BNT-BT和BNT-BKT基无铅压电陶瓷研究进展

综述了Bi0.5Na0.5TiO3-BaTiO3系和Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3系无铅压电陶瓷的最新研究进展.总结了各种添加剂对这两种无铅压电陶瓷体系压电性能的影响机理和规律,介绍了当前以各种工艺对其微观结构和压电性能进行改进的研究成果,并展望了这两种无铅压电陶瓷体系的发展趋势.     

脉冲激光沉积Ba0.5Sr0.5TiO3、Pb0.5Ba0.5TiO3和Pb0.5Sr0.5TiO3薄膜及其介电性质

采用脉冲激光沉积法,在Pt／Ti／SiO2／Si基底上分剐制备厚度为350nm的Ba0.5Sr0.5TiO3(BST)、Pb0.5Ba0.5TiO3(PBT)和Pb0.5Sr0.5TiO3(PST)薄膜并研究了它们的介电性质。XRD显示,在相同的制备条件下三者具有不同的择优取向,PST具有(110)择优取向,PBT具有(111)择优取向,而BST则是混合取向。SEM显示三者样品表面均匀致密,颗粒尺寸大约在50nm至150nm之间。PST与BST、PBT相比有更高的介电常数,在频率为10kHz时,分别为874、334和355,而损耗都较低,分别为0．0378、0．0316和0．0423,同时PST漏电流也是最小的。测量薄膜的C-V特性扣铁电性能表明室温下BST呈现的是顺电相,PST和PBT则呈铁电相。本文也测量了薄膜在不同频率下的介电温度特性,BST、PBT和PST均表现出频率弥散现象,即随着频率的降低．居里温度降低而介电常数会升高。并测得BST和PST的居里温度分剐为-75和150℃。而PBT的居里温度在250℃以上。本文研究表明：与BST相比较,PBT的介电常数与之相近,漏电流较大;而PST具有高介电常数,较小的漏电流和较大的电容-电压调谐度,在相关半导体器件中的应用将有很大的潜力。     

溶胶-凝胶法制备Bi0.975La0.025Fe0.975Ni0.025O3铁电薄膜的结构及物理性能

采用溶胶-凝胶法在Pt/Ti/SiO_2/Si(111)衬底上制备了Bi_(0.975)La_(0.025)Fe_(0.975)Ni_(0.025)O_3(BLFNO)铁电薄膜。利用X射线衍射(XRD)、原子力显微镜(AFM)及其压电模式(PFM)对薄膜的晶体结构、表面形貌以及铁电畴结构进行了研究。研究发现,BLFNO为结晶良好的钙钛矿结构多晶薄膜,且薄膜表面颗粒生长均匀。PFM测试图显示铁电薄膜在自发极化下的铁电畴结构清晰,铁电电容器具有良好的铁电性能。应用铁电测试仪对Pt/BLFNO/Pt电容器进行测量,得到了饱和性良好的电滞回线。在828kV/cm的外加电场下,Pt/BLFNO/Pt电容器的剩余极化强度为74.3μC/cm~2,表明La、Ni的共掺杂没有明显抑制铁电电容器的剩余极化强度,铁电电容器具有良好的铁电性能。漏电流研究结果表明,La、Ni元素的共掺杂有效降低了薄膜的漏电流密度,在277.8kV/cm外加电场下漏电流密度在10-4 A/cm2量级,明显小于纯BFO薄膜的漏电流密度。正半支漏电流曲线满足SCLC导电机制,对于负半支曲线,当电场强度大于22.2kV/cm时,同样遵循SCLC导电机制;但是,当电场强度小于22.2kV/cm时,曲线斜率约为4.8,表明参与导电贡献的电子数较多,归因于极浅陷阱俘获的电子在外加电场作用下参与了导电行为。室温下磁滞回线测试结果表明BLFNO薄膜具有反铁磁性质。     

Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3无铅压电陶瓷的制备与性能

采用传统的干压成型法制备了Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3无铅压电陶瓷,研究了不同K0.5Bi0.5TiO3含量对Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3陶瓷的微观结构与电性能的影响规律.结果表明,Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3无铅压电陶瓷随K0.5Bi0.5TiO3含量增加,晶格常数增大,密度减小,晶粒尺寸减小,压电常数先增大后减小,介电常数增大,介电损耗增加,机械品质因数下降,而居里温度不断升高,在200℃附近存在由铁电相向反铁电相转变的一个相变点,组分为0.84 Na0.5Bi0.5TiO3-0.16 K0.5Bi0.5TiO3的陶瓷位于准同型相界附近,具有最佳的压电性能.     

