Thermal,Raman and dielectric study of 0.5K0.5Bi0.5TiO3–0.5PbTiO3 ceramics

The 0.5K_0.5Bi_0.5TiO₃–0.5PbTiO₃ ceramics were prepared by following a standard solid-state method. The Raman, thermal and dielectric properties of these ceramics were investigated. The X-ray measurements showed that samples have single perovskite-type structure with tetragonal symmetry. Dielectric study revealed that the dielectric behaviour of the investigated ceramics is rather of normal ferroelectrics with large thermal hysteresis. The transition temperature observed by means of differential scanning calorimetry measurements is in good agreement with that obtained from dielectric study.     

0.5PZN-0.5PZT压电陶瓷拉曼散射研究

PZT基多元系压电陶瓷在三方相含量与四方相含量相等的准同型相界处(MPB)具有极为优异的压电性能。文章采用拉曼散射方法研究了0.5PZN-0.5PZT陶瓷体系中三方-四方相共存与弥散相变现象。研究发现,与纯PZT相比,0.5PZN-0.5PZT体系拉曼谱呈明显宽化特征,表明体系弛豫性较强,依据介温谱计算出弥散因子γ高达1.71。通过对拉曼谱峰进行Gauss函数拟合,定量计算三方相R₁模式与四方相E(3TO)和A₁(3TO)模式相对强度,以及四方相E(4LO)和A₁(3LO)模式与三方相R_h模式相对强度,结果表明0.5PZN-0.5PZT体系三方相与四方相含量相等,组成位于准同型相界,该结果得到XRD相分析验证。电学测量表明0.5PZN-0.5PZT陶瓷压电性能优异：k_p=0.66, d₃₃=425 pC/N,适宜作为压电致动器材料使用。     

Effect of cooling method on the electrochemical performance of 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2 cathodes

0.5Li₂MnO₃·0.5LiNi_0.5Mn_0.5O₂ powders were synthesized by coprecipitation, and high temperature sintered with different cooled methods, such as cooled with furnace material, water material, and in liquid nitrogen (N-material). The effect of cooling methods on physical and electrochemical properties are discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy, electrochemical impedance spectroscopy (EIS), and discharge, cyclic, and rate tests. XRD results show that all samples exhibit layered characteristics. The electrochemical performance results indicate that the N-material has the best electrochemical performance. The discharge capacity at 0.1 and 5 C are 279 and 99 mAhg^?1, respectively. The coulomb efficiency is highest, 78.4 %. The capacity retention after 50 cycles at 0.2 C is 97.1 %. EIS results show that the charge transfer resistance of N-materials is lowest, which is responsible for higher rate capacity.     

Magnetic properties of Nd0.5Pb0.5-xSrxMnO3 materials

The structure and magnetic properties of Nd0.5Pb0.5-xSrxMnO3 (0≤x≤0.4) manganites were systematically investigated. Significant changes in Curie temperature and metal-insulator (MI) transition temperature of the samples were observed. All samples exhibited a transition from paramagnetic semiconducting to ferromagnetic metallic state.Curie temperature Tc and the MI transition temperature Tp increased with increasing Sr content. We attributed these behaviours to the enhancing of both the double exchange mechanism and the Jahn-Teller electron-phonon coupling.     

Microstructure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–LiNbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of (1?x?y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yLiNbO₃ (BNT–BKT–LN-x/y) have been fabricated by a conventional solid-state reaction method, and their microstructure and electrical properties have been investigated. The results of X-ray diffraction (XRD) measurement show that K⁺, Li⁺ and Nb⁵⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a pure perovskite structure. The BKT and LN addition has no remarkable effect on the crystal structure. However, a significant change in grain size took place. Simultaneously, with increasing amount of LN, the temperature for a ferroelectric–antiferroelectric phase transition is clearly reduced. The temperature dependence of dielectric properties suggests that the ceramics have diffuse-type phase transition characteristics. The piezoelectric constant d₃₃ and the electromechanical coupling factor k_p of the ceramics attain maximum values of 195 pC/N and 0.336 at x=0.18 and y=0.01.     

