铁电单晶Pb (Mg1/3Nb2/3)O3-PbTiO3的高场致应变及其在层叠式驱动器中的应用

通过研究(1_x)Pb(Mg_1/3Nb_2/3)O_{3_x}PbTiO3(PMNT)单晶在不同方向、不同组分下高场致应变的特性，确定了〈001〉取向 PMNT单晶（29％≤x≤31%）为制作层叠式驱动器的最佳组分范围，这组分的单晶具有高场致应变、低滞后而且性能较稳定的特点.研究结果表明，在保证应变曲线的线性和低滞后的前提下，将近-2kV/cm的负电场能够运用于〈001〉方向的PMNT晶体上. 40层（每片晶片尺寸为7mm×7mm×0.7mm）PM 关键词： PMNT单晶 场致应变 PMNT驱动器     

化学溶液法制备的Pb(Mg1/3 Nb2/3)O3-PbTiO3薄膜的光学性能

用化学溶液方法在宝石衬底及有LaNiO3缓冲层的Pt/TiO2/SiO2/Si衬底上制备了92%Pb(Mg1/3 Nb2/3)O3-8%PbTiO3(PMNT)薄膜,X射线衍射测试结果表明:在有LaNiO3缓冲层的Pt/TiO2/SiO2/Si衬底上制备的PMNT薄膜几乎是纯钙钛矿相,且薄膜呈现(110)择优取向.通过对Pt/TiO2/SiO2/Si衬底上的PMNT薄膜在2.5-12.6μm波长范围内的红外椭圆偏振光谱测试,并拟合得到了PMNT薄膜在2.5-12.6μm波长范围内的光学常数(n和k),通过对宝石衬底上的PMNT薄膜在200-1100nm波长范围内的可见-紫外透过率测试,并拟合得到了PMNT薄膜在200-1100nm波段的光学常数(n和k)和吸收系数α,进而推导出PMNT薄膜的禁带宽度为4.03eV.     

钛酸钡单晶沿垂直解理面方向的超高压电响应的研究

研究了钛酸钡单晶沿着解理面的压电响应. 首先发现在钛酸钡单晶中存在着解理面，当垂直 这一解理面方向施加电场时，得到了超过2000pC/N的超高压电常量d33. 而这一d 33值比沿着自发极化方向〈001〉方向施加电场得到的压电常量（d33〈001 〉=87pC/N）高20多倍. 而且，沿此方向在很低电场强度（低于1kV/mm）下得到了高达0 6%的应变值，这一应变值是同等场强下PMN_PT单晶的10倍之多. 这一结果无疑对发展无铅压 电材料驱动器提供了一种新可能. 关键词： 压电响应 解理面 钛酸钡单晶     

铁电单晶0.62Pb(Mg1/3Nb2/3)O3-0.38PbTiO3折射率的研究

用最小偏向角法在20℃下精确测量了0.62Pb(Mg_1/3Nb_2/3)O_{3< /sub>-0.38PbTiO3( 0.62PMN-0.38PT)单晶的折射率，给出了该温度下折射率色散的Sellmeier方程.研究了能带 结构与折射率的关系，计算了样品的Sellmeier光学系数：对no，E0=5.50eV,λ0=0.2 26μm，Ｓ０=1.004×10¹⁴m^-2，Ed=28.1 0eV；对ne，Ｅ0=5.57eV,λ 0=0.223μm，S0=1.017×10¹⁴m^-2，Ed=28.10eV.A BO3型钙钛矿材料中，BO6八面体基元决定了晶体的能带结构，对折 射率产生重要影响. 关键词： PMNT单晶 折射率 Sellmeier光学系数}     

新型压电单晶PMNT的生长、性能及应用

通过对PMN -PT二元体系在高温下的相结构、相稳定性以及相图的研究 ,确立了PMNT单晶的生长方法 ,用Bridgman方法生长出了大尺寸高质量的PMNT单晶 .目前制备的PMNT单晶尺寸达到40× 70mm ,晶片尺寸为2 0× 2 0× 1mm ,其主要性能为 :介电常数ε～ 5 0 0 0 ,介电损耗tanδ <0 9%,压电系数d3 3 >15 0 0pC N ,机电耦合系数k3 3～ 94%.在准同型相界附近 ,PMNT单晶的压电活性比较高 ,但其结构比较复杂 ,实际应用时应该考虑单晶的综合性能 ,生长组成略为离开相界的PMNT单晶 .在扫描电声显微镜中 ,我们将PMNT单晶用于其压电换能器 ,明显提高了电声像的分辨率 ,充分显示出PMNT在超声成像、水声换能器以及高应变驱动器中有广泛的应用前景 .     

