A 20 MHz single-element ultrasonic probe using 0.91Pb(Zn(1/3 )Nb(2/3))O(3)-0.09PbTiO(3) single crystal

A 20 MHz single-element ultrasonic probe using 0.91Pb(Zn(1/3 )Nb(2/3))O(3)-0.09PbTiO(3) (PZN-PT 91/9) single crystal has been fabricated. The single crystal of PZN-PT 91/9 orientated to the (001) plane has longitudinal coupling factor of k(33)>90%, which is much larger than the k(33)=70 to 80% of conventional Pb(Zr(1-x),Ti(x))O(3) (PZT) based ceramics. A single crystal of PZN-PT 91/9 without inclusion or crack has been grown with dimensions of about 25x15x5 mm by the self-flux method. Because mechanical strength in the fabrication of disk transducers orientated to the (001) plane was sufficiently strong, under the same conditions as are applied to conventional PZT ceramics, a piston single-element probe with a diameter of 2.0 mm and a frequency of 20 MHz was successfully fabricated. The bandwidth of the PZN-PT 91/9 probe was 13-26 MHz, which was 4 MHz broader than that of the conventional PZT probe.     

Relaxor behavior, polarization buildup, and switching in nanostructured 0.92 PbZn1/3Nb2/3O3-0.08 PbTiO3 ceramics

The relaxor-type behavior, electrical polarization buildup, and switching in 0.92Pb(Zn(1/3)Nb(2/3))O(3)-0.08PbTiO(3) nanostructured ceramics with a grain size of approximately 20 nm is reported for the first time. This composition presents the highest-known piezoelectric coefficients, yet phase stability is an issue. Ceramics can only be obtained by the combination of mechanosynthesis and spark-plasma sintering. The results raise the possibility of using nanoscale, perovskite-relaxor-based morphotropic-phase-boundary materials for sensing and actuation in nanoelectromechanical systems.     

Forty-channel phased array ultrasonic probe using 0.91Pb(Zn(1/3 )Nb(2/3))O(3)-0.09PbTiO(3) single crystal

A 0.91Pb(Zn(1/3)Nb(2/3))O(3)-0.09PbTiO (3) (PZN-PT) single crystal with high electromechanical coupling factor (k(33))>90% has been used to fabricate a 40-channel phased array ultrasonic probe with greater sensitivity and broader bandwidth than conventional probes. This probe has a center frequency of 3.5 MHz and an aperture of about 6.0x7.5 mm. The standard probe fabrication process was modified for PZN-PT. The dispersion of echo signals was within +/-20% of the mean value. After recovery poling, the echo amplitude of the PZN-PT single-crystal probe is 8 and 5 dB higher than that of one- and two-matching-layer PZT probes, respectively. Moreover, the fractional bandwidth of the single-matching-layer PZN-PT probe is broader than that of the two-matching-layer PZT probes. The PZN-PT single crystals provide great improvements in the sensitivity and bandwidth of phased array probes.     

(YCa)F3助烧AlN陶瓷的显微结构和热导率

采用（ＣａＹ）Ｆ_３为助烧结剂，低温烧结（１６５０℃， ６ｈ）制备出热导率为２０８Ｗ／ｍ·Ｋ的ＡＩＮ陶瓷，在烧结过程中，热导率随保温时间的变化服从方程：λ（ｔ）＝λ∞－△λ（０）·ｅ~（－ｔ／ｒ）·用ＳＥＭ、 ＳＴｈＭ、 ＴＥＭ和 ＨＲＥＭ对 ＡＩＮ陶瓷的显微结构及其对热导率的影响进行了研究，结果表明，晶粒尺寸对ＡＩＮ陶瓷热导率的影响可以忽略，而分隔在ＡＩＮ晶粒之间的晶界相会降低热导率。     

Crystal structure and microwave dielectric properties of Ba[(Zn1-xMgx)1/3Nb2/3]O3 ceramics

Journal of Materials Science: Materials in Electronics - Ba[(Zn1-xMgx)1/3Nb2/3]O3(x?=?0?~?0.9) ceramics were prepared by the traditional solid-phase reaction sintering...     

