Dielectric characteristics of CaCu3Ti4O12/P(VDF-TrFE) nanocomposites

Composite thin film is highly desirable for the dielectric applications. In order to develop composite thin film, a nanocomposite, in which nanosized CaCu₃Ti₄O₁₂ (CCTO) particles are used as filler and P(VDF?CTrFE) 55/45 mol% copolymer is used as polymer matrix, is investigated. The contents of CCTO in the nanocomposites range from 0% to 50?vol%. The dielectric property of these nanocomposites was characterized at frequencies ranging from 100 Hz to 1 MHz and at temperatures ranging from 200 K to 370 K. A dielectric constant of 62 with a loss of 0.05 was obtained in nanocomposite with 50?vol% CCTO at room temperature at 1 kHz. At the phase transition temperature (??340?K) of the copolymer, a dielectric constant of 150 with a loss less than 0.1 was obtained in this nanocomposite. It is found that the dielectric loss of the nanocomposites is dominated by the polymer which has a relaxation process. Comparing to composites made using microsized CCTO, the nanocomposites exhibit a much lower dielectric loss and a lower dielectric constant. This indicates that the nanosized CCTO particles have a lower dielectric constant than the microsized CCTO particles.     

Fabrication of Gd0.5Sr0.5CoO3 film for SOFC cathode by pulsed laser deposition

Gd_0.5Sr_0.5CoO₃ (GSCO) film has been fabricated by pulsed laser deposition (PLD) to be used as the cathode of the solid oxide fuel cell (SOFC). The GSCO thin film obtained has a columnar crystalline structure so that it will have a high permeation property. The PLD technique has been found suitable for growing a film of complex composition because of its good control of stoichiometry and thus for fabricating a GSCO film used as the cathode of the SOFC. The GSCO film has been studied for porosity electrical conductivity and power density. The GSCO film grown at a substrate temperature of 1100 K and oxygen gas pressure of 100 Pa has high electrical conductivity which is 820 S cm^− 1 at 973 K with post annealing at a rather low temperature (1000 K). This value is higher than that of the GSCO film prepared by RF-sputtering with post annealing at a higher temperature (1273 K).     

脉冲强磁场下的电极化测量系统

多铁性材料是当前物质科学研究的热点,具有重要的科学研究意义和应用前景.低温和强磁场实验环境为研究多铁性材料提供了一种有效途径.脉冲强磁场下的电极化测量系统能实现最高磁场强度60 T、最低温度0.5 K的铁电特性测量.该系统采用热释电方法,具有磁场强度高、控温范围广、转角测量等特点,可用于强磁场下的磁电特性研究.本文介绍了该系统的测量装置和实验原理,并展示了其在多铁性材料研究中的一系列应用,揭示了脉冲强磁场电极化测量系统在磁电特性探索中的重要作用.     

Synthesis and dielectric characteristics of La0.5Bi0.5MnO3 ceramics

La_0.5Bi_0.5MnO₃ ceramics with a single phase were prepared by a solid-state reaction method, and their dielectric properties were characterized. Two dielectric relaxations with a giant dielectric constant were identified in the temperature range from 125 to 350 K. The electron hopping between Mn³⁺ and Mn⁴⁺ was found to be the origin of the dielectric relaxation at low temperatures (125–200 K) with an activation energy of 0.18 eV. The high temperature (200–350 K) dielectric relaxation can be attributed to the conduction.     

温度相关的微波频率下氯化钠水溶液介电特性

针对NaCl水溶液(0.001–0.5 mol/L)介电特性, 实验调查了频率(200–6.25 GHz), 温度(293–353 K)、 浓度相关复介电常数. 结果表明: 频率增大的过程中虚部呈逐渐减小的趋势, 高温使离子扰动增大, 破坏了溶液内部水分子四面体结构和氢键构象而使介电常数实部减小. 与纯水相比, 溶液的损耗角正切在高温353 K低频区下降明显. 同时发现2.45和5.8 GHz的复介电常数随温度变化的温度窗效应, 温度窗效应导致微波加热时耗散功率的振荡变化, 温度分布不均匀现象在实验中得以证实. 关键词： 微波 复介电常数 介电特性 高温探头     

