半掺杂Sm0.5Ca0.5MnO3体系的电荷有序和再入型自旋玻璃行为

研究了半掺杂锰氧化物Sm0.5Ca0.5MnO3体系的结构、输运和磁特性,结果表明,在半掺杂情况下,该体系呈现O′类正交结构,表明体系存在典型的Jahn-Teller效应畸变;输运结果在整个测量温区均呈现半导体导电行为,没有出现金属-绝缘体(M-I)转变和CMR效应;电荷有序转变发生在T=270K左右,反铁磁转变温度出现在200K附近,且表现出典型的再入型自旋玻璃(spin-glass)行为,自旋玻璃转变温度TSG在41K附近,同时,观察到了存在于该体系中负的磁化异常,表明半掺杂的Sm0.5Ca0.5MnO3基态存在有多种复杂而丰富的磁相互作用之间竞争机制,其研究将为强关联锰氧化物体系物理机理的理解提供丰富的实验资料.     

相分离Nd0.5Ca0.5MnO3体系的再入型自旋玻璃行为和电荷有序

研究了Nd_0.5Ca_0.5MnO₃体系的结构和输运特性. 结构 分析表明，在300K下，体系表现为O′型正交结构并存在典型的Jahn-Teller畸变.在8 T磁场 下，体系出现顺磁绝缘-铁磁金属的转变，庞磁电阻效应发生. 磁测量发现，样品的奈尔温 度T_N和电荷有序转变温度T_CO分别在150和240K左右，在41K左右出 现典型再入型自旋玻璃行为，同时观察到了负的磁化率异常. 结果表明，Nd关键词： 庞磁电阻 自旋玻璃态 负磁化强度 电荷有序     

0.5PZN-0.5PZT压电陶瓷拉曼散射研究

PZT基多元系压电陶瓷在三方相含量与四方相含量相等的准同型相界处(MPB)具有极为优异的压电性能。文章采用拉曼散射方法研究了0.5PZN-0.5PZT陶瓷体系中三方-四方相共存与弥散相变现象。研究发现,与纯PZT相比,0.5PZN-0.5PZT体系拉曼谱呈明显宽化特征,表明体系弛豫性较强,依据介温谱计算出弥散因子γ高达1.71。通过对拉曼谱峰进行Gauss函数拟合,定量计算三方相R₁模式与四方相E(3TO)和A₁(3TO)模式相对强度,以及四方相E(4LO)和A₁(3LO)模式与三方相R_h模式相对强度,结果表明0.5PZN-0.5PZT体系三方相与四方相含量相等,组成位于准同型相界,该结果得到XRD相分析验证。电学测量表明0.5PZN-0.5PZT陶瓷压电性能优异：k_p=0.66, d₃₃=425 pC/N,适宜作为压电致动器材料使用。     

半掺杂Sm0.5Ca0.5MnO3体系的电荷有序和再入型自旋玻璃行为

研究了半掺杂锰氧化物Sm_0.5Ca_0.5MnO₃体系的结构、输运和磁特性，结果表明，在半掺杂情况下，该体系呈现O′类正交结构，表明体系存在典型的Jahn-Teller效应畸变；输运结果在整个测量温区均呈现半导体导电行为，没有出现金属－绝缘体(M-I)转变和CMR效应；电荷有序转变发生在T=270K左右，反铁磁转变温度出现在200K附近，且表现出典型的再入型自旋玻璃(spin-glass)行为，自旋玻璃转变温度T_SG在4 关键词： 自旋玻璃 电荷有序 负磁化现象 多相竞争     

