Structural phase transition in superconducting BaPb0.75Bi0.25O3

The room temperature crystallographic properties of distorted perovskite-type system BaPb_1-xBi_xO₃ were examined by using X-ray diffraction analysis. In addition, structural temperature changes were investigated for superconducting BaPb_0.75Bi_0.25O₃ crystals with T_c=11.4K. It was found that the room temperature structure of BaPb_1-xBi_xO₃ has an orthorhombic symmetry in the range of O≤×?0.9 and a monoclinic one in 0.9?×≤1, and that superconducting BaPb_0.75Bi_0.25O₃ shows a structural transition from an orthorhombic to a monoclinic phase at about 160K.     

Li2Mo2-xWxO6多晶材料的结构、电学性能与导电机理的研究

本文采用还原气氛制备导电性能优良的多晶多相陶瓷材料Li₂Mo_2-xW_xO₆(x=0,0.1,0.3),采用粉末X射线衍射分析、特征X射线能谱分析、红外光谱分析和电子自旋共振波谱分析等现代测试手段,得到样品的物相结构为Li₂Mo_1-xW_xO₄和MoO₂两相组成。W的掺入主要取代Mo进入Li₂ 关键词：     

Li1+xGe2-xAlxP3O12系统的相关系和电导

本文研究了Li_1+xGe_2-xAl_xP₃O₁₂系统的相组成和电导的关系。发现用LiGe₂P₃O₁₂作为基体化合物,通过离子置换可以得到好的锂离子导体。用Al³⁺置换LiGe₂P₃O₁₂中的Ge⁴⁺,在0关键词：     

Gd3Al2-xGax合金的磁熵研究

用磁控电弧炉在氩气气氛中熔炼了Gd₃Al_2-xGax(x=0,0.1,0.3,0.5)系列合金.通过X射线粉末衍射和振动样品磁强计研究了样品的结构和磁熵.发现样品都是由Zr₃Al₂相组成的,且GdAlGa系列合金的ΔS_m要比Gd₃Al₂的大,峰值在室温附近,温区较宽,是一种较好的磁致冷材料. 关键词：     

Na3Zr2-xInxSi2-xP1+xO12系统的组成、结构和离子电导的关系

用固相反应、X射线衍射、金相显微镜观察、测定比热和复平面阻抗谱的方法研究了Na₃Zr_2-xIn_xSi_2-xP_1+xO₁₂系统。在此系统中存在两种固溶体:单斜固溶体(0≤x<0.8)和三方固溶体(0.8≤x≤1.8)。即从x=0.8的组成开始,NASICON型Na₃Zr_2-xIn_xSi_2-x 关键词：     

Anomalous behavior of ultrasonic properties near 50 K in Rb0.30MoO3 and Rb0.30(Mo1−xVx)O3

Depending on the temperature, the charge density wave (CDW) nonlinear conductivity of the blue bronzes A_0.30MoO₃ (A=K, Rb) shows two different regimes: a strongly damped motion above ∼50 K and motion with almost no damping below ∼50 K. In a search for an elastic signature of this CDW behaviour, we performed ultrasonic measurements on Rb_0.30MoO₃ and Rb_0.30(Mo_1−xV_x)O₃ single crystals between 4 K and 300 K. In Rb_0.30MoO₃, at T∼50 K, upon cooling, a large increase of the sound velocity is observed. The ultrasonic attenuation coefficient shows an increase down to 50 K followed by a plateau. In Rb_0.30(Mo_1−xV_x)O₃ (x=0.4 at%) the anomaly broadens and is shifted towards higher temperatures. The results are discussed in terms of CDW glass.     

Synthesis, characterization and melt processing of Y1−x(Yb0.9Nd0.1)xBa2Cu3Oz superconductors

Effects of a combined substitute of Yb and Nd on Y site on the superconducting properties of YBa₂Cu₃O_y have been studied. We synthesized Y_1−x(Yb_0.9Nd_0.1)_xBa₂Cu₃O_z compound with x = 0.2, 0.4, 0.6, 0.8 and 1.0. Here, the ratio of Yb–Nd was fixed to be 9:1 for obtaining 123 phase without secondary phases. The melt processing thermal profiles for Y_1−x(Yb_0.9Nd_0.1)_xBa₂Cu₃O_z with x = 0.2 and 0.4 and the addition of 40 mol% {Y_1−x(Yb_0.9Nd_0.1)_x}₂BaCuO₅ and 0.5 wt% Pt in air were determined on the basis of the thermal analysis results. All samples showed a low grain growth rate, particularly for high x values, which may be partially ascribed to un-optimized thermal schedules. Although almost all the samples exhibited low J_c values, the sample with x = 0.2 exhibited T_c of 88.8 K and a relatively high J_c value of 16,000 A/cm² at 77 K for H//c-axis.     