Diffuse dielectric anomaly of （Na0.5K0.5Bi）0.5TiO3 crystal at high temperature

This paper investigates the dielectric properties of (Na_0.5K_0.5Bi)_0.5TiO₃ crystal at intermediate frequencies (1kHz \le f \le 1MHz) in the temperature range of 30--560℃. A pronounced high-temperature diffuse dielectric anomaly has been observed. This dielectric anomaly is shown to arise from a Debye-like dielectric dispersion that slows down following an Arrhenius law. The activation energy E_r obtained in the fitting process is about 0.69eV. It proposes that the dielectric peak measured at low frequency above 400℃ is not related to the phase transition but to a space-charge relaxation.     

Magnetic properties of Nd0.5Pb0.5—xSrxMnO3 materials

The structure and magnetic properties of Nd_{0.5}Pb_{0.5-x}Sr_xMnO_3 (0≤x≤0.4) manganites were systematically investigated. Significant changes in Curie temperature and metal-insulator (MI) transition temperature of the samples were observed. All samples exhibited a transition from paramagnetic semiconducting to ferromagnetic metallic state. Curie temperature T_C and the MI transition temperature T_p increased with increasing Sr content. We attributed these behaviours to the enhancing of both the double exchange mechanism and the Jahn－Teller electron－phonon coupling.     

Ferroelectric relaxor properties of (1 − x)K0.5Na0.5NbO3–xBa0.5Ca0.5TiO3 ceramics

The Ba_0.5Ca_0.5TiO₃ (BCT) composition dependent dielectric and structural properties of (1?x)K_0.5Na_0.5NbO₃–xBa_0.5Ca_0.5TiO₃ powders were investigated. Room temperature x-ray diffraction revealed the powder structure to transform from orthorhombic to cubic with increasing BCT composition. The frequency dependent dielectric constant measurements revealed a shift in the temperature of the maximum dielectric constant for at frequencies, suggesting that the system exhibits ferroelectric relaxor behavior. The system containing 15% BCT showed the closest calculated Curie–Weiss exponent to 2, which the exponent for a relaxor ferroelectric.     

La0.5Ca0.5-xBaxMnO3体系中的异常磁电阻行为

实验研究了La0.5Ca0.5MnO3系统Ca位上Ba掺杂对其磁电阻效应的影响.结果表明,掺杂量低于0.2的样品,磁电阻效应随温度降低而增大,在转变温度附近达到最大值,然后随温度降低而变小,随着温度进一步降低磁电阻效应再次增大.而对于掺杂量高于0.2的样品,磁电阻效应在整个温区随温度降低而单调增加.文中通过考虑铁磁性和反铁磁性两种效应的竞争而对实验观察给出解释.     

SrFCl0.5Br0.5:Sm2+的延迟荧光现象

本文报道了ＳｒＦＣｌ０．５Ｂｒ０．５：Ｓｍ＾２＋材料中Ｓｍ＾２＋的荧光光谱，并由光谱中几个较强的荧光峰的时间分辨光谱得到荧光的寿命。通过对连续光激发的荧光谱与脉冲光激发的荧光谱的比较发现了延迟光现象。并对不同延时时间的光谱作了比较，并进一步分析了延迟荧光产生的原因是来源于各辐射荧光的上能级粒子数布局方式的不同造成的。     

Dielectric and piezoelectric properties of Li-substituted lead-free (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3–BaTiO3 ceramics

Lead-free 0.79(Bi_0.5Na_0.5)TiO₃–0.14[Bi_0.5(K_0.5−xLi_x)]TiO₃–0.07BaTiO₃ (BNBK79 + xLi, x = 0.0, 0.1, 0.2, 0.25, 0.3, and 0.4) ceramics were prepared by conventional solid state reaction process. The crystalline structures and surface morphologies are investigated by X-ray diffraction method and scanning electron microscopy. Dielectric and piezoelectric properties were measured. With increasing of lithium substitution, the Curie temperatures of BNBK79 + xLi ceramics increase, but the maximum value of the dielectric constant decreases. And a relatively large remnant polarization of 17.6 μC/cm² and 157 pC/N of d₃₃ has been obtained when x = 0.3.     