Pressure and temperature dependence of the static dielectric constant of KBr

The static dielectric constant and the temperature and pressure derivatives of the static dielectric constant of KBr have been measured at several temperatures between 4·3°K and room temperature. The sample was prepared in the form of a three-terminal parallel-plate capacitor and the dielectric constant was determined from measurements of the capacitance with a high precision bridge. The dielectric constant decreases with temperature as does the magnitude of the temperature dependence and the magnitude of the pressure dependence. The data were used to calculate the fixed-volume temperature derivative of the dielectric constant. This quantity, (? ln ε/?T)_v, exhibiting lattice-anharmonicity effects, decreases slightly from its room temperature value as the temperature is lowered, rises to a maximum value at about 33°K and then decreases rapidly at lower temperatures.     

Specific Features of the Structure and the Dielectric Properties of Sodium–Bismuth Titanate-Based Ceramics

The phase formation, specific features, and the dielectric properties of the ceramics of compositions from the region of morphotropic interface in the (Na_0.5Bi_0.5)TiO₃–BaTiO₃ system modified by Bi(Mg_0.5Ti_0.5)O₃ and also low-melting additions KCl, NaCl–LiF, CuO, and MnO₂ that favor the control of the stoichiometry and the properties of the ceramics have been studied. The ceramics are characterized by ferroelectric phase transitions that are observed as jumps at temperatures near 400 K and maxima at T_m ~ 600 K in the temperature dependences of the dielectric permittivity. The phase transitions at ~400 K demonstrate the relaxor behavior indicating the existence of polar domains in the nonpolar matrix. An increase in the content of Bi(Mg_0.5Ti_0.5)O₃ favor a decrease in the electrical conductivity and dielectric losses of the samples, and the relative dielectric permittivity at room temperature ε_rt is retained quite high, achieving the highest values ε_rt = 1080–1350 in the ceramics modified with KCl.     

Bi0.5Ba0.5Fe0.5Ti0.49Nb0.01O3热敏陶瓷的微结构和电学性能研究

采用固相合成工艺,制备了Bi_05Ba_05Fe_05Ti_049Nb_001O₃（BBFTN）热敏陶瓷,借助X射线衍射仪、扫描电子显微镜、阻温测试仪和交流阻抗谱考察其微结构、直流电阻、介电特性、阻抗和电学模量方面的电学性能. 结果表明：BBFTN材料依然为立方钙钛矿结构,平均晶粒尺寸约为10 μm,晶格常数相对于BaTiO₃的晶格常数有所变大;室温电 关键词： 05Ba_05Fe_05Ti_049Nb_001O₃')" href="#">Bi_05Ba_05Fe_05Ti_049Nb_001O₃ 微结构 电学性能     

Equations of state of MgO at high pressure and temperature

Abstract

A synchrotron X-ray diffraction study on MgO has been done at simultaneous high pressure and temperature. The lattice parameter of MgO has been measured up to a static pressure of 6 GPa and a temperature of 1273 K, using a large volume pressure cell and energy-dispersive synchrotron X-ray powder diffraction. The compression was made following six high-temperature isotherms. A Vinet equation of state was used to fit the experimental P-V-T data. The Vinet's model compares very well with the experimental data above the Debye temperature (760 K) and allows the use of MgO as an alternative internal pressure calibrant for experiments at high temperature.     

激光消光法测量甲苯高温裂解的碳烟产率

建立了碳氢燃料在反射激波作用下高温裂解碳烟生成的检测系统,利用激光消光法测量了甲苯/氩气在高温条件下裂解生成碳烟的产率。实验条件：甲苯摩尔浓度0.25%和0.5%,压力约2和4 atm,温度1 630～2 273 K。获得了碳烟产率随温度、压力和燃料浓度的变化规律。碳烟产率随温度变化呈高斯分布,随着压力或浓度的增大,碳烟产率增大,碳烟产率最大达55%。产率的峰值温度随压力变化不大,但甲苯摩尔浓度从0.25%增大到0.5%时,峰值温度从1 852变为1 921 K。对比了压力为4 atm,燃料摩尔浓度为0.5%的甲基环己烷和甲苯的碳烟产率,甲基环己烷裂解碳烟产率峰值对应的温度为2 045 K,比甲苯约高135 K,但其最大碳烟产率仅有甲苯的1/8。结果为研究发动机内碳烟颗粒物排放及碳烟形成机理提供了实验依据。     