Li2Mo2O6多晶材料的结构与电性能的研究

本文用固相反应烧结制备出Li₂Mo₂O₆多晶材料。经X射线分析、红外光谱和电子顺磁共振谱(EPR)的研究,确定了它的结构是Li₂Mo₂O₄和MoO₂两个晶相组成的烧结体。钼离子以四价状态存在于MoO₂晶相结构中。采用交流阻抗谱分析了晶界与温度变化的相关性。测得了样品的ln(σ_总T)-1/T 曲线是由两段直线和一段曲线所组成;总电导率化能σ_27℃=1.36×10^-3(Ω·cm)^-1,σ_115℃=1.49×10^-3(Ω·cm)^-1,σ_300℃=9.71×10^-3(Ω·cm)^-1,σ_370℃=2.42×10^-3(Ω·cm)^-1;电导活化能E₁=0.043eV,E₂=0.235eV,E_平均=0.76eV。采用维格纳极化电池法测得电子电导率σ_e,σ_e27℃=2.240×10^-5(Ω·cm)^-1,σ_e300℃=4.476×10^-3(Ω·cm)^-1。实验证明,室温下材料为固体电解质,300℃附近为良好的离子与电子混合导体。 关键词：     

R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性研究

在制备出Gd₃(Fe_1-xCo_x)_29-yCr_{y化合物基础上，成功制备出Sm3(Fe1-xCox)29 -yCry化合物，通过x射线衍射和热磁分析对R3(Fe1-x< /sub>Co x)29-yCry 关键词： 3(Fe1-xCox)29-yCry化合物')" href="#">R3(Fe1-xCox)29-yCry化合物 相结构 单轴磁晶各向异性}     

Structure dependence of near-infrared stimulated blue emission in polycrystalline Ln2(WO4)3 (Ln=Gd and Lu) doped with Tm and Yb

Tm- and Yb-doped gadolinium tungstate, (Gd_xTm_yYb_1−x−y)₂(WO₄)₃ (x=0.7-0.9; y=0.001-0.01), have been prepared by the polymerized complex method to achieve a homogeneous dispersion of dopants and to stabilize the host structure. Decomposition (900 °C 5 h) of the precursors with x=0.8-0.9 yielded a pure monoclinic phase, while that of x=0.7 resulted in formation of an orthorhombic impurity. The monoclinic phase exhibits bright up-converted blue emission due to the ¹G₄→³H₆ transition of Tm³⁺ (472 nm) upon excitation into the Yb³⁺:²F_7/2→²F_5/2 absorption band as a result of energy transfer from Yb to Tm. The orthorhombic impurity acts as a strong quencher of emission, and the quenching mechanism has been discussed on the basis of structural and spectroscopic properties of orthorhombic Lu₂(WO₄)₃:Tm,Yb prepared by the same method.     

Structure, dielectric and magnetodielectric properties of Bi1-xGdxFeO3 Ceramics

Different magnetodielectric effects were observed in Bi1-xGdxFeO3 ceramics depending on gadolinium content. A positive one was observed in the samples with x ≤0.10 at 295K and 16K, and a negative one in the sample with x = 0.4 at 16 K. Structure analysis by x-ray diffraction (XRD) reveals that the samples crystallize in the R3c structure (ferroelectrics) for x<0.08 and in the Pbnm structure (paraelectrics) for x≥0.3 at room temperature. Temperature-dependent dielectric response and x-ray diffraction confirm the occurrence of a structural transition in the Pbnm phase at low temperature for the samples with x ≤0.4. While the positive magnetodielectric effects can be attributed to a coupling of magnetic and crystallographic structures of the R3c phase, the observed negative magnetodielectric effect in the Pbnm phase can be associated with a low-temperature modification of the Pbnm structure. The observed dualsigned magnetodielectric effects suggest that the Bi1-xGdxFeO3 oxides are a good prototype for understanding the magnetodielectric coupling mechanism in this kind of materials.     

Pressure‐induced structural transformations in In2‐xYx(MoO4)3 systems

In this work, we report results of high‐pressure Raman experiments (P < 8 GPa) on In_2‐xY_xMo₃O₁₂ for x = 0.0 and 0.5. A crystalline to crystalline structural phase transition and pressure‐induced amorphization (PIA) have been identified. The structural phase transition takes place at 1.5 and 1.0 GPa for In₂(MoO₄)₃ and In_1.5Y_0.5(MoO₄)₃, respectively, resulting in the change of structure from monoclinic P2₁/a to a more denser structure. The PIA started at 5 and 3.4 GPa for In₂Mo₃O₁₂ and In_1.5Y_0.5Mo₃O₁₂, respectively. The amorphization process takes place in two stages in the case of In_1.5Y_0.5Mo₃O₁₂ phase, while for In₂Mo₃O₁₂, it is not complete until the pressure is as high as 7 GPa. Our results also suggest that with increase of ionic size of the A³⁺ ions, the octahedral distortion increases and consequently larger local structural disorder is introduced in the A₂(MoO₄)₃ system, where A is a trivalent ion (In, Y³⁺, Sc³⁺, Fe³⁺, etc.). Copyright © 2015 John Wiley & Sons, Ltd.     