Intermediate Temperature Sintering of La-Modified Pb(Zn1/3Nb2/3)O3-PbZrO3-PbTiO3 Piezoelectric Ceramics

In order to realize the co-firing with Ag/Pd electrodes in multilayer devices, Pb(Zn1/3Nb2/3)1-,-yZrxTiyO3(0.25＜x＜0.35, 0.25＜y＜0.35) piezoelectric ceramics (hereafter designated PZN-PZT)modified by La2O3 has been prepared by conventional technique with sintering temperature from 1100℃ to 1140℃. X-ray diffraction patterns demonstrated that pure perovskite phase was obtained. Secondary electron image (SEI) showed that crystalline grains in ceramics were well grown. d33 of manufactured sample was as high as 560×10-12C/N. kp was about 0.61 and tgδabout 30×10-3. The existence of liquid phase examined by electron diffraction in PZN-PZT sample is beneficial to sintering of the ceramic.     

烧结助剂(Y3+、La3+和Mg2+)对半透明氧化铝陶瓷的透光率的影

通过化学沉淀法引入烧结助剂Y³⁺、La³⁺和Mg²⁺, 采用真空烧结工艺制备了半透明Al₂O₃陶瓷, 并研究了烧结助剂对烧结材料的微观结构、相对密度和透光率的影响。结果表明: 引入的烧结助剂能均匀分散在合成的半透明Al₂O₃陶瓷中。烧结助剂的最佳引入量为Mg²⁺(0.15wt%)、Y³⁺(0.05wt%)和La³⁺(0.05wt%), 对应的试样在350~800 nm的波长范围内显示出的最高的总透光率(TFT)高于80%。此外, Y³⁺的掺杂可以促进晶粒生长, 降低孔隙率, 从而提高半透明Al₂O₃陶瓷的透光率。     

Effect of grain size on the strength of Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> optical ceramics

Using micro- and nanoindentation techniques, we have studied the mechanical properties of Y₃Al₅O₁₂ optical ceramics: coarse-grained, prepared by vacuum sintering, and nanostructured, prepared by high-pressure, low-temperature sintering. The effect of grain size on the strength of the ceramics has been analyzed.     

NbO3-LiNbO3无铅压电陶瓷的烧结特性和压电性能研究

采用传统陶瓷烧结工艺制备了（1-x）（K0．5Na0．5）NbO3-xLiNbO3无铅压电陶瓷，研究了陶瓷的结构、烧结特性及电性能特征．制备的（K0．5Na0．5）NbO3-LiNbO3陶瓷为单一的钙钦矿结构，室温下其相结构随LiNbO3含量增加逐渐由正交相向四方相转变，显微结构也由于LiNbO3含量的不同而表现出很大差异．与（K0．5Na0．5）NbO3陶瓷相比，（K0．5Na0．5）NbO3-LiNbO3陶瓷的烧结温度降低，烧结特性得到改善．（K0．5Na0．5）NbO3-LiNbO3陶瓷表现出优越的压电性能，其中0．94（K0．5Na0．5）NbO3—0．06LiNbO3（x=0．06）陶瓷的压电常数d33达到205pC／N，机电耦合系数kp为40．3％，kt达到49．8％．     

Dielectric characteristics of Ba(Mg1/3Ta2/3)O3 ceramics sintered at low temperatures

Dielectric characteristics of Ba(Mg_1/3Ta_2/3)O₃ ceramics (BMT ceramics) sintered at low temperatures with 2–3 wt% NaF additives were determined. A dielectric constant of 25 and extremely low dielectric loss (< 0.0001) were measured at 100 kHz and 1 MHz in BMT ceramics sintered under these conditions, and no frequency dependence of the dielectric constant was observed. This suggested that NaF as sintering additive had no harmful influence on the dielectric properties of the ceramics.     

Grain growth kinetics of textured-BaTiO3 ceramics

Textured BaTiO₃ (BT) ceramics were fabricated by templated grain growth method. Effects of sintering conditions on the grain growth process of textured-BT ceramics were investigated. Orientation degree increased initially and then decreased with increasing soaking time. The ceramics were composed of equiaxed matrix grains and brick-like template particles. The brick-like particles aligned parallel to the casting direction by observing from SEM images. A (h00)-preferred orientation was confirmed by SAED and XRD patterns. Mechanism of grain growth in textured-BT ceramics was studied. Both consumption of matrix by templates and grain growth of templates determined the orientation degree of ceramics. The kinetic mechanism for grain orientation was also discussed by the simplified phenomenological kinetic equation. The average activation energies were 364 kJ/mol for matrix grain and 918 kJ/mol for template particle, respectively. Finally, a dense ceramic with 85% grain orientation was obtained after sintering at 1400 °C for 2 h.     

