(Ba0.5Pb0.5)O.La2O3.4TiO2-(Zr0.8Sn0.2)TiO4复合系统的微波介电性能

研究了（Ｂａ０．５Ｐｂ０．５）Ｏ·Ｌａ２Ｏ３·４ＴｉＯ２－（Ｚｒ０．８Ｓｎ０．２）ＴｉＯ４复合系统的微波介电性能、烧结性能和微观结构,发现复合系统由（ＢａＰｂ）６－ｘＬａ８＋２ｘ／３Ｔｉ１８Ｏ５４,Ｌａ４Ｔｉ９Ｏ２４和（Ｚｒ０．８Ｓｎ０．２）ＴｉＯ４３相组成,而（Ｂａ０．５Ｐｂ０．５）Ｏ·Ｌａ２Ｏ３·４ＴｉＯ２除了（ＢａＰｂ）６－ｘＬａ８＋２ｘ／３Ｔｉ１８Ｏ５４和Ｌａ４Ｔｉ９Ｏ２４外还有一未知相,（Ｚｒ０．８Ｓｎ０．２）ＴｉＯ４是单一晶相．复合后,系统的烧结温度比原两系统降低了．复合系统的微波介电常数、频率温度系数、Ｑ因子主要与其中的相组成有关．结果表明未知相很可能具有高介电常数、低频率温度系数、高Ｑ因子．对微波介电性能的测量值和由复合关系导出的计算值进行了比较．     

(Ba0.5Sr0.5)TiO3 modification on etched aluminum foil for electrolytic capacitor

A new method was proposed to form (Ba_0.5Sr_0.5)TiO₃–Al₂O₃ composite oxide film on etched aluminum foils. The specimens were covered with (Ba_0.5Sr_0.5)TiO₃ (BST) layer by dip-coating in citrate solution and subsequent heat-treatment under 400–650 °C, finally by anodizing in a hot boracic acid and borate solution. The BST powders heated under different temperatures were characterized by X-ray diffraction (XRD) and the specific capacitance of the coated specimens heat-treated under different temperatures and times was measured. It is found that the specific capacitance increases initially with enhancing the temperature and reaches to maximum at 550 °C, but slightly decreases with the heat-treatment time. The capacitance was increased by about 35% after BST coating.     

Microstructure and piezoelectric properties of CuO-doped 0.95(K0.5Na0.5)NbO3-0.05Li(Nb0.5Sb0.5)O3 lead-free ceramics

The effects of sintering temperature and the addition of CuO on the microstructure and piezoelectric properties of 0.95(K_0.5Na_0.5)NbO₃-0.05Li(Nb_0.5Sb_0.5)O₃ were investigated. The KNN-5LNS ceramics doped with CuO were well sintered even at 940 °C. A small amount of Cu²⁺ was incorporated into the KNN-5LNS matrix ceramics and XRD patterns suggested that the Cu²⁺ ion could enter the A or B site of the perovskite unit cell and replace the Nb⁵⁺ or Li⁺ simultaneously. The study also showed that the introduction of CuO effectively reduced the sintering temperature and improved the electrical properties of KNN-5LNS. The high piezoelectric properties of d₃₃ = 263 pC/N, k_p = 0.42, Q_m = 143 and tan δ = 0.024 were obtained from the 0.4 mol% CuO doped KNN-5LNS ceramics sintered at 980 °C for 2 h.     

