铁电磁体Pb(Fe1/2Nb1/2)O3的磁电性能研究

对铁电磁体Pb(Fe_1/2Nb_1/2)O₃单晶样品中的 介电和磁性能进行了研究. 认为在其反铁磁相变点观察到的介电常数和损耗的异常来自于自发极化序和自旋序的相互作用 引起的磁电耦合. 磁矩与温度的关系曲线在Nel点以下的低温段呈上升趋势，测得的磁滞 回线证明有弱铁磁性出现. 对铁电磁体磁电相互作用的Monte Carlo模拟得到与实验类似的 结果. 关键词： 铁电磁体 1/2Nb_1/2)O₃')" href="#">Pb(Fe_1/2Nb_1/2)O₃ 磁电耦合 Monte Carlo模拟     

过渡族元素掺杂BaTiO3-Tb1-xDyxFe2-y层状复合材料中的磁电效应

用溶胶-凝胶法制备1.0%mol Mn,Cr,Co掺杂 BaTiO₃(BTO)粉体,在1350℃下烧结成多晶陶瓷样品.X射线衍射和差示扫描量热分析表明,室温下掺杂BaTiO₃具有四方钙钛矿结构;居里点和相变潜热随Cr,Mn,Co掺杂逐渐降低.将掺杂BaTiO₃与Tb_1-xDy_xFe_2-y(TDF)胶合制成双层磁电复合材料,并研究了Cr:BTO-TDF,Mn∶BTO-TDF,Co:BTO-TDF层状复合材料中的磁电效应.实验表明,在340×80 A·m^-1偏置磁场下, Cr:BTO-TDF的横向磁电电压系数达到最大值586 mV·cm^-1·(80 A·m^-1)^-1.在400×80 A·m^-1偏置磁场下,Mn∶BTO-TDF和Co:BTO-TDF的横向磁电电压系数的最大值分别为480 mV·cm^-1·(80 A·m^-1)^-1和445mV·cm^-1·(80 A·m^-1)^-1.研究表明掺杂BaTiO₃-TDF层状复合材料中具有较强的磁电耦合.作为无铅压电材料,掺杂BaTiO₃制备的磁电效应器件颇具应用前景. 关键词： 磁电效应 双层复合材料 3')" href="#">掺杂BaTiO₃ 1-xDy_xFe_2-y')" href="#">Tb_1-xDy_xFe_2-y     

Pr1/3Sr2/3FeO3中电荷有序现象的超声研究

系统研究了Pr1/3Sr2/3FeO3单相多晶样品在低温下的电荷输运性质和超声特性.电阻测量表明,Pr1/3Sr2/3FeO3在162K发生了电荷有序相变.而超声声速从室温开始就出现了明显的软化,在电荷有序温度附近达到最小值,随后又急剧硬化,同时伴随着一个巨大的衰减峰.分析指出这是由于电-声子相互作用导致的结果,该电-声子耦合可能起源于Fe4 的Jahn-Teller效应.     

单磁场驱动的Tb1-xDyxFe2-y/Pb(Zr,Ti)O3三层膜磁电效应

研究了Tb_1-xDy_xFe_2－y (TDF)与锆钛酸铅(PZT)三层膜样品的制备和在单一直流磁场驱动下的磁电(ME)效应. 在该系列三层膜样品中测量到了巨大的ME耦合效应. 所得实验结果与同种样品在两磁场驱动下的ME效应完全不同. 这可能预示了某些新的物理内容. 该技术可简化ME效应在某些实际应用中的复杂度. 关键词： 1-xDy_xFe_2－y')" href="#">Tb_1-xDy_xFe_2－y PZT 单磁场 ME效应     

Sm1－xGdxA12低温下的磁性

分别测量了Sm1-xGdxAl2在低温下不同外加磁场时的电阻和磁化率.实验 结果表明，铁磁性物质Sm1-xGdxAl2在居里温度以下时，自旋磁矩和轨 道磁矩反平行有序排列，且对温度的依赖关系不同，导致在磁性抵消点出现自旋铁磁有序而 总磁矩为零的磁现象.并发现外加强磁场时自旋 轨道发生翻转. 关键词： Sm1-xGdxAl2 铁磁有序 自旋磁矩 轨道磁矩     

La2/3Ca1/3MnO3超薄膜应力弛豫过程及性质研究

锰氧化物庞磁电阻材料超薄膜的应力弛豫特性的研究对理解这一强关联体系的特性及应用都具有重要的意义.为此,我们研究了不同温度退火的La2/3Ca1/3MnO3/LaAlO3超薄膜的形貌、结构、电输运特性等.发现退火导致的应力弛豫对薄膜的性质有很强的调制作用,其电输运性质及结构呈现明显的阶段性变化过程,我们提出了一个高温应力弛豫模型对所观察到的实验现象进行了解释.实验中观察到的规则的自相似网状纳米结构,显示了薄膜应力弛豫过程中自组织生长的分形特征.     