Nanostructured hydroxyapatite by microwave sintering

In this work, nanostructured HA ceramics with dense microstructure were prepared by microwave sintering process and their microstructures were compared with the case of conventional sintering. Commercially obtained HA powder with Ca/P molar ratio of 1.67 was used as a starting material. The powder of granular type consists of nanocrystalline particles of 20-30 nm in size. The as-received HA powder or the powder calcined at 800 degrees C, followed by ball-milling was used for the preparation of HA disks. Microwave sintering was conducted at 1200 degrees C for 5 min with a heating rate of 50 degrees C/min. HA ceramics with the sintered densities of approximately 96-97% of the theoretical were obtained. XRD analysis showed that all detectable peaks are identical to pure hydroxyapatite. The HA sintered body made of calcined and ball-milled powder showed uniform microstructure with grain size of 300-400 nm and with finer sub-grains of 30-40 nm.     

B2O3蒸汽掺杂的中低温烧结Y-BaTiO3及其PTCR特性研究

通过B2O3蒸汽掺杂,Y-BaTiO3陶瓷的烧结温度大幅度降低．B2O3蒸汽掺杂后的样品,室温电阻率下降,升阻比提高．通过对氧化硼蒸汽掺杂样品的XRD分析研究表明,硼间隙可以在钛酸钡晶格中存在,硼间隙和／或相关缺陷络合物可以形成电子捕获中心,从而提高PTCR效应．     

烧结温度对20%ZrO_2(3Y)/Al_2O_3复相陶瓷力学性能和微观结构的影响

20%纳米ZrO2(3Y)粉末加入到高纯亚微米Al2O3粉中,采用高压干压成型方法和恒速升温多阶段短保温烧结方法制备出不同烧结温度下的复相陶瓷。研究烧结温度对复相陶瓷力学性能的影响,通过XRD,EDS和SEM对复相陶瓷进行元素组成和微观结构分析。结果表明:烧结温度在很大程度上影响着复相陶瓷的力学性能和微观结构,常压烧结1600℃保温8h时,相对密度、维氏硬度和断裂韧性达到最大,分别为98.6%,18.54GPa和9.3MPa·m1/2,而基体晶粒尺寸为1.4~8.1μm,ZrO2相变量为34.6%。1600℃下复相陶瓷具有优质的微观结构,断裂方式为沿晶-穿晶混合断裂模式。ZrO2(3Y)粉体的加入,从相变增韧、内晶型颗粒增韧和裂纹偏转等多个方面提高了复相陶瓷的断裂韧性。     

真空烧结制备(La0.2Nd0.2Sm0.2Gd0.2Er0.2)2Zr2O7高熵透明陶瓷

高熵陶瓷是近年来陶瓷材料研究的热点,制备性能优异的高熵陶瓷是陶瓷材料的发展趋势.本研究采用燃烧法结合真空烧结制备出高熵透明陶瓷.测试结果显示燃烧法制备高熵(La0.2Nd0.2Sm0.2Gd0.2Er0.2)2Zr2O7粉体的平均晶粒尺寸为8 nm,高熵粉体为无序的缺陷萤石结构.在真空炉中不同温度烧结的高熵陶瓷具有有序...     

Solid state and solution synthesis of Ba(Mg1/3Ta2/3)O3: A comparative study

Ba(Mg_1/3Ta_2/3)O₃ [BMT] dielectric ceramics are prepared by solid state (one step, two step and molten salt synthesis) and wet chemical methods (precipitation, citrate gel and sol-gel). The formation mechanism of BMT in each synthesis technique is discussed. The formation temperature and particle size of the formed BMT were found to be much lesser (in nanometer range) for solution synthesized powders. It is found that synthesis by sol-gel method resulted in the formation of ultra pure nanopowders of BMT at about 600 °C with average crystallite size of about 18 nm where as in solid state synthesis the formation of BMT was formed at about 1100 °C with average crystallite size of 220 nm. On sintering these powders, densification and grain growth of the chemically derived powders were found to be lower than that of solid state synthesized BMT powder. This has resulted in a slight decrease in density and microwave dielectric properties of the solution synthesized BMT samples. It is found that the microwave dielectric properties improved with increase in the average grain diameter of the sintered BMT ceramics.     

n-Type nanostructured thermoelectric materials prepared from chemically synthesized ultrathin Bi2Te3 nanoplates