掺铑BaTiO3单晶场致应变特性的研究

系统地研究了掺铑的BaTiO₃单晶在老化后的场致应变性能.研究发现，晶体的场 致应变随老化时间的增加而增大，在老化27天后，在300V/mm的电场下，其双向场致应变可达1.11％；在较小的测试频率下（0.01Hz）也可得到0.95％的可逆的巨大的单向场致应变，在低频范围内，晶体的单向场致应变随测试频率增大而减小；研究晶体老化后的电滞回线，发现其 形状类似于蜂腰磁滞回线.实验结果表明，对BaTiO₃单晶掺杂铑元素可以大大改 善其电致伸缩性能，可能产生新的在超大应变及非线性驱动器中的应用. 关键词： 3单晶')" href="#">BaTiO₃单晶 掺铑 场致应变 老化     

化学溶液法制备的Pb(Mg1/3Nb2/3)O3-PbTiO3薄膜的光学性能

用化学溶液方法在宝石衬底及有LaNiO₃缓冲层的Pt/TiO₂/SiO₂/Si衬底上制备了92%Pb(Mg_1/3Nb_2/3)O₃-8%PbTiO₃(PMNT)薄膜，X射线衍射测试结果表明：在有LaNiO₃缓冲层的Pt/TiO₂/SiO₂/Si衬底上制备的PMNT薄膜几乎是纯钙钛矿相，且薄膜 关键词： PMNT薄膜 光学性能 化学溶液法     

弛豫型铁电单晶0.67Pb(Mg_(1/3)Nb_(2/3))O_3-0.33PbTiO_3的拉曼散射研究

本文采用拉曼散射技术在温度从374到-196℃的范围内,研究了弛豫型铁电单晶0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3(PMNT)。观察了在不同温度下拉曼光谱的变化,经分析这些变化反映了该晶体经历了两个相变:第一个相变温度发生在120℃,从顺电立方相到铁电四方相的相变,780 cm-1处模式在VH偏振下的改变标志了这一相变;第二个相变温度发生在34℃,是从铁电四方相到铁电三方相的相变,软模的出现代表了这一相变。     

铁电单晶0.62Pb(Mg1/3Nb2/3)O3-0.38PbTiO3折射率的研究

用最小偏向角法在20℃下精确测量了0.62Pb(Mg1/3Nb2/3)O3-0.38PbTiO3(0.62PMN-0.38PT)单晶的折射率,给出了该温度下折射率色散的Sellmeier方程.研究了能带结构与折射率的关系,计算了样品的Sellmeier光学系数:对no,E0=5.50eV,λ0=0.226μm,S0=1.004×1014m-2,Ed=28.10eV;对ne,E0=5.57eV,λ0=0.223μm,S0=1.017×1014m-2,Ed=28.10eV.ABO3型钙钛矿材料中,BO6八面体基元决定了晶体的能带结构,对折射率产生重要影响.     

掺铑BaTiO3单晶场致应变特性的研究

系统地研究了掺铑的BaTiO3单晶在老化后的场致应变性能.研究发现,晶体的场致应变随老化时间的增加而增大,在老化27天后,在300V/mm的电场下,其双向场致应变可达1.11%;在较小的测试频率下(0.01Hz)也可得到0.95%的可逆的巨大的单向场致应变,在低频范围内,晶体的单向场致应变随测试频率增大而减小;研究晶体老化后的电滞回线,发现其形状类似于蜂腰磁滞回线.实验结果表明,对BaTiO3单晶掺杂铑元素可以大大改善其电致伸缩性能,可能产生新的在超大应变及非线性驱动器中的应用.     

Physical properties of BaMg1/3Nb2/3O3-BaCo1/3Nb2/3O3 solid solutions

Structural, electric and magnetic properties of Ba₃Mg_1−xCo_xNb₂O₉ based dielectric ceramic compounds have been studied. The samples, prepared by a solid state reaction method, were characterised by X-ray powder diffraction (XRPD), electron microscopy (SEM), dielectric (ε(T)) and magnetic measurements (χ⁻¹(T)). The XRPD analyses showed that the crystal structure of these compounds does change by the increase of substitution degree, passing from a superstructure hexagonal-type, (no. 164), space group (SG) to a simple structure cubic-type, (no. 221), SG. However, the evolution of the elementary unit cell lattice parameter can be followed and it exhibit a linear increasing tendency with increase in the substitution, indicating the existence of a solid solution through out the investigated range of substitution (0-1). The microstructure analysis shows a variation in the grain size and also the porosity of the samples with the degree of substitution. The results are in good agreement with that of dielectric measurements, which also showed that the dielectric constant (ε) increases with the increase of cobalt content. The magnetic characterization of cobalt substituted samples showed an antiferromagnetic type super-exchange interaction between these magnetic ions. At the same time, the values of effective magnetic momentum (μ_eff) are close to the value that corresponds to Co²⁺ free ions. The study highlights the possibility of modelling these materials by substitutions, in order to improve properties of negative-positive-zero (NPO) type dielectric applications.     