Sr2Fe1－xCoxMoO6体系中Co的元素替代效应

在成功制备具有双钙钛矿结构Sr₂Fe_1-xCo_xMoO₆系列样品的基础上，对其结构、输运性质和磁性质进行了系统研究.结果发现，随着Co替代浓度x值的增加，样品的电阻率-温度关系由半金属行为转变为半导体行为，其室温电阻率从3.9×10^-5Ω·cm增大到6.0×10^-1Ω·cm；样品由亚铁磁体转变成反铁磁体，其磁相变温度T_N值也随之下降; Co对Fe的部分替代使其磁电阻效应受到抑制.基于对其电子结构的分析，其磁电阻效应的起源以及Co的元素替代效应也在文中进行了讨论. 关键词： 双钙钛矿结构 2FeMoO₆')" href="#">Sr₂FeMoO₆ 磁电阻     

La2/3 Ca1/3 MnO3中绝缘体-金属相变与CMR效应

我们研究了超大磁阻材料La2/3Ca1/3MnO3的磁电特性,发现由电阻测量得到的绝缘体－金属相变与由磁化曲线得到的顺磁－铁磁相变温区完全一致,均随磁场的增强推向高温区。结果证明绝缘体－金属相变起因于磁序的变化,并伴随着越大磁电阻效应的CMR的发生。     

La1－xPrxMnO3(x=0.1，0.2)薄膜庞磁电阻性质的研究

一种新的庞磁电阻氧化物薄膜La_1-xPr_xMnO₃(x=0.1，0 .2)薄膜用脉冲激光沉积(PLD)方法生长在(100)SrTiO₃单晶基底上.XRD结果显示 薄膜具有很好的外延单晶取向.电输运和磁性质的研究表明薄膜具有显著的庞磁电阻效应(CM R)效应，其中磁电阻比率达95％(在5T的磁场下).X射线光电子能谱(XPS)的结果表明薄膜体 系中Pr离子的价态为+4价，因此该薄膜很可能是电子掺杂的庞磁电阻体系. 关键词： 脉冲激光沉积 1-xPr_xMnO₃')" href="#">La_1-xPr_xMnO₃ 电子 掺杂 庞磁电阻     

GaN/AlxGa1-xN异质结二维电子气的磁电阻研究

通过对GaN/Al_xGa_1-xN异质结中二维电子气磁输运结果的分析,研究了磁电阻的起因.结果表明,整个磁场范围的负磁电阻是由电子-电子相互作用引起的,而高场下的正磁电阻来源于平行电导的进一步修正.用拟合的方法得到了电子-电子相互作用项以及平行电导层的载流子浓度和迁移率,并用不同的计算方法对拟合结果进行了验证.     

A Quantum Monte Carlo Study on Mixed-Spin Chains of 1/2-1/2-1-1 and 3/2-3/2 -1-1

The ground-state and thermodynamic properties of quantum mixed-spin chains of1/2-1/2-1-1and 3/2-3/2-1-1are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it has two phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain, the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameterα=J2/J1.     

A Quantum Monte Carlo Study on Mixed-Spin Chains of 1／2-1／2-1-1 and 3／2-3／2-1-1

The ground-state and thermodynamic properties of quantum mixed-spin chains of 1/2-1/2-1-1 and 3/2-3/2-1-1 are investigated by a quantum Monte Carlo simulation with the loop-cluster algorithm. For 1/2-1/2-1-1 chain, we find it hastwo phases separated by an energy-gap vanishing point in the ground-state. For 3/2-3/2-1-1 chain,the numerical results show two energy-gap vanishing points isolated by different phases in its ground-state. Our calculations indicate that all these ground state phases can be understood by means of valence-bond-solid picture, and the thermodynamic behavior at finite temperatures is continuous as a function of parameter α=J2/J1.     

On the 2S1/2–1S1/2 photon-plasmon transition in hydrogenous atoms

The probabilities of the two-quantum induced (according to the number of plasmons) photon-plasmon transitions 2S_1/2–1S_1/2 are calculated for hydrogenous atoms. In a turbulent plasma medium this process may be more effective than conventional two-photon radiation and collisions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 2, pp. 305–307, February, 1972.The authors thank L. A. Vainshtein and Yu. P. Nikitin for discussing the work and for their valuable comments.     

(1/2+1/2+1)腔型热阴极微波电子枪

 介绍了一种新型的轴耦合热阴极微波电子枪的设计，该枪采用了缩短首腔以及在首腔与主加速腔间插入耦合半腔的设计思想，在不破坏粒子束性能的基础上尽量减小反轰功率，给出了用Superfish 及Pamela软件进行物理设计以及粒子动力学计算的结果，在脉冲宽度为6μs, 重复频率为25Hz时，阴极上平均反轰功率为3.6W,达到设计要求。     

1+3/2与1+1/2对转涡轮对比分析

为理清1 1/2对转涡轮及1 3/2对转涡轮使用范围和效能,从而帮助设计决策,本文采用Stewart方法,从速度三角形基本分析入手,以速功比为主要变量,考察、对比1 3/2和1 1/2对转涡轮性能特点.研究表明:各转速比下,1 3/2对转涡轮高效率范围都比1 1/2对转涡轮窄,但其高效区发生在更小的总速功比区域;随转速比绝对值增加,两种涡轮高效率区都增加,高效率区位置都偏向大的总速功比区域;相比于1 1/2对转涡轮,1 3/2对转涡轮具有较低出功比,且偏向于低速功比区域;随转速比绝对值增加,两种对转涡轮出功比范围均拓展.这些结果为未来先进航空发动机涡轮选型提供了重要借鉴.     

