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。     

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%.     

Piezoelectric and pyroelectric properties of (Bi0.5Na0.5)0.94Ba0.06TiO3/P(VDF-TrFE) 0–3 composites

Bismuth sodium barium titanate [(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ or BNBT] ceramic powder have been incorporated into a polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE) 70/30 mol%] copolymer matrix to form 0–3 composites. With the composition near the MPB region, BNBT has relatively high piezoelectric and dielectric properties. P(VDF-TrFE) ferroelectric copolymer films can be poled to give piezoelectric and pyroelectric performance without prior mechanical stretching. The composites were prepared using solvent casting to disperse the ceramic powder homogeneously in the copolymer matrix. Composites with BNBT volume fraction ϕ ranging from 0.05 to 0.30 were fabricated using a hot-press method. The piezoelectric and pyroelectric coefficients of the composites were studied as a function of ϕ under different poling conditions. As BNBT has a low relative permittivity, so it is relatively easy to pole the BNBT ceramic inclusion. Hence, the BNBT 0–3 composites were found to have better pyroelectric properties than that of the lead zirconate titante PZT/P(VDF-TrFE) 0–3 composites.     

(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.     

(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.     

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.     

(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。     

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.     

Structure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiCoO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ (x = 0.12–0.24, y = 0–0.04) have been fabricated by a conventional solid-state reaction method, and their structure and electrical properties have been investigated. The XRD analysis shows that samples with y ≤ 0.03 exhibit a pure perovskite phase and very weak impurity reflections can be detected in the sample with y = 0.04. With x increasing from 0.12 to 0.24 and y increasing from 0 to 0.04, the ceramics transform gradually from a rhombohedral phase to a tetragonal phase and rhombohedral–tetragonal phase coexistence to a pseudocubic phase, respectively. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x = 0.18–0.21, y = 0–0.03. The ceramics near the composition of the MPB have good performances with piezoelectric constant d ₃₃ = 156 pC/N and electromechanical coupling factor k _p = 0.34 at x = 0.21 and y = 0.01, which attains a maximum value in this ternary system. Adding content of BiCoO₃ leads to a disappearance of the response in the curves of dielectric constant-temperature to the ferroelectric–antiferroelectric transition. The temperature dependence of dielectric properties suggests that the ceramics are relaxor ferroelectrics. The results show that (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ ceramics are good candidate for use as lead-free ceramics.     

Microwave dielectric properties of (1 − y)Nd(1−2x/3)Bax(Mg0.5Sn0.5)O3–yCa0.8Sr0.2TiO3 ceramic

The (1 ? y)Nd_(1?2x/3)Ba_x(Mg_0.5Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of the Nd_(1?2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ ceramics revealed that Nd_(1?2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ is the main crystalline phase, which is accompanied by a little Nd₂Sn₂O₇ as the second phase. An apparent density of 6.89 g/cm³, a dielectric constant (ε _r ) of 19.1, a quality factor (Q × f) of 212,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?68 ppm/°C were obtained when the Nd_2.94/3Ba_0.03(Mg_0.5Sn_0.5)O₃ ceramics were sintered at 1,550 °C for 4 h. The temperature coefficient of resonant frequency (τ _f ) increased from ?68 to +55 ppm/°C as y increased from 0 to 0.7 when the (1 ? y)Nd_2.94/3Ba_0.03(Mg_0.5Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramics were sintered at 1,600 °C for 4 h. 0.4Nd_2.94/3Ba_0.03(Mg_0.5Sn_0.5)O₃–0.6 Ca_0.8Sr_0.2TiO₃ ceramic that was sintered at 1,600 °C for 4 h had a τ _f of ?7 ppm/°C.     