La0.67Ca0.33MnO3薄膜皮秒光电效应

在1064 nm波长脉冲激光（脉宽25 ps）的照射下，钙钛矿氧化物薄膜La0.67Ca0.33MnO3/SrTiO3具有超快光电效应，对激光脉冲显示ps量级的响应时间，上升沿响应时间300 ps，半高宽700 ps，同时，对激光能量的响应灵敏度为500 mV/mJ。     

Temperature-dependent photoluminescence in La2/3Ca1/3MnO3

Visible photoluminescence and its temperature dependence of La_2/3Ca_1/3MnO₃ in the temperature range 138-293 K were measured. It was observed that the main broad band centered at ∼1.77 eV with the shoulders at ∼1.57 and ∼1.90 eV existed in the entire temperature range. It can be well fitted by three Gaussian curves B₁, B₂ and B₃ centered at ∼1.52, ∼1.75 and ∼1.92 eV, respectively. The intensities of the peak B₁ and B₂ vary as temperature increases. In the entire temperature range, the intensity of B₁ increases with increasing temperature, whereas that of B₂ decreases. The photoluminescence mechanisms for La_2/3Ca_1/3MnO₃ are presented based on the electronic structures formed by the interactions among spin, charge and lattice, in which B₁ was identified with the charge transfer excitation of an electron from the lower Jahn-Teller split e_g level of a Mn³⁺ ion to the e_g level of an adjacent Mn⁴⁺ ion, B₂ is assigned to the transition between the spin up and spin down e_g bands separated by Hund's coupling energy E_J and B₃ is attributed to the transition, determined by the crystal field energy E_C, between a t_2g core electron of Mn³⁺ to the spin up e_g bands of Mn⁴⁺ by a dipole allowed charge transfer process.     

Giant dielectric relaxation in SrTiO3-SrMg1/3Nb2/3O3 and SrTiO3-SrSc1/2Ta1/2O3 solid solutions

Ceramic samples of (1−x)SrTiO₃-xSrMg_1/3Nb_2/3O₃ and (1−x)SrTiO₃-xSrSc_1/2Ta_1/2O₃ were prepared, and their dielectric properties were studied at x=0.005–0.15 and 0.01–0.1, respectively, at frequencies 10 Hz–1 MHz and at temperatures 4.2–350 K. A giant dielectric relaxation was observed in the temperature range 150–300 K, and not so strong but well-developed relaxation was found in the temperature range 20–90 K. The activation energy U and the relaxation time τ₀ were determined to be 0.21–0.3 eV and from 10⁻¹¹ to 10⁻¹² s for the high-temperature relaxation and 0.01–0.02 eV and 10⁻⁸–10⁻¹⁰ s for the low-temperature relaxation, respectively. The additional local charge compensation of the heterovalent impurities Mg²⁺ and Nb⁵⁺ (or Sc³⁺ and Ta⁵⁺) by free charge carriers or the host ion vacancies is suggested to be the underlying physical mechanism of the relaxation phenomena. On the basis of this mechanism, the Maxwell-Wagner model and the model of reorienting dipole centers Mg²⁺ (or Sc³⁺) associated with the oxygen vacancy are proposed to explain the high-temperature relaxation with some arguments in favor of the latter model. The polaron-like model with the Nb⁵⁺-Ti³⁺ center is suggested as the origin of the low-temperature relaxation. The reasons for the absence of ferroelectric phase transitions in the solid solutions under study are also discussed. From Fizika Tverdogo Tela, Vol. 44, No. 11, 2002, pp. 1948–1957. Original English Text Copyright ? 2002 by Lemanov, Sotnikov, Smirnova, Weihnacht. This article was submitted by the authors in English.     

Polarization characteristics of the relaxor ceramics of multicomponent system with PbNb2/3Zn1/3O3, PbNb2/3Mg1/3O3, and PbTiO3

The phenomenon of dielectric hysteresis in the relaxor ceramics of multicomponent system with PbNb_2/3Zn1/₃O₃, PbNb_2/3Mg_1/3O₃, PbTiO₃ has been studied. The influence of different modifiers on polarization characteristics is examined and the correlations of these properties with the phase and chemical composition of the ceramics are investigated. The results obtained can be used to predict relaxor properties.     