Effect of Annealing on Ferroelectric Properties of Nanometre BaTiO3 Ceramics Prepared by High Pressure Sintering Method

Dense nanocrystalline BaTiO3 ceramics with a grain size of 5Onto are prepared under 6 GPa at 1273K using a high pressure sintering method. The sintered bulk is uniform and the relative density is above 97%. We anneal the ceramic samples in oxygen with various temperatures and for the annealing, several broadened peaks can be observed at different times without apparent grain growth. After about 378K（ by dielectric measurements. However, these peaks are very different from those of coarser-grained ceramics. It is indicated that both the elimination of oxygen vacancies and the release of residual stresses caused by high pressure greatly improve the overall ferroelectric properties of BaTiO3 ceramics. The observation of nearly linear polarization hysteresis loop after anneal provides the solid evidence of ferroelectricity in these nano-sized BaTiO3 ceramics. It is believed that the absence of 90° domains and the existence of poor-permittivity nonferroelectric grain boundaries contribute to the slim loop.     

氦离子注入4H-SiC晶体的纳米硬度研究

4H-SiC晶体经能量为100 keV,剂量为3×10¹⁶ cm^-2的氦离子高温（500 K）注入后,再在773—1273 K温度范围内进行了退火处理,最后使用纳米压痕仪测量了样品注入面的硬度.测试结果表明,在500—1273 K温度范围内样品的硬度随退火温度升高呈现先增大后减小再增大的趋势,其中773 K退火样品的硬度增大明显.分析认为,退火样品的硬度变化是由退火过程中缺陷复合与氦泡生长导致样品内部的Si—C键密度、键长和键角改变引起的. 关键词： SiC 注入 氦泡 纳米压痕     

Room-temperature multiferroic properties of Bi4.15Nd0.85Ti3FeO15 thin films prepared by the metal–organic decomposition method

Aurivillius-structured Bi_4.15Nd_0.85Ti₃FeO₁₅ multiferroic thin films with four perovskite slabs were deposited on Pt/Ti/ SiO₂/Si substrates by the metal–organic decomposition method. The structural, dielectric and multiferroic properties of the films were investigated. Good ferroelectric behavior along with large dielectric constant and small loss factor were observed at room temperature. A weak ferromagnetic rather than an antiferromagnetic property was observed at room temperature by magnetic measurement. Moreover, the ferromagnetic property was enhanced when the temperature was below 13 K and a large saturation magnetization of about 5.4 emu/cm³ was obtained at 4 K. Possible reasons are put forward to discuss the complicated magnetic property.     

Ordering of polarons in Pr0.5Ca0.5MnO3

We report detailed dielectric investigations of Pr_1?xCa_xMnO₃ (PCMO, x=0.5) ceramics, a member of the perovskite manganite family that exhibits a colossal magnetoresistance. Analysis of the electrical conductivity and dielectric constant data revealed that in the low temperature phase, below 42 K, small polarons are responsible for the charge transport in the system. This provides a new understanding of the phase diagrams in PCMO systems     

高温高压下β相硼的电导率测量

 硼在高压下具有复杂的结构和多样的物理性质,对其结构和性质的深入研究具有很重要的意义,一直引起理论和实验研究领域的关注。高压下进行电学性质测量是获得物质物理性质的有效手段,利用集成在金刚石对顶砧上的微电路,在高压下和两个不同温度范围内对β相硼进行了电导率测量,分析了导电机制随压力的变化规律。在0～28.1 GPa范围内,β相硼的电导率随着压力的增大是逐渐增大的,卸压后样品的电导率不能回到最初的状态,是一个不可逆的变化过程;由室温到423 K的范围内,β硼的电导率随着温度的不断增加有明显的上升趋势,并且随着压力的升高,电导率变化逐渐加快。此外,对样品在14.5 GPa和18.6 GPa压力下,用溅射到金刚石对顶砧上的氧化铝薄膜做绝热层,对样品进行了激光加热实验,最高温度达到2 224 K,电导率随着温度的上升而增大,结果显示,β相硼的电学特征仍然属于半导体的特征范围内。     