Enhancement in dielectric and ferroelectric properties of lead free Bi0.5(Na0.5K0.5)0.5TiO3 ceramics by Sb-doping

Lead free piezoelectric Bi_0.5(Na_0.5K_0.5)_0.5TiO₃ (pure and 1 wt.%, 2 wt.%, 4 wt.% Sb-doped) ceramics were synthesized away from its MPB. The crystalline nature of the BNKT ceramic was studied by XRD and SEM. Depolarization temperature (T_d) and transition temperature (T_c) were observed through phase transitions in dielectric studies which were found to increase after Sb-doping, thus increasing its usable temperature range. In the study of relaxation behavior, the activation energy for relaxation was found to be 0.33, 0.43, 0.57 and 0.56 eV for pure and Sb-doped samples, respectively. All samples were found to exhibit normal Curie-Weiss law above their T_c. Doping of Sb was found to restrain the diffused character of the pure sample. In P-E loop, Sb-doping was found to increase the ferroelectric properties.Pure and Sb-doped BNKT ceramics exhibited high values of piezoelectric charge coefficient (d₃₃) as 115, 121, 129 and 100 pC/N, respectively.     

Physical properties of new,lead free (Na0.5Bi0.5)(1−x)BaxTi(1−x)(Fe0.5Nb0.5)xO3 ceramics

This study reports on the synthesis of polycrystalline samples of (Na_0.5Bi_0.5)_(1−x)Ba_xTi_(1−x)(Fe_0.5Nb_0.5)_xO₃ with x=0, 0.025, 0.05, 0.075, and 0.1, using the solid-state reaction technique. It investigates the effects of the substitution of sodium and bismuth by barium in the A site and of titanium by iron and niobium in the B site with regard to the free NBT symmetry and dielectric properties were investigated. The crystallographic and dielectric properties were also investigated. The diffractograms showed that all the samples had a single phase character. The increase of ceramic lattice parameters induced an increase in the size of the perovskite lattice. This increase was caused by the increase of the radii of the A and B sites. Room temperature X-ray data revealed that the ceramic structures underwent a gradual distortion with the increase in the composition fraction. Dielectric permittivity was measured in the temperature range of 120–780 K with frequencies ranging from 1 to 10³ KHz. Three anomalies, namely T_d, T₁ and T_m, were detected and noted to coexist at lower T_d and T_m as the rate of substitutions increased. All the samples exhibited a diffuse phase transition and implied better dielectric permittivity maxima values at temperatures approaching room temperature, since the substitution rate values increased more than that of pure NBT. A relaxor behavior with ΔT_m=14 K and ε'_rmax=3876 at 1 kHz was observed for (Na_0.5Bi_0.5)_0.9Ba_0.1Ti_0.9(Fe_0.5Nb_0.5)_0.1O₃ ceramic.     

Size-dependent magnetoelectric response of (Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3)-(Ni0.8Zn0.2)Fe2O4 particulate composites

In this paper, we investigated the effect of magnetic grain size on magnetoelectric responses of particulate magnetoelectric 0.7(Bi_0.5Na_0.5TiO₃-Bi_0.5K_0.5TiO₃)-0.3(Ni_0.8Zn_0.2)Fe₂O₄ (BNKT-NZFO) composites. The coexistence of two chemically separated phases was confirmed using x-ray diffraction analysis. The composites had homogeneous microstructure with controlled grain size. The magnetoelectric response of the BNKT-NZFO composites sensitively depended on the grain size of the NZFO phase and the magnetoelectric voltage coefficients presented a marked enhancement of 33% in the engineered grain size range. This result indicated that tailoring the magnetic grain size physically will provide a powerful mean of enhancing magnetoelectric coupling in a two-phase particulate composite, with large potential application in area of magnetic field sensor.     

Effect of pre-sintering temperature on the structural and dielectric properties of (Ba0.5Sr0.5)TiO3 thin films deposited by sol–gel technique

