Polarized Micro-Raman Study of the Temperature-Induced Phase Transition In 0.67 Pb（Mg1/3Nb2/3）O3-0.33PbTiO3

Polarized Raman spectra of ferroelectric relaxor 0.67Pb（Mg1/3Nb2/3）O3-0.33PbTiO3 （0.67PMN-0.33PT） single crystal are systematically investigated in a wide temperature range from -196 to 600℃ by micro-Raman scattering technique. The results clearly reveal that there are two structural phase transitions in such composite ferroelectric relaxor： the rhombohedral-tetragonal （R- T） phase transition and the tetragonal-cubic （T- C） phase transition. The former occurs at about TR-T =34℃, corresponding to the vanishing of the soft A1 mode at 106cm^-1 recorded in the parallel polarization. The latter appears at about TT-C = 144℃, which can be verified with the vanishing of mode at 780cm^-1 measured in the crossed polarization.     

Phase transformation in (0.90−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3-0.10PbZrO3 piezoelectric ceramic: X-ray diffraction and Raman investigation

Piezoelectric ceramics with compositions of (0.90−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃-0.10PbZrO₃, x=0.28, 0.31, 0.34, 0.37, 0.40 and 0.43, were prepared using the conventional columbite precursor method, and their structural phase transformation and piezoelectric behaviors near the morphotropic phase boundary (MPB) have been systematically investigated as a function of PbTiO₃ content. X-ray diffraction (XRD) results demonstrate that the structure of the ceramics experiences a gradual transition process from rhombohedral phase to tetragonal phase with the increasing of PbTiO₃ content, and that compositions with x=0.34-0.40 lie in the MPB region of this ternary system. A Raman spectra investigation of the ceramic samples testified to the transformation process of rhombohedral phase to tetragonal phase by comparing the relative intensities of tetragonal E(2TO₁) mode and rhombohedral phase R_h mode. The structure information was also correlated to the parabola change of the piezoelectric constant; the maximum piezoelectric constants were obtained near the MPB region.     

Effects of Li Substitution and Sintering Temperature on Properties of Bi0.5（Na,K）0.5TiO3 Lead-Free Piezoelectric Ceramics

Bi0.5 （Na0.72K0.28- x Lix ）0.5 TiO3 （BNKLT- 100x） lead-free piezoelectric ceramics are synthesized by conventional solid state sintering techniques. The dielectric and piezoelectric properties of the BNKLT-100x ceramics as a function of Li content are systematically investigated. It is found that not only Li content but also the sintering temperature has a strong effect on the piezoelectric properties of BNKLT. The piezoelectric constant d33 Of BNKLT varies from 120 to 252pC/N in the Li content range from 0.03 to 0.16. In the sintering temperature range from 1080 to 1130℃, the d33 value of BNKLT-6 changes from 200pC/N to 252pC/N. The BNKLT-6 sample sintered at 1100℃ has the highest piezoelectric constant d33 of 252pC/N, with the electromechanical coupling factors kp of 0.32 and kt of 0.44.     

Correlation between Zero-Field Splitting and Site Distortions of Cr^3＋ Ions in NH4Cl：Cr^3＋ System： a Complete Energy Matrix Study

A theoretical method for investigating the inter-relation between the electronic and molecular structures of 3d^3 configuration ions in a tetragonal ligand field is established on the basis of the 120 × 120 complete energy matrices. Using this method, the local structure parameters of two tetragonal Cr^3＋ centers in the NH4 Cl：Cr^3＋ system are determined, Furthermore, the relations between the molecular symmetry and the ligand field symmetry are discussed.     

掺铜PTO晶体顺磁共振谱及局域结构的理论研究

基于晶体场理论,本文采用重叠模型和3d⁹电子组态在畸变四角晶场中的g因子和超精细结构常数A的三阶微扰计算公式以及钛酸铅PbTiO₃ (PTO): Cu²⁺晶体的局域结构与EPR谱之间的定量关系,合理解释了PTO: Cu²⁺晶体的EPR谱及局域晶体结构,所得结果与实验观测相符合.      

