Ca2+和Mn2+共掺杂Ba1-xSrxTiO3固溶体的制备及其电学性能 研究

利用溶胶-凝胶法制备了Ca2 和Mn2 共掺杂Ba1-xSrxTiO3 (BST)固溶体．采用TG-DTA热分析、XRD衍射和TEM透射电镜对其进行了表征,并研究了热处理温度和外加直流偏压对其电学性能的影响．XRD显示,Ca2 和Mn2 共掺杂没有改变BST的结构．TEM照片揭示了热处理温度对其形貌的影响．阻温特性曲线显示,在低频时它显示正温度系数效应(PTC),在其它频率则显示负温度系数效应(NTC)．电阻与电压关系显示,低频时它呈现电阻特性,而高频时则显示容抗特性．这些结果说明,掺杂能调节BST材料的电学性能;这些现象可以用晶界电阻效应,Heywang模型和离子极化理论来解释．     

高居里温度PTCR半导体陶瓷及其制备

具有高铁电居里温度 Tc的(Ba1-xPbx)TiO3系材料是正温度系数热敏电阻(PTCR)陶瓷.它是一种理想的高温、恒温发热体材料.可用它制作中、小型加热、烘烤设备(如暖风机、自动恒温电烙铁、电热杯、电吹风、恒温电烫斗等各种加热器件),还可用它制成过热和过流保护元件以及控温元件.用该材料制成的器件,升温迅速,能自动恒温,耗电少,寿命长. PTCR陶瓷属于多晶铁电半导体.该陶瓷的阻温特性曲线如图1所示.当开始在陶瓷体上施加工作电压时,温度低于 Tmin,陶瓷体呈负电阻温度系数特性,随着温度的上升,电阻率下降,电流增大.由于ρmin很低,故有一大…     

Y替代La2/3Ca1/3MnO3体系的结构与输运行为

系统研究了(La1-xYx)2/3Ca1/3MnO3(0.0≤x≤0.3)体系的结构和输运行为.结果表明，实验样品具有很好的单相结构，随Y掺杂浓度的增加，金属—绝缘体（M—I）转变温度T-MI向低温区移动，对应的峰值电阻率ρp升高，对x=0.3样品，较未替代样品（x=0.0）增幅达8个数量级.在外加磁场下，材料表现出很强的磁电阻效应.同时，从实验结果出发，直接给出了输运特性与晶体结构之间的关联，并从双交换模型和可变程跃迁理论出发，对实验结果进行了初步讨论. 关键词： La2/3Ca1/3MnO3锰氧化物 Y替代 晶体结构 输运行为     

Pb(Sc_(1/2)Nb_(1/2))O_3中有序-无序转变和铁电相变的Raman光谱研究

采用wolframite前驱物法制备了Pb(Sc1/2Nb1/2)O3陶瓷。通过调节陶瓷烧结工艺,获得了三种具有不同B位离子有序度的PSN陶瓷。测量了三种陶瓷样品在室温至160°C范围内的Raman光谱随温度变化。结果表明,随着温度的升高,三种不同B位有序度的陶瓷样品中,Raman光谱中位于530 cm-1的F2g模的峰位和半峰宽分别在100°C,85°C和80°C发生了突变,表明陶瓷分别在100°C,85°C和80°C三个温度点发生了铁电-顺电相变。上述结论得到了介电温度谱测量数据的支持。     

KNb_(1-x)Mg_xO_(3-δ)的高温高压合成及输运性质研究

采用高温高压法制备了KNb1-xMgxO3 -δ(x =0 .0～ 0 .3)氧离子导电材料 ,使用XRD、TG-DTA及交流复阻抗谱对样品的结构和离子导电性进行了表征。实验结果表明 ,高压降低了合成温度 ,合成的KNb1-xMgxO3 -δ系列固溶体与其母体KNbO3 一样都为正交钙钛矿结构 ,晶胞参数随掺杂量的增加而略微增大。固溶体KNb1-xMgxO3 -δ具有离子导电特征 ,通过拟合阻抗谱数据获得了该材料晶粒电导、晶界电导和体电导率与温度的关系。样品的晶界电阻较高 ,晶界效应十分明显 ,离子跳跃传导可能在其输运机制中占据主导地位。在x =0 .1附近 ,电导率达到最大值 ,70 0℃时为 1.2× 10 - 3 S·cm- 1。     