Structure and electrical properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Bi0.5(Na0.82K0.18)0.5TiO3–BiAlO3 lead free piezoelectric ceramics

0.09(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–(0.01 − x) Bi_0.5(Na_0.82K_0.18)_0.5TiO₃–x BiAlO₃ (BNBKT–xBA) lead-free piezoelectric ceramics were synthesized by conventional solid-state reaction processes. Structure, ferroelectric and piezoelectric properties of BNBKT–xBA ceramics were investigated. X-ray diffraction data shows that BNBKT–xBA ceramics form the pure perovskite phases and the ceramics have the morphotropic phase boundary when x ≤ 0.030. At room temperature, the BNBKT–xBA ceramics at x = 0.030 have better electrical properties, the piezoelectric constant d₃₃ and planar coupling factor k_p of BNBKT–xBA ceramics reaches peak values at x = 0.030: d₃₃ = 217 pC N⁻¹, k_p = 0.308. The remnant polarization P_r, mechanical quality factor Q_m and relative dielectric constant ?_r of BNBKT–xBA ceramics at x = 0.030 attains 33.8 μC cm⁻², 133 and 928 (100 KHz), respectively. As BA content increase, the depolarization temperature T_d shift toward lower temperature, and T_d of BNBKT–xBA ceramics with x = 0.030 decreased to 55 °C.     

Effect of sintering temperature on structure and dielectric behavior of 0.95(Bi0.5Na0.5)0.97(Li0.5Nd0.5)0.03TiO3–0.05BaTiO3 ceramics

Lead free 0.95(Bi_0.5Na_0.5)_0.97(Li_0.5Nd_0.5)_0.03TiO₃–0.05BaTiO₃ (BNTLN0.03–BT5) ceramics were synthesized by conventional solid state reaction route. The effect of sintering temperature (T _s) on structure and dielectric behaviors of BNTLN0.03–BT5 ceramics is investigated systematically. With increasing T _s, the structure of BNTLN0.03–BT5 ceramics transforms from rhombohedral symmetry to pseudo-cubic symmetry. The grain size increases from ~4 to ~10 μm with increasing T _s. The dielectric constants ε _r, dielectric losses tanδ and dielectric frequency dispersion increase gradually at room temperature with increasing T _s. The temperature stability coefficient f _ε of dielectric constant ε _r and the diffuseness coefficient γ increases with increasing T _s. The sharp increase of dielectric constant ε _r in the frequency of 1 kHz above T _m is suppressed with increasing T _s due to reducing Maxwell–Wagner polarization.     

Microstructure and piezoelectric properties of lead-free 0.95(Na0.5K0.5)NbO3–0.05(Bi0.5K0.5)Zr1−x Ti x O3 ceramics

0.95(Na_0.5K_0.5)NbO₃–0.05(Bi_0.5K_0.5)Zr_1?x Ti _x O₃ (abbreviated as KNN–BKZT _x ) ceramics were prepared by the conventional solid state method, and the effect of the Ti content on the surface morphology, crystalline structure, and electrical properties of KNN–BKZT _x ceramics were mainly investigated. With the increase of Ti content, the temperature of the orthorhombic–tetragonal (O–T) phases transitions shifted to lower temperatures, and the O–T phase boundary of KNN–BKZT _x ceramics was identified in the composition with 0 ≤ x ≤ 0.3 at room temperature. It was considered that the piezoelectric properties of the ceramics were enhanced significantly owing to the more possible polarization states resulting from the coexistence of two phases. The ceramic with x = 0.2 exhibited optimum properties: d ₃₃ = 260 pC/N, k _p = 0.38, and T _C = 323 °C.     

Eu0.5Tb0.5(TTA)3Bipy/PMMA的制备及发光性能

合成了一种新型的稀土配合物Eu0.5Tb0.5(TTA)3Bipy,并采用原位乳液聚合法制备了Eu0.5Tb0.5(TTA)3Bipy/PMMA稀土聚合物材料.利用红外光谱仪(IR)、电子探针X射线能谱仪等对稀土聚合物发光材料的结构进行表征,并利用扫描隧道电子显微镜(SEM)、荧光光谱仪(FS)等分别研究了该发光材料的微观形貌,探讨了其发光性能.结果表明,Eu0.5Tb0.5(TTA)3Bipy/PMMA仍保持Eu0.5Tb0.5(TTA)3Bipy原有的发光特性;在365nm紫外光的激发下,产生发光峰在612nm附近、谱线带宽为10.4nm的红光发射,发光亮度高,色纯度高,是性能优良的稀土聚合物发光材料.     

