using the mixed oxide route. Compositions closest to zero τ_f (+65 ppm/°C) were obtained at x = 0.8 where ε_r = 110 and the microwave quality factor, Qf ₀ ? 2600 GHz for samples sintered at 1300 °C. To reduce the sintering temperature and compensate for any Li₂O loss during fabrication, ≤0.5 wt% 0.5Li₂O–0.5B₂O₃ was added as a sintering aid in the form of raw oxides (LBR) and also as a pre-reacted glass (LBG). 0.5 wt% LBR was the most effective, reducing the temperature to achieve optimum density by ~50 °C with no significant deterioration of microwave properties (ε_r = 115, τ_f = +65 ppm/°C and Qf ₀ ? 2500 GHz). The high permittivity and relatively low sintering temperatures (1250 °C) are ideal for the development of low cost ultra-small dielectric loaded antenna, assuming the system can be tuned closer to zero by fractionally increasing x.     

Reaction-sintering of lead-free piezoceramic compositions: (0.95 − x)Na0.5K0.5NbO3–0.05LiTaO3–xLiSbO3

Incorporation of LiSbO₃ into the lead-free piezoceramic composition 0.95Na_0.5K_0.5NbO₃–0.05LiTaO₃ produced a change from an orthorhombic to tetragonal crystal system in samples produced by reaction-sintering. The inferred limit of solid solution along the compositional join, (0.95 − x)Na_0.5K_0.5NbO₃–0.05LiTaO₃–xLiSbO₃, occurred at x ~ 0.06. Differential scanning calorimetry indicated broad peaks at temperatures associated with ferroelectric–paraelectric transitions. The transition temperatures decreased with increasing values of x, up to x = 0.06. Microstructures showed secondary grain growth; a slight decrease in grain-size with increasing LiSbO₃ modification was identified.     

Effects of Co doping on microstructure and properties of (K0.5Na0.5)NbO3–LiSbO3–BiFe(1−x)Co x O3 lead-free piezoelectric ceramics

0.998 [(0.95(K_0.5Na_0.5)NbO₃–0.05LiSbO₃]–0.002BiFe_(1?x)Co _x O₃ (KNN–LS–BF_(1?x)C _x ) lead-free piezoelectric ceramics were prepared by conventional solid-state reaction method. The influences of Co content on the phase structure, microstructure, density and related electrical properties were investigated. The results reveal that the substitution of Co significantly improves the sinterability and the electrical properties of KNN–LS–BF_(1?x)C _x ceramics, sintered at a lower temperature of 1,030 °C, compared with that of KNN–LS–BF ceramics. With increasing x from 0 to 0.8, all samples show a pure perovskite structure, but the grain size increases continuously,and the porosity level reaches it’s lowest value at x = 0.2. The density ρ, piezoelectric constant d ₃₃, coupling factor k _p and dielectric constant ε _r increase with x up to 0.2, and then decrease with further increase in x value, but the variation of dielectric loss tan δ is opposite. The density and electrical properties achieve optimal value of ρ = 4.287 g/cm³, d ₃₃ = 276 pC/N, k _p  = 48 %, ε _r  = 1,284 and tan δ = 1.95 %, when x = 0.2. And Tc ≈ 340 °C at all the variation range of Co content.     

Piezoelectric and dielectric properties of 0.98(Na0.5K0.5)NbO3–0.02Ba(ZrxTi(1−x))O3 ceramics

Lead-free 0.98(Na_0.5K_0.5)NbO₃–0.02Ba(Zr_xTi_(1?x))O₃ (0.98NKN–0.02BZT) ceramics with Zr contents were fabricated by a conventional mixed-oxide method. The results indicate that the Zr/Ti ratio significantly influences the structural, piezoelectric, dielectric, and ferroelectric properties of 0.98NKN–0.02BZT ceramics. For the 0.98NKN–0.02BZT (x = 0) ceramics sintered at 1090 °C, the bulk density increased as the Zr contents decreased and showed a maximum value at x = 0. The Curie temperature of the 0.98NKN–0.02BZT ceramics slightly decreased as the Zr contents increased. The dielectric constant, piezoelectric constant, and electromechanical coupling factor of samples were maximized at x = 0, which might be due to the increase in density. A high d₃₃ = 194 pC/N, k_p = 38% were obtained for the 0.98NKN–0.02BZT ceramics sintered at 1090 °C for 4 h.     