Numerical Calculation of SAW Propagation Properties at the x-Cut of Ferroelectric PMN-33%PT Single Crystals

Surface acoustic wave （SAW） properties at the x-cut of relaxor-based 0.67Pb（Mg1/3Nb2/3）O3-0.33PbTiO3 （PMN- 33%PT） ferroelectric single crystals are analyzed theoretically when poled along the [001]c cubic direction. It can be found that PMN-33%PT single crystal is a kind of material with a low phase velocity and high electromechanical coupling coefficient, and the single crystal possesses some cuts with zero power flow angle. The results are based on the material parameters at room temperature. The conclusions provide device designers with a few ideal cuts of PMN-33%PT single crystals. Moreover, choosing an optimal cut will dramatically improve the performance of SAW devices, and corresponding results for crystal systems working at other temperatures could also be figured out by employing the method.     

Electrical Characterization of Deep Trap Properties in High-k Thin-Film HfO2 Dielectric

Deep-trap properties of high-dielectric-constant （k） HfO2 thin films are investigated by deep-level transient spectroscopy and capacitance-voltage methods. The hole traps of the HfO2 dielectric deposited on a p-type Si substrate by sputtering are investigated in a metal-oxide-semiconductor structure over a temperature range of 300-500K. The potential depth, cross section and concentration of hole traps are estimated to be about 2.5eV, 1.8 ×10^-16 cm^2 and 1.0 × 10^16 cm^-3, respectively.     

晶体PZCST:VO2+的EPR谱及光吸收谱的理论研究

采用双旋-轨耦合参量模型和3d¹电子组态在四角对称下的能级公式,计算了KZnClSO₄·3H₂O(PZCST): VO²⁺的EPR谱和光吸收谱,所得EPR谱和光吸收谱的理论结果与实验发现符合得很好. 研究发现,该晶体沿C₄轴局域对称结构呈压缩的四角畸变,其大小为0.47 nm;大的κ值表明VO²⁺的未配对电子的自旋极化对超精细结构常数有着较大的贡献.     

Atomic Diffusion in Cu/Si （111） and Cu/SiO2/Si （111） Systems by Neutral Cluster Beam Deposition

The Cu films are deposited on two kinds of p-type Si （111） substrates by ionized duster beam （ICB） technique. The interface reaction and atomic diffusion of Cu/Si （111） and Cu/SiO2/Si （111） systems are studied at different annealing temperatures by x-ray diffraction （XRD） and Rutherford backscattering spectrometry （RBS）. Some significant results are obtained： For the Cu/Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230℃. The diffusion coefficients of the samples annealed at 230℃ and 500℃ are 8.5 ×10^-15 cm^2.s^-1 and 3.0 ×10^-14 cm^2.s^-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2//Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450℃. The diffusion coefficients of Cu in Si are calculated to be 6.0 ×10^-16 cm^2.s^-1 at 450℃, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.     

The Average Lifetime of Giant Composite Systems Formed in Strongly Damped Collisions

The dynamic, adiabatic and diabat ic entrance potentials in strongly damped reactions of ^238 U＋^238 U, ^232 Th ＋ ^250Cf are calculated and compared. The feature of the dynamical potential implies that it is possible for the composite systems to stick together for a period of time. By means of the improved quantum molecular dynamics model the time evolution of the density and charge distributions of giant composite systems and their fragments for reactions ^238U＋^238U, ^232Th＋^250Cf are investigated, from which the lifetimes of giant composite systems at different energies are obtained. The longest average lifetime of ^238U＋^238U is found when the incident energy is about Ec.m =1080 MeW, which is about 1200 fm/c.     

Chiral Lagrangian Treatment of 0^＋＋ Mesons and 0^＋＋ Glueballs

Within the framework of a nonlinear chiral Lagrangian the mass spectra and the decay properties of 0^＋＋ states below 2 GeV are studied. Assuming that f0（980）, a0（980）, K0（1430）, and f0（1500） comprise an SU（3） nonet, we make a detailed prediction about the static properties of the 0^＋＋ mesons. The substructure analysis of these states in terms of two- and four-quark components as well as a glueball component is carried out. We also consider the interaction Lagrangian and provide a preliminary study of the strong and radiative decays of the 0＋＋ mesons. The scalar glueball masses and partial widths are also presented. In view of the fact that few data of 0＋＋ mesons are clearly given in the present PDG （Particle Data Group） list and that the four-quark content of mesons is a hot issue both experimentally and theoretically, the predicted results of the paper may be helpful for upcoming experimental and theoretical studies of these mesons.     