(Ba_0.5Sr_0.5)TiO₃ thin films have been deposited by sol–gel technique and the effect of pre-sintering temperature on the structural and dielectric properties has been studied. The sol was prepared from barium acetate and strontium acetate powders by dissolving them in acetic acid; while titanium isopropoxide was used as titanium source. Acetyl acetone, 2-methoxyethanol, and formamide were used as chelating agent, diluting reagent, and for getting crack free films, respectively. Two sets of films were prepared; one set pre-sintered at 400 °C while the other one at 600 °C. In all the cases, the final sintering temperature was kept fixed at 700 °C for 2 h. These films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), dielectric constant, and loss measurements and AC conductivity studies. It has been found that with an increase in the pre-sintering temperature from 400 to 600 °C, the dielectric constant increases from 225 to 383 (measured at 100 kHz); whereas, the loss tangent remains nearly constant at 0.03–0.05. The XRD results show better crystallinity and enhanced grain growth in case of films pre-sintered at 600 °C. The FTIR spectra reveals that there is significant removal of organic materials in films with higher pre-sintering temperature as compared to that with lower pre-sintering temperature. The AC conductivity studies show a decrease in the frequency exponent ‘s’ with an increase in the pre-sintering temperature which has been correlated with the reduction in oxygen vacancy densities in the sample with higher pre-sintering temperature.     

Dielectric and impedance spectroscopy of Bi(Ca0.5Ti0.5)O3 ceramic

Bismuth calcium titanate (BiCa_0.5Ti_0.5O₃) ceramic, fabricated by a ceramic processing technique, has been characterized using a variety of experimental techniques. Analysis of basic crystal structure using X-ray diffraction data exhibits the orthorhombic system. Measurements and detailed analysis of some electrical parameters (i.e.,dielectric constant, loss tangent (energy loss), electrical impedance and modulus, conductivity, etc.) of Bi(Ca_0.5Ti_0.5)O₃ in a wide range of frequency (10³–10⁶ Hz) and temperature (30–500 °C) have provided some interesting and useful data and results on structure–properties relationship, conduction mechanism, etc.The role of interface, space charge polarization and Maxwell–Wagner dielectric relaxation in getting high dielectric constant of the material at low frequencies and high temperatures has been discussed. Study of temperature dependence of Nyquist plots clearly shows the contributions of grains in resistive and capacitive properties of the material. The frequency of the applied electric field and temperature strongly affect the dielectric (permittivity and dissipation of energy) and electrical (impedance, electrical modulus and conductivity) characteristics of the material.     

Dielectric and impedance spectroscopy of Sr(Bi0.5Nb0.5)O3 ceramics

A lead free polycrystalline material Sr(Bi_0.5Nb_0.5)O₃ was prepared using a high-temperature solid-state reaction technique. Preliminary X-rays diffraction studies exhibit the formation of a single-phase compound in the orthorhombic crystal system. The study of microstructure of gold-coated pellet by scanning electron microscopy (SEM) shows well-defined and homogeneous distribution of grains on the surface of the sample. Detailed studies of dielectric parameters (i.e., ε_r and tan δ) of the compound as a function of temperature at selected frequencies reveal that the values of these parameters are almost independent of temperature. Studies of impedance and related parameters exhibit that these electrical properties of the material are strongly dependent on temperature, and bear a good correlation with the microstructure of the material. The decrease in value of bulk resistance on increasing temperature suggests the existence of negative temperature co-efficient of resistance (NTCR) in the material. Studies of electric modulus show the presence of hopping conduction mechanism in the material with non-exponential-type of relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius- and NTCR- types of behaviors of the material. The ac conductivity spectrum provides a typical-signature of an ionic conducting system, and is found to obey Jonscher′s universal power law.     

Mechanical characterization of porous Ba0.5Sr0.5Co0.8Fe0.2O3−d

The mechanical stability of porous Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−d (BSCF) material was investigated using depth-sensitive microindentation and ring-on-ring biaxial bending tests. The porous BSCF was characterized as potential substrate material for the deposition of a dense membrane layer. Indentation tests yielded values for hardness and fracture toughness up to a temperature of 400 °C, while bending tests permitted an assessment of elastic modulus and fracture stress up to 800 °C. In addition the fracture toughness was evaluated up to 800 °C measuring in bending tests the fracture stress of pre-indented specimens. The results proof that the indentation-strength method can be applied for the determination of the fracture toughness of this porous material. In comparison to dense material the values of the mechanical parameters were as expected lower but the temperature dependences of elastic modulus, fracture strength and toughness were similar to those reported for dense BSCF.     