Luminescence properties of K1/2Bi1/2TiO3:Pr3+ and Na1/2Bi1/2TiO3:Pr3+

The luminescence properties of K(1/2)Bi(1/2)TiO(3):Pr(3+) and Na(1/2)Bi(1/2)TiO(3):Pr(3+) powders are investigated in the temperature range 10-600 K. The experimental data are interpreted on the basis of metal-to-metal charge transfer processes and by considering Bi(3+)-to-Pr(3+) sensitization effects.     

Magnetoelectricity in the PbFe1/2Nb1/2O3 Ceramics

The magnetodielectric effect (the influence of a magnetic field H on the dielectric constant ?) and the magnetoelectric effect (the influence of an electric field E on the magnetoelectric constant ??) of the PbFe_1/2Nb_1/2O₃ ceramics have been investigated at temperatures T in the range from 50 to 200°C, including the Curie point T _C ? 98°C. It has been demonstrated that there is a correlation of these effects with the shift of the ferroelectric-paraelectric phase transition temperature in a magnetic field.     

Crystal structures and phonon modes of Ba(Ca1/2W1/2)O3, Ba(Ca1/2Mo1/2)O3 and Ba(Sr1/2W1/2)O3 complex perovskites investigated by Raman scattering

This work investigates the crystal structures and phonon modes of Ba(Ca_1/2W_1/2)O₃, Ba(Ca_1/2Mo_1/2)O₃ and Ba(Sr_1/2W_1/2)O₃ perovskites by Raman spectroscopy. The samples were produced by conventional solid‐state processing at 1200 °C. X‐ray diffraction showed that single‐phase homogeneous materials were produced, which are cubic or pseudo‐cubic in symmetry. The existing controversies in the literature for these complex perovskites were investigated by comparing experimental Raman data with group‐theory analysis. Ceramics with Ca and W or Mo were found to be cubic, space group Fm3 m. For these materials, four Raman‐active bands were observed and the fitting parameters showed that the Ba(Ca_1/2Mo_1/2)O₃ ceramic presents bands at lower wavenumbers if compared with the Ba(Ca_1/2W_1/2)O₃ sample. For the Ba(Sr_1/2W_1/2)O₃ material, two hypotheses were investigated for monoclinic or triclinic structures. The experimental results showed 12 Raman‐active modes for this ceramic, which is in perfect agreement with the theoretical predictions for a monoclinic (I2/m) structure. Copyright © 2009 John Wiley & Sons, Ltd.     

Electromechanical and ferroelectric properties of (Bi1/2Na1/2)TiO3-(Bi1/2K1/2)TiO3- (Bi1/2Li1/2)TiO3-BaTiO3 lead-free piezoelectric ceramics for accelerometer application

Lead-free (0.90-x)(Bi_1/2Na_1/2)TiO₃-0.05(Bi_1/2K_1/2)TiO₃-x(Bi_1/2Li_1/2)TiO₃-0.05BaTiO₃ piezoelectric ceramics (abbreviated as BNKLBT-100x, with x ranged from 0 to 2.5 mol %) were prepared by a conventional mixed oxide method. Effects of the amount of (Bi_1/2Li_1/2)TiO₃ (BLT) on the electrical properties and crystal structure of the BNKLBT ceramics were examined. BNKLBT-1.5 ceramics have good properties with piezoelectric constant d₃₃=163 pC/N, electromechanical coupling factor k_p=0.33, k_t=0.53, relative permittivity ε_r=785 and dissipation factor cosδ=2.2% at 1 kHz. The sample has larger remnant polarization than BNKLBT-0 ceramics and the same coercive field as BNKLBT-0 ceramics. X-ray diffraction analysis shows that the incorporated BLT diffuses into the BNT–BKT–BT lattice to form a solid solution during sintering, but changes the crystal structure from rhombohedral to tetragonal symmetry at higher BLT amounts. Depolarization temperature (T_d) of the BNKLBT-100x ceramics increases from 102 °C to ∼136 °C for BNKLBT-0 to BNKLBT-2.5. BNKLBT-1.5 is used as the transduction element in compressive type accelerometer and its sensitivity is calibrated by the back-to back method. Within the ±2.5% tolerance, the lead-free accelerometer has a mean value of 2.97 pC/ms^-2 within 50 Hz–12.45 kHz and the lead-based accelerometer has a mean value of 4.34 pC/ms^-2 within 50 Hz to 8.24 kHz. PACS 77.22.Ej; 77.84.-s; 85.50.-n