Phenomenological Scaling of Rapidity Dependence for Anisotropic Flows in 25 MeV/nucleon Ca＋Ca by Quantum Molecular Dynamics Model

Anisotropic flows （v1, v2, v3 and v4） of light fragments up to the mass number 4 as a function of rapidity are studied for 25 MeV/nucleon ^40Ca ＋ ^40Ca at large impact parameters by a quantum molecular dynamics model. A phenomenological scaling behaviour of rapidity dependent flow parameters vn （n = 1, 2, 3 and 4） is found as a function of mass number plus a constant term, which may arise from the interplay of collective and random motions. In addition, v4/v2^2 keeps to be almost independent of rapidity and remains a rough constant of 1/2 for all light fragments.     

KNN Based Lead-Free Piezoceramics with Improved Thermal Stability

Lead-free piezoelectric ceramics （1 - x） （Na0.53K0.404 Li0.066）Nb0.92 Sb0.08 03 ＋xZrTiO3 are fabricated by conventional solid-state sintering method, and their dielectric and piezoelectric characteristics are investigated. With the addition of SrTiO3, the growth of the grain size is restrained, meanwhile the phase transition temperature of orthorhombic-tetragonal is shifted below room temperature. It is found that the ceramics with x = 0.010 exhibit excellent piezoelectric properties （d33 = 220 pC/N, kp = 41%, kt = 39%） and improved thermal stability around room temperature. The results indicate that these materials are promising lead-free piezoceramics for practical operations.     

Phase transition, structural and electrical properties of Pb(Zn1/3Nb2/3)O3-doped Pb(Ni1/3Nb2/3)O3-PbTiO3 ceramics prepared by solid-state reaction method

Phase pure perovskite (1−x−y)Pb(Ni_1/3Nb_2/3)O₃-xPb(Zn_1/3Nb_2/3)O₃-yPbTiO₃ (PNN-PZN-PT) ferroelectric ceramics were prepared by conventional solid-state reaction method via a B-site oxide mixing route. The PNN-PZN-PT ceramics sintered at the optimized condition of 1185 °C for 2 h exhibit high relative density and rather homogenous microstructure. With the increase of PbTiO₃ (PT) content, crystal structure and electrical properties of the synthesized PNN-PZN-PT ceramics exhibit successive phase transformation. A morphotropic phase boundary (MPB) is supposed to form in (0.9−x)PNN-0.1PZN-xPT at a region of x=32-36 mol% confirmed by X-ray diffraction (XRD) measurement and dielectric measurement. The MPB composition can be pictured as providing a “bridge” connecting rhombohedral ferroelectric (FE) phase and tetragonal one since crystal structure of the MPB composition is similar to both the rhombohedral and tetragonal lattices. Dielectric response of the sintered PNN-PZN-PT ceramics also exhibits successive phase-transition character. 0.64PNN-0.1PZN-0.26PT exhibits broad, diffused and frequency dependent dielectric peaks indicating a character of diffused FE-paraelectric (PE) phase transition of relaxor ferroelectrics and 0.40PNN-0.1PZN-0.50PT exhibits narrow, sharp and frequency independent dielectric peaks indicating a character of first-order FE-PE phase transition of normal ferroelectrics. The FE-PE phase transition of 0.56PNN-0.1PZN-0.34PT is nearly first-order with some diffused character, which also exhibits the largest value of piezoelectric constant d₃₃ of 462pC/N.     

Artificial Modulation of Ferroelectric Thin Films into Antiferroelectric through H+ Implantation for High-Density Charge Storage

Hydrogen ions are implanted into Pb（Zro.3Tio.7）03 1014 ions/cm^2. Pseudo-antiferroelectric behaviour in thin films at the energy of 40keV with a flux of 5 x the implanted thin films is observed, as confirmed by the measurements of polarization versus electric hysteresis loops and capacitance versus voltage curves. X-ray diffrac- tion patterns show the film structures before and after H＋ implantation both to be perovskite of a tetragonal symmetry. These findings indicate that hydrogen ions exist as stable dopants within the films. It is believed that the dopants change domain-switching behaviour via the boundary charge compensation. Meanwhile, time dependence of leakage current density after time longer than lOs indicates the enhancement of the leakage cur- rent nearly in one order for the implanted film, but the current at time shorter than i s is mostly the same as that of the original film without the ionic implantation. The artificial tailoring of the antiferroelectric behaviour through H＋ implantation in ferroelectric thin films is finally proven to be achievable for the device application of high-density charge storage.     