Pr0.7Ca0.3MnO3陶瓷晶界势垒的交流特性

采用固相烧结方法制备了Pr1-xCaxMnO3(x=0.3)钙态矿结构锰氧化物陶瓷样品,对其在磁场和电场下的直、交流输运性质做了系统研究.通过测量加磁场和零场下的Ⅰ-Ⅴ曲线,得到其居里温度为150K,与VSM测试结果一致.通过测量加磁场与零场下交流的阻抗频谱,发现加磁场后样品的晶界电阻明显减小,而晶粒电阻几乎保持不变,表明Pr1-xCaxMnO3陶瓷多晶样品的CMR效应源于样品的晶界.为确定晶界处的势垒高度,测量了样品在不同频率下的阻抗温谱,根据Arrhenius定律拟合得出势垒高度为117 meV,与用直流R-T数据拟合得出的激活能一致.     

CaCu3Ti4O12陶瓷的微观结构及直流导电特性

采用传统固相反应法制备了CaCu₃Ti₄O₁₂陶瓷.XRD证实其CaCu₃Ti₄O₁₂相；SEM观察到明显的晶粒晶界结构，晶界区亦由小晶粒构成；结合EDS结果，判定晶界区小晶粒为CuO.在较宽的温度范围内，CaCu₃Ti₄O₁₂陶瓷的介电常数保持在10⁵左右；当频率为10³ Hz温度小于150 K时，介电常数迅速下降.在173—373 K温度范围内，通过其I-V特性，得到CaCu₃Ti₄O₁₂陶瓷直流电导随温度的变化：直流电导与温度的关系可分为三部分，对应的活化能分别为0.681 eV，0.155 eV和0.009 eV，这与CuO陶瓷直流电导活化能一致.可以认为晶界区的CuO小晶粒在CaCu₃Ti₄O₁₂陶瓷的直流电导中占主导，这为解释CaCu₃Ti₄O₁₂陶瓷反常的介电性能提供了新的思路. 关键词： 3Ti₄O₁₂')" href="#">CaCu₃Ti₄O₁₂ 微观结构 直流电导 介电特性     

Al2O3-Y2O3-ZrO2三相复合陶瓷的介电谱研究

采用传统的固相反应法,在1400–1500 ℃下烧结,制备得到Al₂O₃-Y₂O₃-ZrO₂三相复合陶瓷.样品的结构、形貌和电性能分别用X射线衍射(XRD)、扫描电子显微镜(SEM)及介电谱表征.XRD表明此三相复合体系无其他杂相,加入Y₂O₃及ZrO₂后使得Al₂O₃成瓷温度降低;SEM表明此体系晶粒直径为200–500 nm,并且样品随烧结温度的升高而变得更加致密,晶界更加清晰;介电损耗谱中出现峰值弛豫现象,根据Cole-Cole复阻抗谱得出其为非德拜弛豫. 关键词： 2O₃-Y₂O₃-ZrO₂三相陶瓷')" href="#">Al₂O₃-Y₂O₃-ZrO₂三相陶瓷 介电弛豫 阻抗谱 热导率     