Dielectric behaviors of Ba(Mg1/3Nb2/3)O3 modified (Na0.5K0.5)NbO3 ceramics

The effects of Ba(Mg_1/3Nb_2/3)O₃ additives to lead-free (1-x)(Na_0.5K_0.5)NbO₃-xBa(Mg_1/3Nb_2/3)O₃ ceramics have been investigated. XRD patterns, SEM images and Raman spectra have been used to discuss phase structure transitions and microstructure. The dielectric behavior has been also investigated by using the empirical law, the Curie-Weiss law and the spin-glass model. Results show the diffused phase transition behavior to be enhanced by increasing Ba(Mg_1/3Nb_2/3)O₃ addition and the dielectric behavior to be changed to the more short range order of relaxor ferroelectric. Barium and Magnesium cations are suggested to enter into the cation sites and induce the changes of lattice structure, microstructure, compositional fluctuation, cation disorder and correlation of neighboring cluster-sized moments.     

Micro- and macro-indentation behaviour of Ba0.5Sr0.5Co0.8Fe0.2O3−d perovskite

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−d (BSCF) is a candidate material for the application as oxygen separation membrane. However, the requisite mechanical reliability needs to be warranted. Indentation tests on dense BSCF yielded data for hardness, stiffness and fracture toughness up to a temperature of 340 °C. Complementary to this, the fracture toughness was also evaluated up to 800 °C based on an indentation-strength method.Up to 200 °C, the values of all characteristic mechanical parameters decreased. At high temperatures they increased. The morphology of the indentation cracks depended on the applied indentation load. This was taken into account while selecting suitable expressions for calculating indentation toughness. The temperature dependence of the normalised fracture toughness as determined by indentation technique and indentation-strength method matched quite well. They revealed a good agreement with the temperature dependence of previously reported normalised fracture stresses. In addition to this, the effect of annealing on the mechanical properties of the material was also studied.     

Effect of Nb-doping on dielectric, ferroelectric and conduction behaviour of lead free Bi0.5(Na0.5K0.5)0.5TiO3 ceramic

Bi_0.5(Na_0.5K_0.5)_0.5TiO₃ + y wt.% Nb (y = 0-1) piezoelectric ceramics were synthesized by solid state reaction. The effect of varying Nb concentration on various properties of BNKT ceramic has been investigated in detail. The effect of Nb-doping on dielectric and ferroelectric property has been presented. An increase in its depolarization temperature and Curie temperature with Nb concentration was observed. The electrical properties of pure and Nb-doped BNKT ceramic over a wide range of frequencies (20 Hz to 2 MHz) and temperature (30-430 °C) were studied using impedance spectroscopic technique.     

Conventionally Sintered (Na0.5,K0.5)NbO3 with Barium Additions

The effect of Ba additions on sodium potassium niobate (NKN) ceramic bodies was investigated with regard to sintering behavior, densification, and electrical properties. Small additions of Ba retard grain growth and increase density. The approximate solubility limit of Ba is 1.5 mol%. During firing the loss of Na and K was very low. Both electrical phase transitions in NKN are lowered with Ba additions. The Ba-containing bodies show higher permittivity values than hot-pressed materials, while radial coupling and d₃₃ were similar to or higher than those of the conventionally sintered pure materials.     