Effects of Interfacial Polarization on Voltage Tunability of Pb(Fe1/2Nb1/2)1-xTixO3 Single Crystals

The voltage tunability of Pb(Fe_1/2Nb_1/2)_1-xTi_xO₃ single crystals is investigated at a low electric field (<130 V/cm) in a low frequency range (<1 MHz). The results show that the capacitance is strongly suppressed by the applied dc biases for both the rhombohedral sample and the tetragonal sample. A negative voltage tunability is only detected in the tetragonal sample. The origin of the giant tunability and the negative tunability is discussed based on the multipolarization-mechanism model and the equivalent circuit model, respectively. It is ascribed to the interfacial polarization at the interface of electrode/sample.     

Dielectric, piezoelectric and elastic properties of tetragonal BiScO3-PbTiO3 single crystal with single domain

Modified BiScO₃-PbTiO₃ (BSPT) tetragonal single crystals were grown using high temperature solution method. The dielectric, piezoelectric and elastic properties of single domain BSPT crystals, after poling along [001] crystallographic direction, have been determined experimentally using the resonance method. The results showed that the BSPT tetragonal crystals possess good piezoelectric properties, with electromechanical coupling factor about 88% and piezoelectric coefficient over 400 pC/N at room temperature. BSPT tetragonal crystals have high Curie temperature around 436 °C and high coercive field ∼28 kV/cm, also, the crystal exhibited a very good temperature stability of the properties till 380 °C. For comparison, the material constants of tetragonal Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ (PZNT) single crystals were measured and listed in this paper.     

（Na0.52K0.44Li0.04）Nb0.9-xSbxTa0.1O3 Lead-Free Piezoelectric Ceramics with High Performance and High Curie Temperature

（Na0.52K0.44Li0.04）Nb0.9-x Sbx Ta0.1O3 lead-free piezoelectric ceramics are prepared by a solid-state reaction method. With increasing Sb content, the transition temperature from orthorhombic to tetragonal polymorphic phase decreased. A composition （Na0.52K0.44Li0.04）Nb0.863Sb0.037Ta0.1O3 is found to possess excellent piezo- electric and electromechanical performances （d33 = 306pC/N, kp =48%, and kt=50%）, and high Curie temperature （Tc = 320 ℃）. These results indicate that （Na0.52K0.44Li0.04）Nb0.863Sb0.037 Ta0.1O3 is a promising lead-free piezoceramics replacement for lead zirconate titanate.     

Structural and microwave properties of (Ba,Sr)TiO3 films grown by pulsed laser deposition

The relationship between the structure and the microwave dielectric properties of epitaxial Ba_0.5Sr_0.5TiO₃ (BST) films has been investigated. Single-phase BST films (40-160 nm) have been deposited onto (100) MgO substrates by pulsed laser deposition. As-deposited films show a significant tetragonal distortion. The in-plane lattice parameters (a) are always larger than the surface normal lattice parameters (c). The tetragonal distortion depends on the thickness of the films and the post-deposition annealing conditions. Films annealed at 900 °C show less tetragonal distortion than the as-deposited film and the films annealed at higher temperatures. The distortion in the film is due to stress caused by the lattice mismatch and thermal expansion coefficient differences between the film and the substrate. The dielectric constant and its change with dc bias voltage of BST films on MgO at microwave frequencies increase with increasing annealing temperature from 900 °C to 1200 °C, which corresponds to an increase in the tetragonal distortion.     

纳米离子导体在流体静压力下的复阻抗谱研究

 用惰性气体蒸发和真空原位加压方法制备了具有清洁界面的平均粒度16 nm的纳米固体CaF₂，并在0.1~2 400 MPa范围不同的静水压下用100 kHz~100 Hz内70种频率，精确测量了纳米CaF₂的复平面阻抗谱。分别给出纳米CaF₂离子电导率和相对介电常数随流体静压力的变化规律。最后的讨论指出：离子迁移通遭受压后的变化（大于、等于或小于最佳值）是影响离子电导率-压力曲线的主要因素；界面层空间电荷极化是造成纳米CaF₂相对介电常数较大的原因，由此界面效应可理解介电常数-压力曲线。