非化学计量和掺杂对(Na_(1/2)Bi_(1/2))_(0.92)Ba_(0.08)TiO_3陶瓷电性能的影响

研究了非化学计量和掺杂对无铅压电陶瓷 (Na1 2 Bi1 2 ) 0 .92 Ba0 .0 8TiO3的压电性能及去极化温度的影响 .研究发现A位非化学计量可以提高陶瓷的压电性能 ;B位掺杂对材料电学性能的影响规律类似于Pb(Ti,Zr)O3系压电陶瓷的相关规律 ;由于非化学计量和掺杂会影响到A位离子对B位离子与氧离子形成的BO6 八面体的耦合作用 ,影响到畴的稳定性 ,从而影响到 (Na1 2 Bi1 2 ) 0 .92 Ba0 .0 8TiO3陶瓷的去极化温度 ;所研究的陶瓷样品的去极化温度越低 ,压电系数越高 .     

Bi0.5Ba0.5FeO3 陶瓷的电性能及阻抗分析

以传统的固相反应法制备了Bi_0.5Ba_0.5FeO₃陶瓷,并采用X射线衍射仪、扫描电子显微镜、直流阻温测试仪和交流阻抗分析仪测试了Bi_0.5Ba_0.5FeO₃陶瓷的微结构和电性能.分析结果表明:Bi_0.5Ba_0.5FeO₃陶瓷具有立方钙钛矿结构,颗粒尺寸约1.0 μm;在16—280 ℃范围内,Bi_0.5Ba_0.5FeO₃陶瓷表现出明显的负温度系数热敏效应,其热敏常数、活化能分别为6490 K及0.558 eV;介电温谱揭示,在280 ℃下Bi_0.5Ba_0.5FeO₃陶瓷材料没有出现相变行为.对于交流阻抗谱,采用3个串联的RQ(R与Q为并联)等效部件来拟合分析,拟合结果表明拟合数据与实验数据高度匹配,且这3个等效部件分别代表晶界、晶粒和晶壳的贡献.3个部件中,晶粒对陶瓷电阻阻值的影响最大,晶壳贡献次之,晶界最小,且3个部件电阻值都显示出负温度系数效应.在25—115 ℃范围内,电学模量虚部峰频与阻抗虚部峰频始终不匹配,意味着Bi_0.5Ba_0.5FeO₃陶瓷体内部一直表现出局域导电机理. 关键词： 0.5Ba_0.5FeO₃陶瓷')" href="#">Bi_0.5Ba_0.5FeO₃陶瓷 电性能 阻抗分析     

boldmath Characterization of the BaBiO3-doped BaTiO3 positive temperature coefficient of a resistivity ceramic using impedance spectroscopy with Tc=155℃

BaBiO₃-doped BaTiO₃ (BB-BT) ceramic, as a candidate for lead-free positive temperature coefficient of resistivity (PTCR) materials with a higher Curie temperature, has been synthesized in air by a conventional sintering technique. The temperature dependence of resistivity shows that the phase transition of the PTC thermistor ceramic occurs at the Curie temperature, T_c=155 ℃, which is higher than that of BaTiO₃ ( ≤ 130 ℃). Analysis of ac impedance data using complex impedance spectroscopy gives the alternate current (AC) resistance of the PTCR ceramic. By additional use of the complex electric modulus formalism to analyse the same data, the inhomogeneous nature of the ceramic may be unveiled. The impedance spectra reveal that the grain resistance of the BB-BT sample is slightly influenced by the increase of temperature, indicating that the increase in overall resistivity is entirely due to a grain-boundary effect. Based on the dependence of the extent to which the peaks of the imaginary part of electric modulus and impedance are matched on frequency, the conduction mechanism is also discussed for a BB-BT ceramic system.     