Structures and electrical properties of (Na0.5K0.5)NbO3–Li(Ta0.5Nb0.5)O3 lead-free piezoelectric ceramics

Solid solutions of (Na_0.5K_0.5)NbO₃ (NKN) and Li(Ta_0.5Nb_0.5)O₃ (LTN) were investigated as a potential candidate of lead-free piezoelectric ceramics. It was found that the Curie temperature of solid solutions increases slightly with increasing the LTN content and simultaneously the polymorphic phase transition temperature linearly decrease till below room temperature. An orthorhombic to tetragonal phase transformation at room temperature, or a morphotropic phase boundary, in NKN is induced by ~7 at% LTN addition, where the best dielectric, piezoelectric and electromechanical properties are achieved. The 0.94NKN–0.07LTN ceramics possess a dielectric constant of 765, a loss tangent of 0.04 at 1 kHz, a piezoelectric constant d₃₃ of 253 pC/N and an electromechanical coupling factor k_p of 48%.     

Microstructure and electrical properties of (1 − x)K0.5Na0.5NbO3–x(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 lead-free piezoelectric ceramics

The (1 ? x)K_0.5Na_0.5NbO₃ ? x(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (KNN–BCTZ) lead-free ceramics were fabricated by conventional solid-state sintering technique. The microstructure and electrical properties of the ceramics were investigated. The X-ray diffraction analysis revealed that the ceramics formed a single phase perovskite solid solutions with the symmetry of orthorhombic at x < 0.03. The crystal phase of the ceramics changed from orthorhombic phase to pseudocubic phase when x > 0.04. The coexistence of orthorhombic and pseudocubic (tetragonal) phases was observed near room temperature when 0.03 ≤ x ≤ 0.04. The grains grew up obviously when 2 mol% BCTZ was added, but the grain size was found to reduce gradually with further increasing BCTZ content. The T _C and T _O-T decreased with the increasing BCTZ content. The ferroelectric and piezoelectric properties were abruptly degraded as x ≥ 0.05. Optimum properties (d ₃₃ = 136 pC/N, k _p = 27 %, k _t = 26.5 %, Q _m = 25, P _r = 14.67 μC/cm², E _c = 11.23 kV/cm, T _C = 347 °C, $\varepsilon_{33}^{\text{T}} /\varepsilon_{0} = 8 6 1. 5$ ε 33 T / ε 0 = 8 6 1.5 , tan δ = 0.04) were obtained for the ceramica with x = 0.03.     

Ferroelectric and piezoelectric properties of (1 − x) (Bi0.5Na0.5)TiO3–xBaTiO3 ceramics

Lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT)–barium titanate (BaTiO₃,BT) have been prepared by solid state reaction process. The (1?x)BNT–(x)BT (x = 0.01,0.03,0.05,0.07) ceramics were sintered at 1,150 °C for 4 h in air, show a pure perovskite structure. X-ray diffraction analysis indicates that a solid solution is formed in (1?x)BNT–(x)BT ceramics with presence of a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at x = 0.07. Raman spectroscopy shows the splitting of (TO₃) mode at x = 0.07 confirming the presence of MPB region. The temperature dependence dielectric study shows a diffuse phase transition with gradual decrease in phase transition temperature (T_m). The dielectric constant and diffusivity increases with increase in BT content and is maximum at the MPB region. With the increase in BT content the maximum breakdown field increases, accordingly the coercive field (E_c) and remnant polarization (P_r) increases. The piezoelectric constant of (1 ? x)BNT–(x)BT ceramics increases with increase in BT content and maximum at x = 0.07, which is the MPB region. The BNT–BT system is expected to be a new and promising candidate for lead-free dielectric and piezoelectric material.     