相分离Eu0.5Sr0.5MnO3体系中的场诱导磁相变及输运特性研究

研究了半掺杂相分离锰氧化物Eu0.5Sr0.5MnO3样品的结构和电磁输运特性.在半掺杂情况下,该样品呈O′型正交结构,表明样品存在典型的Jahn-Teller畸变;在75 K附近样品的顺磁/反铁磁背景中开始出现铁磁相,在更低的温度42 K,4000 A/m磁场下M-T的场冷曲线和零场冷曲线出现明显分岔,样品的交流磁化率实部随温度的变化曲线中也在42 K观察到尖峰的出现,表现出团簇玻璃行为.在无外加磁场下该样品在整个测量温区均呈现绝缘体型导电行为,而在外加磁场1.6×106 A/m下出现磁场诱导的绝缘体-金属 (I-M)转变,其电输运特性符合可变程跳跃模型;研究表明,半掺杂Eu0.5Sr0.5MnO3样品的基态存在多种复杂而丰富的磁相互作用之间的竞争机理,其研究将为强关联锰氧化物体系物理机理的理解提供丰富的实验资料.     

共掺杂稀土配合物Tb0.5Eu0.5(TTA)3Dipy发光性质的研究

以TTA为TTA配体合成了新的共掺杂稀土配合物Tb0.5 s Eu0.5(TTA)3 Dipy,通过与PVK的掺杂,分析了PVK 和Tb0.5Eu0.5(TTA)3Dipy之间的能量传递过程,并且制备了以PVK:Tb0.5Eu0.5(TTA)3Dipy为发光层的结构为ITO/PVK:Tb0.5 Eu0.5(TTA)3 Dipy/PBD/Al的发光器件,通过改变两者之间的质量比,得到了较纯的Eu3 的红色发光.通过与PVK:Eu(TTA)3混合体系的比较,发现Tb3 的引入,起到了能量传递桥梁的作用,提高了PVK 到Eu3 的能量传递,从而抑制了PVK 的发光.因此,通过引人适当的第二种金属离子,会增强另一稀土离子的发光,是作者提高稀土离子发光效率的一种有效的手段.     

Nd0.5Ca0.5Mn0.97Co0.03O3体系的超声研究

系统研究了Nd0.5Ca0.5Mn0.97Co0.03O3单相多晶样品在低温下的电磁性质和超声特性.超声测量结果表明,体系在低温下超声声速出现异常,超声声速从室温开始随着温度的降低逐渐减小,并在220K附近声速达到最小,其相对变化(ΔV/V)超过2%.之后,随着温度的进一步降低,声速急剧硬化,其相对变化达到14.5%.分析表明这是由于体系中电-声子相互作用导致的电荷有序态转变的结果,该电声子耦合来源于Mn3 的JahnTeller效应.同时,该体系在100K左右出现了金属绝缘体转变同时伴随着铁磁相变,分析表明在低温下Co离子与Mn离子之间存在着铁磁交换作用,因此微量的Co掺杂会在反铁磁区域内形成部分铁磁小团簇,当铁磁团簇连通后,体系由反铁磁电荷有序态(AFMCO)向铁磁金属态(FMM)转变.研究结果表明了样品在电荷有序相变温度TCO与金属绝缘体转变温度TMI之间(TMI相似文献   

LiNi_(0.5)Mn_(0.5)O_2制备及表征

采用共沉淀法制备了LiNi0.5Mn0.5O2.XRD,Raman测试都表明材料是六方结构.XPS检测得出镍主要以正二价存在,锰元素主要以正四价存在.合成的LiNi0.5Mn0.5O2得到了50次的循环,但比容量较低.充放电循环性能比较研究表明,经过40次循环后,0.3,0.6,1.5 C的放电比容量分别是65.88,61.56,52.23 mA.h.g-1.     