Mixed reforming of heptane to syngas in the Ba0.5Sr0.5Co0.8Fe0.2O3 membrane reactor

Fuel cells are recognized as the most promising new power generation technology, but hydrogen supply is still a problem. In our previous work, we have developed a LiLaNiO/γ-Al₂O₃ catalyst, which is excellent not only for partial oxidation of hydrocarbons, but also for steam reforming and autothermal reforming. However, the reaction needs pure oxygen or air as oxidant. We have developed a dense oxygen permeable membrane Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃ which has an oxygen permeation flux around 11.5 ml/cm² min at reaction conditions. Therefore, this work is to combine the oxygen permeable membrane with the catalyst LiLaNiO/γ-Al₂O₃ in a membrane reactor for hydrogen production by mixed reforming of heptane. Under optimized reaction conditions, a heptane conversion of 100%, a CO selectivity of 91–93% and a H₂ selectivity of 95–97% have been achieved.     

Phase Transitional Behavior and Piezoelectric Properties of Lead-Free (Na0.5K0.5)NbO3–(Bi0.5K0.5)TiO3 Ceramics

(1− x )(Na_0.5K_0.5)NbO₃–(Bi_0.5K_0.5)TiO₃ solid solution ceramics were successfully fabricated, exhibiting a continuous phase transition with changing x at room temperature from orthorhombic, to tetragonal, to cubic, and finally to tetragonal symmetries. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was found at 2–3 mol% (Bi_0.5K_0.5)TiO₃ (BKT), which brings about enhanced piezoelectric and electromechanical properties of piezoelectric constant d ₃₃=192 pC/N and planar electromechanical coupling coefficient k _p=45%. The MPB composition has a Curie temperature of 370°–380°C, comparable with that of the widely used PZT materials. These results demonstrate that this system is a promising lead-free piezoelectric candidate material.     

Intrinsic Nonstoichiometry in Single-Phase Pb(Zr0.5Ti0.5)O3

Two-phase crucibles made of Pb(Zr,Ti)O₃ with small additions of either PbO or (Zr _x Ti _1-x )O₂, which provide atmospheres of constant PbO activity, permit study of intrinsic nonstoichiometry by thermogravimetry. The width of the single-phase region can be determined by alternate equilibration of a sample with crucible atmospheres of high and low PbO activity. The width of this region for Pb(Zr_0.5Ti_0.5)O₃ is 2.48 mol% PbO at 1100°C.     

Co2O3掺杂对(Na0.8K0.2)0.5Bi0.5TiO3陶瓷结构与电性能的影响

采用传统固相法制备了(Na0.8K0.2)0.5Bi0.5TiO3+xmol%Co3+(BNKT-xCo,x=0-8)无铅压电陶瓷,研究了Co2O3掺杂对BNKT陶瓷的显微结构与电学性能的影响。研究表明:适量的Co2O3掺杂促进了晶粒生长,纯BNKT陶瓷样品在介电温谱上有2个介电反常峰Td和Tm,Co2O3掺杂后使所有陶瓷样品的第一个介电反常峰Td消失,表明Co3+抑制铁电-反铁电相变。室温下样品的介电、铁电和压电性能表明Co2O3起硬性掺杂效应。当x=7时陶瓷样品电性能最佳,其中机械品质因子Qm=498,介电损耗tanδ=2.3%(1kHz),压电常数d33=103pC/N,平面机电耦合系数kp=27%。     

BiScO3 Doped (Na0.5K0.5)NbO3 Lead-Free Piezoelectric Ceramics

Lead-free potassium sodium niobate-based piezoelectric ceramics (1− x )(Na_0.5K_0.5)NbO₃– x BiScO₃ (KNN–BS) ( x =0∼0.05) have been prepared by an ordinary sintering process. Single perovskite phase of KNN–BS exhibits an orthorhombic symmetry at x <0.015 and pseudocubic symmetry at x >0.02, separating by a MPB at 0.015≤ x ≤0.02. Piezoelectric and ferroelectric properties are significantly enhanced in the MPB, which are as follows: piezoelectric constant d ₃₃=203 pC/N, planar coupling coefficient k _p=0.36, remnant polarization P _r=24.4 μC/cm². These solid solution ceramics look promising as a potential lead-free candidate materials.