Phase-transformation-induced microstructure in lead-free ferroelectric ceramics based on (Bi0.5Na0.5)TiO3–BaTiO3–(Bi0.5K0.5)TiO3

Lead-free ferroelectric ceramics with a morphotropic phase boundary (MPB) composition 85.4% (Bi_0.5Na_0.5)TiO₃–2.6%BaTiO₃–12.0% (Bi_0.5K_0.5)TiO₃ (BNT-BT-BKT at a molar ratio of 85.4: 2.6: 12.0) doped with 0.8?mol% Nb₂O₅ were studied for their crystalline phases and microstructure. The crystalline phases were identified using X-ray diffractometry (XRD) with the contents determined using the Rietveld refinement technique. The phase-transformation-induced microstructure was analyzed using transmission electron microscopy (TEM) and the crystal symmetries were determined using the convergent-beam electron diffraction (CBED) technique. Samples sintered at 1200°C contain a mixture of cubic (C-), tetragonal (T-) and rhombohedral (R-) phases at a ratio of C/T/R?=?56.6: 28.4: 15.0?wt%. Two types of grains are produced: one characterized by a featureless contrast consisting of nano-scale T-domains dispersed in a C-phase matrix; the other a core-shell structure with a shell containing twin and anti-phase-boundary (APB) domains coexisting with a (C?+?T)-phase mixture core. The T- and R-twin boundaries are determined to {111}_T and {110}_R, respectively, and the fault vector for T-APB to R?=?1/2?110]_T. The characteristic microstructure is discussed in terms of the reduction in the point group symmetry and changes in the unit cell volume or the Bravais lattice upon phase transformation among the C-, T- and R-phases. The twin and the APB domains are induced and explained.     

Fe0.5Cu0.5BaSrYCu2Oy化合物的结构和超导电性研究

实验采用常压和高压分别制备出含铁的FexCu1-xBaSrYCu2Oy（x= 0～1）系列化合物，本文主要研究x=0.5时样品的结构和超导电性.测量结果显示，高压合成的样品均具有超导电性，对于x=0.5的样品超导转变温度Tc(onset)～57K， Tc(0)～40K，而常压合成的样品当Fe含量x>0.3时均不超导.为此，我们利用透射电子显微镜（TEM）研究了该体系的微观结构特性，并通过电子能量损失谱(EELS)揭示出高压合成导致样品中载流子浓度明显高于常压样品，证明样品制备过程中高压有利于超导电性的形成.同时对高压样品中的缺陷和局域晶体结构畸变进行了深入分析.     

SryBa1－yFCl0.5Br0.5:Sm2+在光谱

本文对无机光谱烧孔系列材料SryBa1－yFCl0.5Br0.5:Sm2+中不同组份的样品(y=0,0.25.0.5,0.75.1.00)4f5d能带的激发光谱、不同温度下5D2、5D1、5D0→7F0跃迁的荧光衰减进行了测量,研究了组份的变化对4f5d能带的位置,5D2、5D1、5D0→7F0跃迁的几率和烧孔效率的影响,并得出结论:在该系列材料中,随组份y的增加,4f5d带与5DJ能级更加接近,5D0→7F0的电子跃迁几率增大,烧孔效率提高。     

μ+SR study of Ising spin-glass Fe0.5Mn0.5TiO3

A typical Ising spin-glass Fe_0.5Mn_0.5TiO₃ has been investigated by ⁺ spin relaxation measurements. It is found that the local magnetic fields at the ⁺ stopping sites appear at a temperature twice as high asT _SG. The directional distribution of the local magnetic fields is nearly isotropic, indicating the existence of the transverse spin components. It is clearly demonstrated that the spins fluctuate belowT _SG and even at 4 K. Taking into account the results obtained by other methods, the main part of the fluctuations is inferred to be due to the transverse spin components and the fluctuation limes at 4 K are driven into a range between 10^–5 and 10^–7 s.     

Grain-Size Effect on the Dielectric Properties of Bi0.5Na0.5TiO3

We prepared bismuth sodium titanate (Bi0.5Na0.5TiO3)ultrafine powders by the sol-gel method.The dielctric properties of the pressed pellets and fired ceramics with different grain sizes as a function of tempernature at various frequencies were studied.With decreasing grain size,the dielecric anomaly around 200℃ increases,while the dielectric thermal hysteresis decreases,All the samples with grain sizes larger than 100nm show dielectric peaks at temperature of about 350℃.The very little change in Tm observed down to the critical size indicates that Bi0.5Na0.5TiO3 is an order-disorder system above 200℃,In addition,the dielectric peak becomes lower with decreasing grain size and the ferroelectric critical size of Bi0.5Nan0.5TiO3 was eventually determined to be about 100nm according to the disappearance of dielectric peak.