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1.
采用传统固相法制备了Ba0.6Sr0.4TiO3(BST)和BaZr< sub>xTi1-xO3(x=0.25,0.3,0.35,0.4)(BZT)陶瓷 ,并对其在直流偏置电场下的介电常数非线性行为进行了系统、详细的研究.结果表明,基 于Devonshire的宏观相变理论(phenomenological theory)提出的公式εr(app) εr(0)=1[1+αε3r(0)E2 ]1/3和ε(E)=ε1-ε2E2+ε3 sub>E4,均可定量地解释BST体系顺电相的介电常数非线性行为,其中εr (app)表示材料在电场下的介电常数,εr(0)表示不加电场即静态下材料 的介电常数,α是非谐性因子,E表示电场强度,ε(E)表示材料在电场下的介电常数,ε1,ε2,ε3分别表示线性、非线性和高阶介电常数. 而对于处于铁电相和居里温度附近的BST体系,则需要考虑铁电畴对介电常数非线性的贡献 ,这种贡献随着外加直流偏置电场强度的增大逐步减小.对于弛豫铁电体BZT体系,即使处于 顺电相,也必须考虑由极性微区的冻结与合并引起的介电常数的下降,极性微区对介电常数 非线性的贡献随着电场强度和温度的上升而有所下降.
关键词:
BST
xTi1-xO3')" href="#">BaZrxTi1-xO3
可调性
介电 常数非线性
直流偏置电场 相似文献
2.
用全电势线性缀加平面波法(FLAPW)计算了KTa0.5Nb0.5O3四方相和立方相 的光学特性,即介电函数虚部ε2(ω)、光学吸收系数I(ω)和反射率R(ω). 在四方相,介电虚部沿a,b轴,在3,7和23eV附近,分别有三个介电峰.沿c轴的三个介电峰分别位于4,8和23eV.其中4eV附近的介电峰非常尖锐而且高.从8至18eV,沿a,b ,c轴三个方向都有许多低的介电峰.通过对两相光学特性的对比分析发现铁电相KTa0.5Nb0.5O3具有更强的各向异性.
关键词:
平面波法计算
光学常量和参数
铁电体 相似文献
3.
按照叠加模型与EPR零场分裂参量的三阶微扰理论,建立了KCdF3:Cr3+晶体EPR零场分裂参量与四角对称Cr3+-Cd2+缺陷中心局域结构之间的定量关系.证实Cd2+空位与晶格畸变的存在,我们获得:围绕Cr3+离子的六个F-配体分别向中心Cr3+移动Δ1=0.00294nm,Δ2=0.0010nm,Δ3=0.0028nm (参见图2).EPR零场分裂参量与实验一致表明:Cd2+空位与晶格畸变的假设是合理的.尽管四角晶场主要来自Cd2+空位,但晶格畸变的贡献不可忽略. 相似文献
4.
通过sol-gel法在Si (111) 基片上分别制备了LaNiO3(LNO)底电极和LaNiO3/La0.3Sr0.7TiO3 (LNO/LSTO)底电极.然后采用sol-gel 方法,在两种衬底上分别制备了Pb (Zr0.5Ti0.5)O3 (PZT)铁电薄膜.XRD分析表明,两种PZT薄膜均具有钙钛矿结构,且在LNO底电极上的PZT薄膜呈(100) 择优取向,而在LNO/LSTO底电极上的PZT薄膜呈随机取向.铁电性能测试表明,相对LNO衬底上制备的PZT薄膜,在LNO/LSTO底电极上制备的PZT薄膜的剩余极化强度得到了有效的增强,同时矫顽场也增大.介电常数和漏电流的测试表明,LNO/LSTO底电极上制备的PZT薄膜具有大的介电常数和漏电流.
关键词:
PZT薄膜
铁电性
漏电流
0.3Sr0.7TiO3')" href="#">La0.3Sr0.7TiO3 相似文献
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采用改进的溶胶-凝胶方法在单晶Si(100)衬底上制备了介电性能优异的(Ba0.7Sr0.3)TiO3/LaNiO3异质薄膜.实验发现,在750 ℃下 、O2气氛中晶化的LaNiO3薄膜的电阻率最小.C-V与I-V特性测量表明(Ba0.7Sr0.3)TiO3薄膜具有优异的介电性能,在频率为50kHz、零偏压下的相对介电常数εr>300,偏压为6V时漏电流密度JL<1.2×10-6A/cm2.