Heat capacity, thermopower and magnetoresistance effects in multiferroic La0.5Bi0.5Mn0.5Fe0.5O3

We have carried out systematic investigations in perovskite multiferroic La_0.5Bi_0.5Mn_0.5Fe_0.5O₃ by means of X-ray diffraction, magnetisation, electrical resistivity, thermoelectric and heat capacity measurements. The magnetic behaviour of this composition is rather complex, though the magnetisation curve seems to be like a weak ferromagnetic material. However, there is no clear evidence of λ-anomaly in the heat capacity data down to 2 K, yet this behaviour corroborate the trends of semiconducting silicon below room temperature. The sensitivity of magnetic behaviour to the iron-manganese ratio is also demonstrated. In presence of an external field of 7 T, it exhibits a magnetoresistance of ?5 % at 130 K. The thermoelectric value increases linearly with decreasing temperature, and at room temperature the value is +85 μV/K, which is associated with the p-type polaronic conductivity.     

Na0.5 Bi0.5 TiO3-K0.5 Bi0.5 TiO3系铁电体的相变研究

研究了(Na1-xKx)0.5Bi0.5TiO3体系x分别为0、0.08、0.16和0.20时陶瓷不同频率下的介电温谱,发现材料为弛豫型铁电体,材料的介电谱在室温到500℃的温度范围内存在一个介电常数-温度"台阶",一个介电常数-温度峰和一个介电损耗-温度峰,通过分析陶瓷不同温度下的电滞回线验证陶瓷在升温过程中产生了铁电-反铁电-顺电相变,采用铁电体成分起伏理论和内电场理论解释了这类弛豫型铁电体相变的原因.     

Superconductivity in Layered CeO0.5F0.5BiS2

We report appearance of superconductivity in CeO_0.5F_0.5BiS₂. The bulk polycrystalline samples CeOBiS₂ and CeO_0.5F_0.5BiS₂ are synthesized by conventional solid state reaction route via vacuum encapsulation technique. Detailed structural analysis showed that the studied CeO_0.5F_0.5BiS₂ compound is crystallized in tetragonal P4/nmm space group with lattice parameters a=4.016(3) Å, c=13.604(2) Å. DC magnetization measurement (MT-curve) shows the ferromagnetic signal at the low temperature region. The superconductivity is established in CeO_0.5F_0.5BiS₂ at $T_{c}^{\mathrm{onset}}=2.5~\mbox{K}$ by electrical transport measurement. Under applied magnetic field, both T _c onset and T _c (ρ=0) decrease to lower temperatures and an upper critical field [H _c2(0)] above 1.2 Tesla is estimated. The results suggest coexistence of ferromagnetism and superconductivity for the CeO_0.5F_0.5BiS₂ sample.     

Positive delayed photoconductivity in double heterostructures Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As of the p-type

Positive delayed photoconductivity was observed for the first time in double p-type heterostructures Al_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5 As upon exposure to the radiation of a red light-emitting diode. In this state, the concentration and mobility of two-dimensional holes are increased 1.5 and 1.7 times, respectively, as compared to the initial dark values. The delayed photoconductivity can be explained by the presence of deep electron traps located above the Fermi level at the inverted heterointerface.     

Structure and electrical properties of Bi0.5Na0.5TiO3-Y0.5Na0.5TiO3-BaTiO3 lead-free piezoelectric ceramics

New (1 – x ? y)Bi_0.5Na_0.5TiO₃-xY_0.5Na_0.5TiO₃-yBaTiO₃ lead-free ceramics have been prepared by a conventional ceramic fabrication technique, and their structure and electrical properties have been studied. A morphotropic phase boundary (MPB) of rhombohedral and tetragonal phases is formed at 0.04 < y < 0.10. As compared to pure Bi_0.5Na_0.5TiO₃ ceramic, the partial substitutions of Y³⁺ for Bi³⁺ and Ba²⁺ for (Bi_0.5Na_0.5)²⁺ in the A-sites of Bi_0.5Na_0.5TiO₃ lower effectively the coercive field E _c and increase the remanent polarization P _r of the ceramics. Because of low E _c, large P _r and the MPB, the ceramics with x = 0–0.02 and y = 0.06 exhibit the optimum piezoelectric properties: d ₃₃ = 155–159 pC/N and k _p = 28.8–36.7%. The temperature dependences of dielectric properties of the ceramics show relaxor-like behaviors. The ferroelectric properties at different temperature suggest that the ceramics may contain both the polar and non-polar regions near/above T _d.     

Ellipsometric characterisation of ordered Ga0.5 In0.5 P

Abstract

The characterisation of ordered GaInP by room temperature ellipsometry is reported. Anisotropy effects were observed around the energy range of the E₁ interband transition and their evolution with the degree of order in the alloy has been studied. The spectra were analysed using a two phase model and the results obtained with a simple approximate treatment are compared with those of an exact anisotropic treatment.     