Synthesis and investigation of (1 − x)K0.5Na0.5NbO3–(x)CaSnO3 lead free perovskite ceramics of high dielectric and piezoelectric properties for transducer applications

Journal of Materials Science: Materials in Electronics - The conventional solid state reaction technique was used to synthesize a piezoelectric material of (K0.5Na0.5)NbO3 (KNN) and CS doped KNN...     

(K0.5Na0.5)NbO3–Bi(Mg0.5Ti0.5)O3 solid solution: phase evolution, microstructure and electrical properties

Lead-free piezoelectric ceramics with the composition of (1 ? x)(K_0.5Na_0.5)NbO₃–xBi(Mg_0.5Ti_0.5)O₃ [(1 ? x)KNN–xBMT, 0 ≤ x ≤ 0.04] were synthesized via solid-state reaction method. X-ray diffraction patterns revealed that the orthorhombic—tetragonal phase transition was present for (1 ? x)KNN–xBMT with increasing the content of BMT. The study of dielectric properties illustrated that both peaks of orthorhombic—tetragonal (T _O–T ) and tetragonal—cubic (T _T–C ) phase transitions shifted to lower temperature. Through adding BMT, the electrical properties of KNN ceramics were obviously improved. The optimized piezoelectric and ferroelectric properties with d ₃₃  = 127 pC/N, k _p  = 36.58 %, P _r  = 22.1 μC/cm² were obtained as x = 0.01.     

Sr_(0.5)Ba_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3双层薄膜的微观结构

采用脉冲激光沉积法在(001)LaAlO_3衬底上制备了Sr_(0.5)Ba_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3薄膜,利用透射电子显微镜对薄膜的微观结构进行了研究。结果表明,底电极La_(0.5)Sr_(0.5)CoO_3在LaAlO_3衬底上外延生长并形成立方-立方取向关系。不同于块体结构,LSCO薄膜发生了结构转变,形成一种氧缺位有序调制结构。整个薄膜由大量取向畴组成,其中包含一些层错与反相畴界等缺陷。生长温度为500℃时,Sr_(0.5)Ba_(0.5)TiO_3薄膜为柱状多晶结构;当温度升高至820℃时,薄膜为缺陷较少的单晶结构。     

Effect of Te Substitution on (Tl0.5Pb0.5)Sr2(Ca1?x Te x )Cu2O7 (x=0.0 to 0.5) Superconductor

The (Tl_0.5Pb_0.5)Sr₂(Ca_1?x Te _x )Cu₂O_7??? (Tl-1212) superconductor for x=0.0 to 0.5 has been prepared and studied by a powder X-ray diffraction method, electrical resistance and AC susceptibility measurements. Most of the samples showed Tl-1212 as the major phase and Tl-1201 as the minor phases. Small amounts of Te substitution (x??0.3) maintained the formation of the Tl-1212 phase but larger amounts led to the formation of 1201 and an unknown impurity phase. The resistance versus temperature curve showed metallic behavior for all samples. The resistance versus temperature curves showed onset transition temperature ( $T_{\mathrm{c\ onset}}$ ) between 92 and 97 K. Our results indicated the combined effects of Te substitution, heating temperature and heating time on the formation and optimization of the (Tl_0.5Pb_0.5)Sr₂(Ca_1?x Te _x )Cu₂O₇ superconductor.     

Effect of bond valence on microwave dielectric properties of (1 − x)CaTiO3–x(Li0.5La0.5)TiO3 ceramics

The origins of microwave dielectric properties (1 ? x)CaTiO₃–x(Li_0.5La_0.5)TiO₃ (0.2 ≤ x ≤ 0.8) ceramics, prepared by a conventional solid-state reaction method, were investigated based on the theory of bond valence. The XRD and SEM results showed that complete solid solutions with orthorhombic perovskite structure were formed in the whole investigated compositional range. The dielectric constant (?_r), quality factor (Q × f) and temperature coefficient of resonant frequency (τ_f) were closely related to B-site, A-site and the difference between A-site and B-site bond valences of ABO₃ perovskite compounds, respectively. As x value increased from 0.2 to 0.8, the dielectric constant increased from 198.3 to 276.8, the Q × f value decreased from 4340 to 1880 GHz, and the τ_f value varied from +489.7 to ?178 ppm/°C. For practical applications, excellent microwave dielectric properties of ?_r = 245, Q × f = 2750 GHz and τ_f = +0.75 ppm/°C were obtained for 0.4CaTiO₃–0.6(Li_0.5La_0.5)TiO₃ ceramics.     