Synthesis and Structural Characterization of a New Phase of GaAsO 4

A new polymorph of GaAsO 4 has been synthesised at high pressure and temperature (60 kbar and 1273 K). Samples were characterised by powder X-ray diffraction, scanning electron microscopy and EDAX spectroscopy. This material shows an hexagonal symmetry with cell parameters, a =8.1931(4) Å and c =4.3744(2) Å; particles are of hexagonal shape with a narrow size distribution around 2-3 w m and composition close to the Ga:As atomic ratio=1:1. This new high pressure phase of GaAsO 4 represents a new transition path for the ABO 4 compounds.     

Space-charge relaxation and electrical conduction in?K0.5Na0.5NbO3 at high temperatures

Sodium potassium niobate K_0.5Na_0.5NbO₃(KNN) ceramic was synthesized by a solid-state technique. The X-ray diffraction of the sample at room temperature showed a monoclinic phase. The real part (ε′) and imaginary part (ε″) of dielectric permittivity of the sample were measured in a frequency range from 40 Hz to 1 MHz and in a temperature range from 350 to 850 K. The ε′ deviated from Curie–Weiss law above 702 K, due to additional dielectric contributions resulting from universal dielectric response and thermally activated space charges at high temperatures. This anomaly arose from a Debye dielectric dispersion that slowed down following an Arrhenius law. We have established a link between the dielectric relaxation and the conductivity.     

Thermoelastic behaviour of hexagonal graphite-like boron nitride

Abstract

A synchrotron X-ray diffraction study on hexagonal graphite-like boron nitride (h-BN) was performed under high pressures and temperatures. From the measured P-V-Trelation for h-BN (with a three-dimensional ordering parameter P₃ = 0.9) in the temperature range from 298 to 1273 K and up to 6.7 GPa, the thermoelastic parameters are derived by fitting a modified high temperature Birch-Murnaghan equation of state. The results are: bulk modulus B₀[GPa] = 27.6-0.0081(T[K]-298) and its pressure derivative B¹ = 10.5 + 0.0016(T [K] - 298). These values are for samples with P₃ = 0.9 and are quite different for samples with different values of the order parameter. This parameter is shown to have a leading role in the determination of the thermoelastic properties of h-BN, which explains and reconciles the differences between previous results.     

A comparative study of magnetic and dielectric behaviors for La(1-x)Bi(x)Mn(1-y)Fe(y)O3 series (with x = 0.5, 0.7 and y = 0.3, 0.7)

We have carried out an extensive investigation into the effect of doping on both the A- and B-sites for the multiferroic La(0.5)Bi(0.5)Mn(0.5)Fe(0.5)O(3) in relation to its physical properties. The temperature dependent magnetization and dielectric response are determined for different percentages of Bi- and Fe-substitutions. For La(0.5)Bi(0.5)Mn(0.7)Fe(0.3)O(3), there is a prominent ferromagnetic transition T(C) around 110 K, whereas the other La(0.5)Bi(0.5)Mn(0.3)Fe(0.7)O(3) and La(0.3)Bi(0.7)Mn(0.3)Fe(0.7)O(3) phases fail to exhibit any clear transition. On the other hand, for the Fe-rich phases, the coercive field increases to 2450 Oe compared to 1720 Oe (for the Mn-rich phase). All the compositions exhibit coexistence of ferromagnetic and antiferromagnetic phases at low temperatures. The temperature dependent dielectric constant of the investigated samples varies from 32,000 to 500 at room temperature and the data has been analyzed using the universal dielectric response model.     

高温空气在蜂窝陶瓷体内蓄热特性研究

采用数值模拟方法对不同孔隙率和孔壁厚的蜂窝陶瓷体的蓄热特性进行研究。对高温空气在不同结构的蜂窝陶瓷体内流动过程中的压降、温度及蜂窝陶瓷体的蓄热特性进行了分析。研究结果表明：流体在蜂窝陶瓷内流动时,处于层流阶段的压降仅为湍流情况下的1／10。蜂窝陶瓷蓄热体的蓄热时间与蓄热体的孔壁厚成正比。蓄热体孔壁厚h=2mm时,出口空...