La2/3Ca1/3MnO3/Eu2CuO4/La2/3Ca1/3MnO3磁性隧道结的制备与表征

采用磁控溅射，紫外线光刻和离子束刻蚀制备了La_2/3Ca_1/3MnO₃/Eu₂CuO₄/La_2/3Ca_1/3MnO₃磁性隧道结.通过对获得的磁性隧道结的I-V特性测量，发现非线性的I-V特性，显示结样品的隧穿特性.有趣的是发现在电极材料La_2/3Ca_1/3MnO₃的金属-绝缘体转变温度(Tp)以下，I-V曲线出现一个跳变.随着温度降低，开始出现跳变的临界电流增大，但是跳变都发生在同样的电压下～209mV.当电流增大或减小在跳变点附近出现回滞.这一跳变只发生在铁磁金属态，表明这是一个磁性相关联的效应，可能对应一种新的磁性开关过程.虽然，目前对这一现象背后的物理机理还不清楚，但是，这一现象有可能在未来自旋电子学器件方面具有潜在的应用价值. 关键词： 庞磁电阻 磁性隧道结 开关效应     

E-T phase diagrams of a solid solution of the multicomponent PbZn1/3Nb2/3O3-PbMg1/3Nb2/3O3-PbNi1/3Nb2/3O3-PbTiO3 system near the morphotropic phase boundary

The specific features of the dielectric and pyroelectric responses of a solid solution in the barium-doped multicomponent yPbZn_1/3Nb_2/3O₃-mPbMg_1/3Nb_2/3O₃-nPbNi_1/3Nb_2/3O₃-xPbTiO₃ system of the composition y = 0.0982, m = 0.4541, n = 0.1477, and x = 0.3 near the morphotropic phase boundary have been investigated. It has been assumed that the maxima revealed in the dependences of the reversible permittivity on the electric field strength with both the forward and backward changes in the field (E ₌) are associated with the induced phase transition. Based on the experimental results, the E-T phase diagrams are constructed in the temperature range from ?100 to 150°C for different temperature-field regimes: (i) variation in the electric field E ₌ at a fixed temperature of the sample and (ii) variation in the temperature of the sample at a constant value of E ₌. It has been found that there is a singular point in the E-T phase diagram and that, in the vicinity of this point, the dielectric and pyroelectric responses of the studied ceramics exhibit specific features.     

Spin-polarized tunneling in nanostructured La2/3Sr1/3MnO3

We present magnetic and transport properties of nanocrystalline La_2/3Sr_1/3MnO₃ powders prepared by a gel-combustion method using citric acid as the fuel. The coercive magnetic field H_c is significantly different to the field H_c^* for which the magnetoresistance (MR) is maximum. The MR at low fields (LFMR) exhibits a power-law dependence with magnetization, MR∝Mⁿ, with n=2.5–3.3 for temperatures ranging from 5 to 200 K. The results are discussed in terms of a distribution of particle size in our sample.     

Electric and magnetic behaviour in double doped La2/3＋4x/3Sr1/3-4x/3Mn1-xMgxO3

The double-doped La2/3＋4x/3Sr1/3-4x/3Mn1-xMgxO3 samples with fixed Mn^3＋/Mn^4＋ ratio equal to 2/1 are investigated by means of magnetism and transport measurements. Phase separation is observed at temperature higher than T^onset c for x = 0.10 and 0.15. For x = 0.10, rather strong phase separation induces drastic magnetic random potential and results in the localization of carriers. Thus, the varlable-range hopping process dominates. For other samples, there is no or only weak phase separation above T^onset c. Thus, thermal activation mechanism is responsible for the high temperature transport behaviour. For x = 0.20 and 0.25, unexpected AFM behaviour is observed at low temperature. All these results are well understood by considering the special role of the ＂double-doping＂.     

对靶溅射技术制备的La2/3Ca1/3MnO3/YBa2Cu4O8/La2/3Ca1/3MnO3薄膜中Tc的降低

本文用对靶溅射技术制备了La2/3Ca1/3MnO3/YBa2Cu4O8/La2/3Ca1/3MnO3薄膜.与YBCO单层薄膜相比,由于超导/铁磁系统中的磁性邻近效应,三层薄膜表现出较低的超导转变温度.薄膜的R～T测量曲线显示出超磁阻(CMR)效应和超导转变,预示着超导和铁磁特性共存于LCMO/YBCO/LCMO三文治结构.