Phase transition and piezoelectric properties of (1−x)(K0.42Na0.58)(Nb0.96Sb0.04)O3–x(Bi0.5Na0.5)0.90Mg0.10ZrO3 lead-free ceramics

(1?x)(K_0.42Na_0.58)(Nb_0.96Sb_0.04)O₃–x(Bi_0.5Na_0.5)_0.90Mg_0.10ZrO₃ [(1?x)KNNS–xBNMZ] lead-free ceramics have been prepared by the normal sintering, and effects of BNMZ content on their phase structure, microstructure, and electrical properties have been systematically investigated. These ceramics with 0.045 ≤ x ≤ 0.05 possess a rhombohedral–tetragonal (R–T) phase boundary, as confirmed by the temperature dependence of dielectric properties and X-ray diffraction patterns. The grain size of the ceramics first increases and then decreases as the BNMZ content increases, and the ceramic with x = 0.06 possesses much smaller grains (<1 μm), resulting in the abnormal electrical and phase transition behavior. In addition, the Mg²⁺ was homogenously distributed in the ceramic matrixes. These ceramics with R–T phase boundary show enhanced dielectric, ferroelectric, and piezoelectric properties as compared with a pure KNN, and optimum electrical properties (e.g., P _r ~ 16.23 μC/cm², E _C ~ 7.58 kV/cm, ε _r ~ 2,663, tan δ ~ 0.034, d ₃₃ ~ 434 pC/N, k _p ~ 0.47, and T _C ~ 244 °C) were found in the ceramic with x = 0.0475. We believe that the (1?x)KNNS–xBNMZ ceramic is a promising candidate for lead-free piezoelectric devices.     

(0.84-x)Na_(0.5)Bi_(0.5)TiO_3-0.16K_(0.5)Bi_(0.5)TiO_(3-x)SrTiO_3系无铅压电陶瓷结构与电性能

采用固相法制备了Bi补偿的(0.84-x)Na0.5Bi0.5TiO3-0.16K0.5Bi0.5TiO3-x SrTiO3(简称NBTKBT-xST)无铅压电陶瓷,研究不同ST掺量对体系陶瓷的结构与电性能的影响规律。结果表明,在掺杂范围内(0≤x≤0.06),材料均能形成单一的钙钛矿固溶体结构。随着x的增加,陶瓷晶体结构逐渐由三方相向四方相过渡,且该体系的三方-四方准同型相界(MPB)位于0.03≤x≤0.04。在此组成区域内,体系陶瓷的铁电与压电性能较好,其中x=0.04时,材料的电性能较好:压电常数d33=156 pC/N,平面机电耦合系数k p=0.29,相对介电常数εr=1116,介质损耗tanδ=4.1%,剩余极化强度P r=30.5μC/cm2,矫顽场E c=23.9 kV/cm。介电温谱和变温电滞回线表明体系陶瓷在T d以上可能存在极性相与非极性相共存。     

水热法制备K0.5 Bi0.5 TiO3纳米粉体

以Bi(NO3)3·5H2O、Ti(OC4H9)4、KOH为原料,研究和分析了水热条件下纳米K0.5Bi0.5TiO3(KBT)粉体和影响KBT晶体生长与形成的各个影响因素,并利用XRD、TEM、ED等分析方法对所得粉体的晶相、微观形貌、分散性等性质进行了表征.结果表明,反应温度为180℃,保温时间为24h,KOH浓度为4～12mol/L时能制备出纯净的、结晶完整、分散性良好、钙钛矿型的纳米K0.5Bi0.5TiO3晶体,其颗粒尺寸为15～75nm.