Dielectric and impedance measurements on (1−x)Ba(Fe1/2Ta1/2)O3-xBa(Zn1/3Ta2/3)O3 ceramics

In this work, ((1−x)Ba(Fe_1/2Ta_1/2)O₃-xBa(Zn_1/3Ta_2/3)O₃), ((1−x)BFT-xBZT) ceramics with x = 0.00–0.12 were synthesized by the solid–state reaction method. X-ray diffraction data revealed that both the powders and ceramics were of a pure-phase cubic perovskite structure. All ceramics showed large dielectric constants. For the x = 0.12 sample, a very high dielectric constant (>20,600) was observed. A lowering in the dielectric loss compared to pure BFT ceramics was observed with the BZT addition. The impedance measurements indicated that BZT has a strong effect on the bulk grain and grain boundary resistance of BFT ceramics. These results are in agreement with the measured dielectric properties. Based on dielectric and impedance results, (1−x)BFT-xBZT ceramics could be of great interest for high performance dielectric materials applications due their giant dielectric constant behavior.     

The room-temperature ferromagnetism of defect-rich ZnMgO semiconductor thin films

The positive temperature coefficient of resistance (PTCR) characteristics of Na₂Ti₆O₁₃ (NT)-doped 0.94BaTiO₃–0.06(Bi_0.5Na_0.5)TiO₃ (BBNT) ceramics were investigated in order to evaluate the effect of NT as a new additive for lead-free PTCR thermistor application. The BBNT ceramic sintered at 1325°C exhibited a relatively high Curie temperature (T _C ) of 158°C while its PTCR characteristic was not satisfactory for thermistor application. However, doping with NT significantly influenced the PTCR behavior of BBNT ceramic. It is considered that NT was responsible for grain growth of the BBNT by forming a liquid phase during sintering due to its low melting temperature of 1300°C. The grain growth resulted in the enhanced PTCR characteristics of BBNT ceramic. In particular, 0.1 mol% NT doped BBNT ceramic exhibited excellent PTCR performance of low resistivity at room temperature (1.6×10² Ω cm), resistivity increase near T _C (1.28×10⁴) and high T _C of 158°C, suitable for lead-free PTCR thermistor application.     

Crystal structure and magnetic properties of Nd（Mn1-xFex）2Si2 compounds

X-ray powder diffraction,resistivity and magnetization studies have been performed on polycrystalline Nd(FexMn1-x)2Si2 (0 ≤ x ≤ 1) compounds which crystallize in a ThCr2Si2-type structure with the space group I4/mmm.The field-cooled temperature dependence of the magnetization curves shows that,at low temperatures,NdFe2Si2 is antiferromagnetic,while the other compounds show ferromagnetic behaviour.The substitution of Fe for Mn leads to a decrease in lattice parameters a,c and unit-cell volume V .The Curie temperature of the compounds first increases,reaches a maximum around x = 0.7,then decreases with Fe content.However,the saturation magnetization decreases monotonically with increasing Fe content.This Fe concentration dependent magnetization of Nd(FexMn1-x)2Si2 compounds can be well explained by taking into account the complex effect on magnetic properties due to the substitution of Mn by Fe.The temperature’s square dependence on electrical resistivity indicates that the curve of Nd(Fe0.6Mn0.4)2Si2 has a quasi-linear character above its Curie temperature,which is typical of simple metals.     

Unusual piezoresponse behavior across the grain boundary of PbMg1/3Nb2/3O3-0.33PbTiO3 thin films

Ferroelectric PbMg_1/3Nb_2/3O₃-0.33PbTiO₃ (PMN-0.33PT) polycrystalline thin film near MPB was grown on Ir with LaNiO₃ buffer layer by pulsed laser deposition technology. Piezoresponse force microscopy (PFM) was employed to investigate the role of grain boundary on the domains formation and their local physical properties in PMN-PT thin film. Unusual piezoresponse behaviors were firstly observed across the grain boundary of PMN-PT thin film via PFM. Such abnormal phenomenon is ascribed to the structural incompatibility-induced local stress across the grain boundary, which gives a deep influence on the local imprint behavior of PMN-PT thin film.     