Gd2O3 doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 lead-free piezoelectric ceramics

Gd₂O₃ (0–0.8 wt.%)-doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state process. The effects of Gd₂O₃ on the microstructure, the dielectric, ferroelectric and piezoelectric properties were investigated. X-ray diffraction (XRD) data shows that Gd₂O₃ in an amount of 0.2–0.8 wt.% can diffuse into the lattice of BNKT18 ceramics and form a pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain size of BNKT18 ceramics decreases with the increase of Gd₂O₃ content; in addition, all the modified ceramics have a clear grain boundary and a uniformly distributed grain size. At room temperature, the ferroelectric and piezoelectric properties of the BNKT18 ceramics have been improved with the addition of Gd₂O₃, and the BNKT18 ceramics doped with 0.4 wt.% Gd₂O₃ have the highest piezoelectric constant (d₃₃ = 137 pC/N), highest relative dielectric constant (ε_r = 1023) and lower dissipation factor (tan δ = 0.044) at a frequency of 10 kHz. The BNKT18 ceramics doped with 0.2 wt.% Gd₂O₃ have the highest planar coupling factor (k_p = 0.2463).     

La3+掺杂Co0.5Ni0.5(Fe0.5Cr0.5)2O4尖晶石红外辐射材料的研究

用固相合成法制备La3+掺杂Co0.5Ni0.5(Fe0.5 Cr0.5)2O4尖晶石体系红外辐射材料,并通过DTA-TG、XRD和IRE-2型红外辐射测试等方法研究了材料的结构特征与红外辐射性能的关系,结果表明:随着La3+含量的增加,La3+以不同的形式进入Co0.5Ni0.5(Fe0.5 Cr0.5)2O4体系中,当La2O3掺杂浓度为5%(质量分数)时,样品的法向全波段辐射率达到0.91.     

粉末溶胶法制备Pb0.90La0.10Ti0.975O30-3型厚膜的研究

使用溶胶-凝胶法制备了Pb0.90La0.10Ti0.975O3(简称为PLT-1O)粉体，使用XRD及日本SALD-2001型激光散射颗粒度分析仪对粉体进行了分析，结果表明PLT-1O粉体呈钙钛矿结构，一次颗粒细，颗粒尺寸随退火温度的升高而增大。将粉体分散在溶胶中，并采用粉末溶胶法制备了PLT-1O厚膜。利用XRD和SEM对厚膜进行了分析。实验结果表明，适当调控制备工艺技术，利用粉末溶胶法可望制备出符合要求的铁电“厚膜”。     

High dielectric constant ceramics in the PbSc0.5Ta0.5O3-PbZrO3 and PbSc0.5Ta0.5O3-PbTiO3 systems

The properties of (1-x) PbSc_0.5Ta_0.5O₃-(x) PbZrO₃ ceramics (0.075 <x < 0.2), have been investigated using three different mixed oxide preparation routes. These were (i) a single-stage calcination (at 900°C) between lead, scandium, tantalum and zirconium oxides, (ii) the reaction between single phase PbSc_0.5Ta_0.5O₃ and PbZrO₃ powders (also at 900°C), and (iii) the formation of zirconium-modified scandium tantalate (via a high-temperature prereaction stage) prior to calcination with lead oxide. It was found that this third preparation route results in transparent, 100% dense, single-phase perovskite ceramics which exhibit particularly sharp first-order ferroelectric to paraelectric phase transitions. Material with a maximum relative permittivity of 36 × 103 at 64°C, and a dielectric loss of 7.5 × 10^–4, was obtained for anx value of 0.125. Results are compared with those for ceramics in a similar range of compositions in the (1-x) PbSc_0.5Ta_0.5O₃-(x)PbTiO₃ system; these were prepared using only one of the above routes, and involved calcining PbSc_0.5Ta_0.5O₃ with PbTiO₃ powder.     

Zr4+B位置换对(Pb0.5Ca0.5)(Fe(0.5)Nb0.5)O3

研究了Zr4+离子B位置换改性对(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷微波介电性能.实验结果表明,(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3(PCFNZ)陶瓷样品呈现单一斜方钙钛矿相结构.随Zr(4+)离子的置换量增加,PCFNZ陶瓷体系的Qr值和晶粒尺寸逐渐减小;介电常数εr随着置换量增加...     

Magnetocaloric Effect of Perovskite Eu0.5Sr0.5CoO3

Magnetocaloric properties of the Eu_0.5Sr_0.5CoO₃ system near a phase transition from a ferromagnetic to a paramagnetic state are investigated. It is shown that the magnetic entropy change (ΔS _M ) peak spanning over a broad range of temperature leads to a remarkably wide working temperature region, yielding a significant performance in terms of refrigerant efficiency. Moreover, ΔS _M distribution is very uniform, which is desirable for Ericsson-cycle magnetic refrigerator. Eu_0.5Sr_0.5CoO₃ can be used as a working material of an apparatus based on the active magnetic regenerator cycle that cools hydrogen gas.