We herein report on the large-scale synthesis of ultrathin Bi(2)Te(3) nanoplates and subsequent spark plasma sintering to fabricate n-type nanostructured bulk thermoelectric materials. Bi(2)Te(3) nanoplates were synthesized by the reaction between bismuth thiolate and tri-n-octylphosphine telluride in oleylamine. The thickness of the nanoplates was ~1 nm, which corresponds to a single layer in Bi(2)Te(3) crystals. Bi(2)Te(3) nanostructured bulk materials were prepared by sintering of surfactant-removed Bi(2)Te(3) nanoplates using spark plasma sintering. We found that the grain size and density were strongly dependent on the sintering temperature, and we investigated the effect of the sintering temperature on the thermoelectric properties of the Bi(2)Te(3) nanostructured bulk materials. The electrical conductivities increased with an increase in the sintering temperature, owing to the decreased interface density arising from the grain growth and densification. The Seebeck coefficients roughly decreased with an increase in the sintering temperature. Interestingly, the electron concentrations and mobilities strongly depended on the sintering temperature, suggesting the potential barrier scattering at interfaces and the doping effect of defects and organic residues. The thermal conductivities also increased with an increase in the sintering temperature because of grain growth and densification. The maximum thermoelectric figure-of-merit, ZT, is 0.62 at 400 K, which is one of the highest among the reported values of n-type nanostructured materials based on chemically synthesized nanoparticles. This increase in ZT shows the possibility of the preparation of highly efficient thermoelectric materials by chemical synthesis.     

Effect of Sn4+ B-Site Substitution on the Microstructure and Dielectric Properties of Ba(Mg1/3Ta2/3)O3 Microwave Ceramics

1.IntroductionRecent progress of microwave telecommunication de-mands the development and application of a variety ofmicrowave dielectric materials.The materials with highdielectric constant(ε),high quality factor(Q)and smalltemperature coefficient of resonant frequency(TCF)haveattracted the greatest interest of researchers.The com-pounds Ba(B'1/3B"2/3)O3(B'=Mg,Zn,Ni,etc.B"=Ta,Nb,etc.)with complex perovskite structure exhibit veryhigh Q value at microwave frequencies greaterthan10GHz.…     

Dielectric, piezoelectric, and ferroelectric properties of MnCO3-added 74(Bi1/2Na}1/2) TiO3-20.8(Bi1/2K1/2)TiO3-5.2BaTiO3 lead-free piezoelectric ceramics

74(Bi1/2Na1/2)TiO{i3}-20.8(Bi1/2K1/2)TiO3-5.2BaTiO3-x MnCO3 lead-free piezoelectric ceramics were synthesized by conventional solid oxide routine. The tetragonal 74(Bi1/2Na1/2)TiO3-20.8(Bi1/2K1/2)TiO3-5.2 BaTiO3 (BNKB) exhibits high depolarization temperature Td of 195°C; however, its properties are far from satisfactory for practical application and need to be improved. The experiments show that the addition of MnCO3 reduces the tetragonality c/a and increases the cell volume. In addition, it revealed that the suitable addition of MnCO3 promotes the sintering and increases the densities of BNKB ceramics. The addition of MnCO3 also enhances the relaxor behavior of BNKB ceramics due to the reconstruct of the disorder arrays. Due to the effect of the crystal lattice, grain growth, and relaxor behavior, the optimal electric properties were realized at MnCO3 addition x of 0.16: the dielectric permittivity εr = 1047, dielectric dissipation tanδ = 0.022, piezoelectric strain d33 = 140 pC/N, mechanical coupling kp = 0.18, mechanical quality Qm = 89 while the depolarization temperature Td stays relatively high at 175°C. The effect and mechanism of Mn doping on the electrical properties were discussed in detail.     

Al_2O_3/B_4C的致密化机制

初始晶粒尺寸为0.33μm和7.0μm的Al2O3/14%B4C粉末在不同温度烧结,并模拟计算陶瓷粉末烧结过程。通过对比实验结果和计算结果,找出影响材料致密化的机制,讨论晶粒尺寸对扩散机制的影响,并估算出致密化激活能。在实验烧结温度范围内,界面反应被认为是影响Al2O3/B4C粉末致密化过程的主要因素。Al2O3/14%B4C陶瓷的致密化激活能是1820±60KJ.mol-1,这结果很大程度上支持界面反应致密化机制。