钙钛矿锰氧化物(Nd1-xLax)0.5Ca0.5MnO3体系中的铁磁再入现象

研究了(Nd1-xLax)0.5Ca0.5MnO3(0≤x≤0.5)体系的X射线衍射谱,Raman吸收谱和电输运特性.通过电输运性质的测量给出了金属绝缘转变温度Tm与A位离子平均半径之间的关联.结果表明,La3 离子的掺杂压制低温下的电荷有序,导致金属绝缘转变开始出现,且随掺杂浓度的增加,金属绝缘转变(MI)温度(Tm)向高温区移动,对应的峰值电阻率ρp降低.X射线衍射谱和电输运特性均表明,La3 离子的掺入使得A位平均离子半径(〈rA〉)增大,导致局部晶格畸变减小.在掺杂量0.3≤x≤0.5的区域范围内,随着x的增加,双交换作用逐渐增强,有利于低温下铁磁态的形成.但热循环实验的研究结果表明,这种铁磁态属于亚稳态,在能量上反铁磁态比铁磁态更稳定.     

Fe0.5Cu0.5BaSrYCu2Oy化合物的结构和超导电性研究

实验采用常压和高压分别制备出含铁的FexCu1-xBaSrYCu2Oy（x= 0～1）系列化合物，本文主要研究x=0.5时样品的结构和超导电性.测量结果显示，高压合成的样品均具有超导电性，对于x=0.5的样品超导转变温度Tc(onset)～57K， Tc(0)～40K，而常压合成的样品当Fe含量x>0.3时均不超导.为此，我们利用透射电子显微镜（TEM）研究了该体系的微观结构特性，并通过电子能量损失谱(EELS)揭示出高压合成导致样品中载流子浓度明显高于常压样品，证明样品制备过程中高压有利于超导电性的形成.同时对高压样品中的缺陷和局域晶体结构畸变进行了深入分析.     

Characterisation of the reduction properties of La0.5Sr0.5Fe0.5Co0.5O3

We report here on the characterisation by temperature programmed reduction, ⁵⁷Fe Mössbauer spectroscopy and X-ray absorption spectroscopy of the phases resulting from treatment of the perovskite-related material La_0.5Sr_0.5Fe_0.5Co_0.5O₃ in a flowing 90% hydrogen/10% nitrogen atmosphere. The results show that treatment of La_0.5Sr_0.5Fe_0.5Co_0.5O₃ (which contains approximately 50% Fe⁴⁺ and 50% Fe³⁺) in the flowing 90% hydrogen/10% nitrogen atmosphere at 600°C does not result in the reduction of any of the constituent elements of the material and that the perovskite structure is still retained. The Mössbauer spectrum recorded following heating in the gaseous reducing environment at 1,000°C shows the presence of metallic iron, an Fe³⁺-containing phase with parameters compatible with the presence of SrLaFeO₄ which has a K₂NiF₄-type structure, and a paramagnetic Fe³⁺ phase. The X-ray absorption spectroscopy results show the presence of metallic cobalt. The Mössbauer spectrum recorded following heating at 1,200°C continues to show the Fe³⁺-containing components plus a larger contribution from metallic iron. The X-ray absorption spectroscopy results show the presence of metallic cobalt, SrLaFeO₄, La₂O₃ and SrO.     

Crystal structure and the magnetic state of Pr0.5Sr0.5Co0.5Fe0.5O3

The magnetic properties and crystal structure of the Pr_0.5Sr_0.5Co_0.5Fe_0.5O₃ compound are studied by neutron and x-ray diffractions using synchrotron radiation. These measurements show that this compound is a dielectric spin glass with a magnetic moment freezing temperature of about 70 K. As temperature decreases in the range 30–95 K, a structure phase transition of the first order occurs with an increase in the symmetry from orthorhombic (space group Imma) to tetragonal (space group I4/mcm). It is assumed that the transition is caused by a change in the 4f electron configuration of the Pr³⁺ ions.     