Influences of Bi2O3 on microstructure and magnetic properties of MnZn ferrite

MnZn ferrites were prepared by conventional oxide ceramic process. The effects of Bi₂O₃ on microstructure and magnetic properties of MnZn ferrites were investigated by means of characterizing the fracture surface micrograph, composition of grain boundary, magnetic properties and density by scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDS), B-H analyzer and Archimedes method, respectively. The results indicate that Bi₂O₃ mainly segregates and concentrates in the grain boundary regions, promotes solid-state reaction and grain growth, reduces porosity and enhances density. Optimum addition of Bi₂O₃ increases the permeability and saturation magnetic induction, meanwhile ensures the well frequency stability of permeability.     

Structure and dielectric studies of nano-composite Fe2O3: BaTiO3 prepared by sol-gel method

Nano-structure pure barium titanate (BaTiO₃) and that was doped with iron oxide (Fe₂O₃), have been prepared by sol-gel method, using barium acetate (Ba(Ac)₂) and titanium butoxide (Ti(C₄H₉O)₄), as precursors. The as-grown prepared samples by sol-gel technique were found to be amorphous, which crystallized to the tetragonal phase after synthesized at 750 °C in air for 1 h as detected from the XRD patterns. The XRD data were confirmed by transmission electron microscope (TEM). The dielectric properties namely; dielectric constant (ε′) and loss tangent (tan δ) in the frequency range between 42 Hz and 1 MHz, at range of temperature 25-250 °C were investigated. The temperature dependence of ε′ and tan δ for the undoped and doped materials, at 1 kHz, was also investigated. As a result, tan δ increased rapidly with decreasing temperature below 125 °C (Curie temperature) while above this temperature, tan δ shows temperature independent. As a result, below and above Curie temperature, ferroelectric phase and paraelectric phase of BaTiO₃ can be obtained, respectively.     

Complex impedance spectroscopic studies of Ba(Pr1/2Ta1/2)O3 ceramic

The polycrystalline sample of Ba(Pr_1/2Ta_1/2)O₃ was prepared by a high-temperature solid-state reaction technique. The crystal symmetry, space group and unit cell dimensions were derived from the experimental results using FullProf software. XRD analysis of the compound indicated the formation of a single-phase tetragonal structure with the space group P4/mmm (1 2 3). Impedance and electric modulus analysis were used as tools to analyze the electrical behavior of the sample as a function of frequency at different temperatures. The impedance analysis of the compound indicated a typical negative temperature coefficient of resistance behavior, and dielectric relaxation was found to be of non-Debye type. The frequency dependent maximum of the imaginary part of the electric modulus follows the Arrhenius law with activation energy of 0.15 eV. The ac conductivity data obeys double power law.     

基于Si掺杂Sb2Te3薄膜的相变存储器研究

采用磁控三靶(Si，Sb及Te)共溅射法制备了Si掺杂Sb₂Te₃薄膜，作为对比，制备了Ge₂Sb₂Te₅和Sb₂Te₃薄膜，并且采用微加工工艺制备了单元尺寸为10μm×10μm的存储器件原型来研究器件性能.研究表明，Si掺杂提高了Sb₂Te₃薄膜的晶化温度以及薄膜的晶态和非晶态电阻率，使得其非晶态与晶态电阻率之比达到10⁶，提高了器件的电阻开/关比；同Ge₂Sb₂Te₅薄膜相比，16at% Si掺杂Sb₂Te₃薄膜具有较低的熔点和更高的晶态电阻率，这有利于降低器件的RESET电流.研究还表明，采用16at% Si掺杂Sb₂Te₃薄膜作为存储介质的存储器器件原型具有记忆开关特性，可以在脉高3V、脉宽500ns的电脉冲下实现SET操作，在脉高4V、脉宽20ns的电脉冲下实现RESET操作，并能实现反复写/擦，而采用Ge₂Sb₂Te₅薄膜的相同结构的器件不能实现RESET操作. 关键词： 相变存储器 硫系化合物 2Te₃薄膜')" href="#">Si掺杂Sb₂Te₃薄膜 SET/RESET转变