Microstructure,ferroelectric, piezoelectric and ferromagnetic properties of BiFeO3–BaTiO3–Bi(Zn0.5Ti0.5)O3 lead-free multiferroic ceramics

Multiferroic ceramics of (0.70?x)BiFeO₃–0.30BaTiO₃–xBi(Zn_0.5Ti_0.5)O₃ + 1 mol% MnO₂ with perovskite structure were prepared by a conventional ceramic technique and the effects of Bi(Zn_0.5Ti_0.5)O₃ doping and sintering temperature on the microstructure, multiferroic and piezoelectric properties of the ceramics were studied. All the ceramics possess a pure perovskite structure and no second phases can be detected. After the addition of a small amount of Bi(Zn_0.5Ti_0.5)O₃ (x ≤ 0.05), the ferroelectric and piezoelectric properties of the ceramics are improved and the grain growth is promoted. However, excess Bi(Zn_0.5Ti_0.5)O₃ (x ≥ 0.10) retards the grain growth, degrades the ferroelectricity and piezoelectricity, and induces two dielectric anomalies at high temperature. The ceramics can be well sintered at the very wide range of low sintering temperatures (880–980 °C) and exhibit good densification (relative density: 96.2–98.4 %) and strong electric insulation. The increase in the sintering temperature promotes the grain growth and improves the ferroelectricity of the ceramics. The ceramic with x = 0.05 sintered at 880–980 °C possesses improved ferroelectric and piezoelectric properties with remanent polarizations P _r of 21.9–28.1 μm/cm², piezoelectric constants d ₃₃ of 125–139 pC/N and planar electromechanical coupling factors k _p of 30.1–32.4 %, and high Curie temperatures T _C of 523–565 °C. A weak ferromagnetism with remanent magnetizations M _r of 0.0411–0.0422 emu/g and coercive fields H _c of 1.70–1.99 kOe were observed in the ceramics with x = 0–0.025.     

Dielectric and Piezoelectric Properties of (Na0.5Bi0.5)(Ti1–xMnx)O3 (x = 0–0.1) Modified Ceramics

Inorganic Materials - We have studied the crystal structure and dielectric and local piezoelectric properties of (Na0.5Bi0.5)(Ti1–xMnx)O3 (x = 0–0.1) modified sodium bismuth...     

(1-x)CaTiO_3/xNi_(0.5)Zn_(0.5)Fe_2O_4复合材料的制备及其性能

采用固相反应法合成了(1-x)CaTiO3/xNi0.5Zn0.5Fe2O4(0≤x≤1.0)复合材料,并研究了复合材料的物相、微观结构、介电性能和磁性能。结果表明:样品中仅含有钙钛矿型CaTiO3和尖晶石型Ni0.5Zn0.5Fe2O4。1260℃保温3h,样品相对密度达到98.91%,颗粒尺寸约为2μm。样品介电常数随Ni0.5Zn0.5Fe2O4含量(x)增加而增大。当x=0.7、测试频率为103 Hz时,样品介电常数(εr)和介电损耗(tanδ)分别为2629.18和1.74。(1-x)CaTiO3/xNi0.5Zn0.5Fe2O4复合材料显示磁性。其中x=0.7时,样品饱和磁化强度(Ms)达到49.07A·m2/kg;这归因于Ni0.5Zn0.5Fe2O4具有优异的磁性能。     

Zr4+B位置换对(Pb0.5Ca0.5)(Fe(0.5)Nb0.5)O3

研究了Zr4+离子B位置换改性对(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷微波介电性能.实验结果表明,(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3(PCFNZ)陶瓷样品呈现单一斜方钙钛矿相结构.随Zr(4+)离子的置换量增加,PCFNZ陶瓷体系的Qr值和晶粒尺寸逐渐减小;介电常数εr随着置换量增加...