Ab initio study of Os0.5W0.5B2, Re0.5W0.5B2, and Os0.5Re0.5B2 with high shear modulus

By using first‐principles calculations, the authors investigate the structural, mechanical, and electronic properties of experimentally synthesized Os_0.5W_0.5B₂. The calculated structural parameters and elastic properties are in good agreement with the experimental results. In addition, two new 5d transition‐metal diborides (Re_0.5W_0.5B₂ and Os_0.5Re_0.5B₂) are predicted to have promising large shear moduli. The latter mainly come from the non‐uniform distribution of valence charge density, which raises the value of the shear moduli. We discuss potentially high hardness in these materials. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Energy sublevels in an Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As quantum wire

We report the successful fabrication of a V-grooveAl_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As quantum wire system and the temperature-dependent photoluminescence (PL) measurement. The PL spectra are dominated by four features at 681, 642, 635 and 621 nm attributed to the luminescences from quantum wire, top, vertical and side-wall well regions by micro-PL measurements. By the calculations of the energy structure, discrete states (localized sublevels) in the quantum wire region and continuum states (extended along the side-wall and vertical quantum wells) in side-wall and vertical quantum wells have been obtained in both the conduction and valence bands. The calculated excitation energies explain very well the peak positions and their temperature dependence in the photoluminescence measurements.     

High-temperature impedance spectroscopy of BaFe0.5Nb0.5O3 ceramics doped with Bi0.5Na0.5TiO3

Bi_0.5Na_0.5TiO₃ (BNT)-doped BaFe_0.5Nb_0.5O₃ (BFN) ceramics were synthesized by a two-step solid-state reaction. Temperature dependence of dielectric properties measured at different frequencies was investigated over broad temperature and frequency ranges. Impedance spectroscopy and universal dielectric response were employed to study the relaxation behavior and conductivity mechanism of the ceramics in a frequency range from 40 Hz to 100 MHz and a temperature range from 300 K to 800 K. The complex plane impedance data revealed the bulk and grain boundary contributions toward conductivity processes in the form of semicircular arcs. The high-temperature conductivity of ceramics is attributable to thermally activated second ionized oxygen vacancy.     

Intrinsic pinning properties of FeSe0.5Te0.5

The intrinsic pinning properties of FeSe_0.5Te_0.5, which is a superconductor with a critical temperature T_c of approximately 14 K, were studied through the analysis of magnetization curves obtained using an extended critical state model. For the magnetization measurements carried out with a superconducting quantum interference device (SQUID), external magnetic fields were applied parallel and perpendicular to the c-axis of the sample. The critical current density J_c under the perpendicular magnetic field of 1 T was estimated using the Kimishima model to be equal to approximately 1.6 × 10⁴, 8.8 × 10³, 4.1 × 10³, and 1.5 × 10³ A/cm² at 5, 7, 9, and 11 K, respectively. Furthermore, the temperature dependence of J_c was fitted to the exponential law of J_c(0) × exp(?αT/T_c) up to 9 K and the power law of J_c(0) × (1 ? T/T_c)ⁿ near T_c.     

0.5BiFeO3–0.5PbFe0.5Nb0.5O3 Multiferroic Ceramic: Structure,Dielectric and Magnetodielectric Properties

Physics of the Solid State - The structure, dielectric characteristics, and magnetoelectric effect of a 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 multiferroic ceramics are studied. We found that the...     

Phase transitions in PbSc0.5Ta0.5O3

Ordered and partially ordered PbSc_0.5Ta_0.5O₃ ferroelectric single crystals are studied by diffraction, electrophysical, and optical methods. X-ray diffraction and electrophysical methods indicate the presence of a phase transition in the low-temperature range (at T = ?40°C).     

Negative and persistent photoconductivity in p-type Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As heterostructures under uniaxial stress

Abstract

Illumination of a double p-Al_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As heterostructure by a red light emitting diode results in a negative photoconductivity that, after the diode is switched off, slowly relaxes to a positive persistent photoconductivity, characterised by an approximately 1.5-fold increase of the two-dimensional hole concentration. This metastable state may be explained with a model in which deep electron traps are supposed to be located above the Fermi level on the inverted heterointerface. Under uni-axial compression the hole concentration in the persistent photoconductivity state, as well as in the dark state, demonstrates the same linear decrease.