关键词:
xSr1-x)TiO3铁电薄膜')" href="#">(BaxSr1-x)TiO3铁电薄膜
3底电极')" href="#">LaNiO3底电极
溶胶-凝胶法 相似文献
7.
郑永真 《核聚变与等离子体物理》2005,25(3):203-206
使用一维数值模型, 推断了逃逸能量εr与逃逸约束时间τr的关系。模拟结果给出能量εr 和放电参数的定标律。在HL- 1M 装置中不同实验条件下测量了硬X 射线谱, 研究了逃逸电子能量 εr模拟的定标律, 并推导出HL- 1M 装置放电的逃逸电子的约束时间与逃逸电子扩散系数。 相似文献
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采用电滞回线方法和偏置直流电场中叠加小交变电场方法研究了锆钛酸铅反铁电陶瓷材料在强电场作用下的介电行为.测量结果显示,锆钛酸铅反铁电材料的介电常数随外加电场强度呈非线性变化,在反铁电 铁电转变的电场区间形成介电峰.表征极化强度随电场强度变化率的微分介电常数εd峰值出现在反铁电 铁电转换电场强度处,最高达到41000.随着偏置电场增加反铁电向铁电体转变过程中,小信号介电常数εc减小;在电场降低铁电回复成反铁电过程中,小信号介电常数εc增大,小信号介电常数εc峰先于微分介电常数εd峰出现.根据电场作用下反铁电
关键词:
锆钛酸铅反铁电陶瓷
介电行为
强电场条件 相似文献
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G. I. Ovchinnikova A. P. Eremeev N. V. Belugina R. V. Gainutdinov E. S. Ivanova A. L. Tolstikhina 《Physics of Wave Phenomena》2017,25(3):231-237
Temperature dynamics of the dielectric spectra and domain structure in the triglycine sulfate (TGS) hydrogen-containing ferroelectric under heating and cooling has been studied using the dielectric spectroscopy and atomic-force microscopy methods. The dielectric spectra are analyzed by the temperature-frequency dependences of the losses ε″ and by the temperature behavior of the maximum losses ε″max in the dispersion region at frequencies ranging from 102 to 106 Hz. A dynamic conductivity model is proposed for calculating temperature dependences of losses ε″max. The domain structure dynamics during the heating and cooling of the TGS crystal near the phase transition is studied using the in situ piezoresponse force microscopy. It is experimentally and theoretically shown that the relaxation dispersion is governed by the binding of strongly correlated dipoles with the main lattice that serves as a thermostat. 相似文献
12.
Mehmet S. Bozgeyik 《Chinese Journal of Physics (Taipei)》2018,56(1):40-45
Novel strontium bismuth tantalate (Sr0.8Bi2.2Ta2O9 (SBT)) modified with 3 and 5 mol% ratio barium silicate (Ba2SiO4) thin films were grown on Pt(100?nm)/Ti(50?nm)/SiO2/Si(100) substrates by spin coating technique. The influence of barium silicate doping in SBT was studied from the view point of changing dielectric and ferroelectric properties like dielectric constant (εr) and remnant polarization (Pr). Well crystallized thin films showed convenient ferroelectric properties with comparatively lower Pr in the range between 1.52 and 0.44 µC/cm2 and smaller εr value of 163. Thus, with such reduced values of Pr and εr barium silicate modified SBT offers a useful potential to be used in Ferroelectric Field Effect Transistor (FeFET) type (1T-type) Ferroelectric Random Access Memories (FeRAMs) upon improving insulation properties. 相似文献
13.
Abstract A two-sublattice compressible pseudospin model has been constructed to describe the behaviour of the spontaneous polarisation of PMACB in the temperature region comprising the ferroelectric phase transition (T=307K) and the isomorphous anomaly (T= 180 K). A strong coupling of pseudospins with a “pancake” strain ?(2ε33 ? ε11 - ε22) /3 resulting from the comparison of the model with the experimental spontaneous polarisation agrees with the existing data on the dielectric susceptibility, and on the specific heat. The ferroelectric phase transition then turns out to be close to a tricritical point. The numerical values of the parameters of the model show how the ferroelastic phase transition (T=260K) can occur in this crystal without any discernible effect on the specific heat and on the dielectric susceptibility. 相似文献
14.
E. D. Politova N. V. Golubko G. M. Kaleva A. V. Mosunov N. V. Sadovskaya D. A. Bel’kova S. Yu. Stefanovich 《Physics of the Solid State》2018,60(3):428-432
The phase formation, specific features, and the dielectric properties of the ceramics of compositions from the region of morphotropic interface in the (Na0.5Bi0.5)TiO3–BaTiO3 system modified by Bi(Mg0.5Ti0.5)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 Tm ~ 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(Mg0.5Ti0.5)O3 favor a decrease in the electrical conductivity and dielectric losses of the samples, and the relative dielectric permittivity at room temperature εrt is retained quite high, achieving the highest values εrt = 1080–1350 in the ceramics modified with KCl. 相似文献
15.
The dependence of loss tangent (tanδ) and relative permittivity (εr) on temperature and frequency has been reported for Na2-XKXTi3O7 (with X=0.2, 0.3, 0.4) ceramics. The losses are characteristic of dipole mechanism and electrical conduction. The peaks of εr at high temperature indicate a possible ferroelectric phase transition for all three compositions. The results of a.c. conductivity studies on the same samples have also been reported. The corresponding ln(σT) versus 1000/T plots have been divided into five regions namely I, II, III, IV and V. The various conduction mechanisms in the different regions have been stressed. Furthermore, the log(σ) versus frequency plots for all the above samples reveal that the electronic hopping (polaron) conduction, which diminishes with the rise in temperature, is dominant in the lower temperature region. The interlayer ionic conduction seems to play a major role in conduction towards higher temperature. 相似文献
16.
用时域和频域方法研究了(Ba1-xSrx)TiO3陶瓷的极性相变.类似于单晶的铁电相变所观察到的晶格软化,屏蔽电荷激发和畴运动讯号外,在陶瓷中还出现空间电荷运动的强讯号.空间电荷和电畴属于凝聚态物质的高级结构,它提供慢极化效应.慢效应使频域测量结果不能得到确定值.从统计观点给出高级结构的历史记忆效应对频域测量结果的影响;解释了频域介电常量的倒数在一级结构的转变中发生线性软化,而在高级结构的转变中发生抛物型软化.
关键词: 相似文献
17.
Using an atomistic shell model we study the temperature dependence of the ferroelectric properties of BaTiO3 under biaxial compressive strain applicable to growth on perovskites substrate. Molecular dynamics simulations show a “r→c→p” sequence of phase transitions when temperature is increased, and the absence of an “ac phase”. The first-order paraelectric-to-ferroelectric phase transition presents in bulk changes to a second-order one as a consequence of the in-plane constraint imposed by the mechanical boundary conditions. From the tetragonal ferroelectric c phase, the transition takes place in a finite range of temperature where the lattice parameter normal to the plane keeps approximately constant until Tc is reached. Analysis of the local polarization behavior reveals an order–disorder dynamics as the dominant mechanism of the transition. 相似文献
18.
An ultracryostat and multidecameter were used to determine the temperature dependence of the dielectric constant ?′ and dielectric loss ?″ over a wide range of frequencies of single crystals and polycrystalline samples of (NH4)2SO4 in the region of the low temperature phase transition. A sharp increase was observed in the values of ?′ and ?″ at about ?50°C. In addition, a dielectric dispersion was detected and found to be more pronounced in the high temperature phase. This dispersion was attributed to piezoelectric resonance. The observed sudden increase in the values of the dielectric constant and dielectric loss below ? 50°C was attributed to the ferroelectric nature of the low temperature phase of (NH4)2SO4.A DTA thermogram showed a sharp peak at ? 50°C which indicated that the phase transition is one of first order type. A TMA thermogram showed that this transformation was associated with a rapid increase in the expansion coefficient. Such an increase in the lattice parameter might be attributed to the enhanced rotation of electric dipoles associated with the distorted NH4+ and SO42? ions. The distortion of both the ammonium and sulfate ions in addition to their expected orientational motion are suggested to be responsible for the ferroelectric behaviour of ammonium sulfate below ?50°C.A transition to a metastable hexagonal state at about ?40°C is thought to occur, and this transformation is found to be irreversible. 相似文献
19.
The polycrystalline samples of Sm2(MoO4)3 have been prepared by heating appropriate quantities of oxides. The X-ray powder diffraction technique has been used to provide
information about lattice parameter, space group and basic structure. The dielectric constant has been measured as a function
of frequency (560 Hz-13 MHz) and temperature (30–220°C) to know the ferroelectric transition temperature. 相似文献