新块材超导体Pr1-xCaxBa2Cu3O7-δ(0.4≤x≤0.6)的高压合成与超导电性

采用高温高压合成方法，合成出了Pr_1-xCa_xBa₂Cu₃O_7-δ(0.4≤x≤0.6) 系列块材超导体，在缺氧的Pr_0.5Ca_0.5Ba₂Cu₃O_7-δ四方123结构样品中得到了T_c为98K.实验结果表明Pr在123结构中的价态为大于3+的混合价态，因而空穴填充和杂化导致的载流子局域化是Pr抑制123相超导电性的关键因素. 关键词：     

The study of thermal expansion properties in solid solutions Ln2−xCrxMo3O12 (Ln=Ho and Lu) by high temperature X-ray diffraction

A systematic study of the formation, crystal structures and thermal expansion properties of solid solutions Ln_2?xCr_xMo₃O₁₂ (Ln=Ho and Lu) has been performed. Rietveld refinement results indicate that compounds Ho_2?xCr_xMo₃O₁₂ with 0≤x≤0.2 and Lu_2?xCr_xMo₃O₁₂ with 0≤x≤0.5 have orthorhombic structures and show negative thermal expansion in the temperature range of 200–800 °C. Compounds Ln_2?xCr_xMo₃O₁₂ with 1.7≤x≤2.0 have monoclinic structures and show strong positive thermal expansion in the temperature range of 25–300 °C. While compounds Ln_2?xCr_xMo₃O₁₂ with 1.7≤x≤2.0 adopt orthorhombic structures and show very low positive thermal expansion from 500 to 800 °C. Though the crystal structure plays the key rule in determining the thermal expansion properties, chemical composition and temperature also show important effect on the thermal expansion properties of these compounds.     

Tm3+/Yb3+共掺氟氧硅铝酸盐玻璃陶瓷蓝色上转换发光研究

按摩尔百分比制备了组分为30SiO₂-(20-x-y)Al₂O₃-40PbF₂-10CdF₂-xTm₂O₃-yYb₂O₃的两组Tm³⁺/Yb³⁺共掺杂氟氧硅铝酸盐上转换蓝色发光玻璃陶瓷材料,测量了其在980nm激 关键词： 玻璃陶瓷 上转换发光 3+/Yb³⁺掺杂')" href="#">Tm³⁺/Yb³⁺掺杂 掺杂浓度     

Co2+-Ti4+和Cu2+-Nb5+离子取代BaFe12O19单晶体中Fe3+离子的研究

本文对用Co²⁺-Ti⁴⁺和Cu²⁺-Nb⁵⁺离子取代BaFe₁₂O₁₉单晶体中Fe³⁺离子进行了研究,以Bi₂O₃作为助熔剂生长出了BaFe_12-2xCo_x²⁺Ti_x⁴⁺O₁₉(x=0;0.04;0.09;0.13;0.27和0.68)以及BaFe_12-x[Nb_1/3⁵⁺Cu_2/3²⁺]_xO₁₉(x=0;0.28;0.44和0.60)这两系列的单晶体,测定了100—300K温度范围内样品的磁化强度σ与单轴各向异性常数K₁,我们发现,对Co²⁺-Ti⁴⁺取代的样品,当x≤0.09时,其σ与K₁随x的增加而缓慢增加;当x>0.09时,其σ与K₁随x的增加而迅速降低,至x=1.1时,K₁变为零,对Nb⁵⁺-Cu²⁺取代的样品,其σ值在整个成份范围内基本保持不变,且有缓慢增加趋势;而K₁值则随x增加而单调下降,提出了取代离子在M型六角铁氧体中可能的分布模型来解释我们的结果。 关键词：     

Temperature‐dependent Raman scattering in ferroelectric Bi4−xNdxTi3O12(x = 0, 0.5, 0.85) single crystals

The temperature‐dependent Raman spectra of ferroelectric Bi_4−xNd_xTi₃O₁₂(x = 0, 0.5, 0.85) single crystals were recorded from 100 to 800 K. It was found that there is a critical Nd content x₀ between 0.5 and 0.85. The Nd³⁺ ions prefer to replace Bi³⁺ ions in pseudo‐perovskite layers when x < x₀, while they might begin to incorporate into (Bi₂O₂)²⁺ layers when x ≥ x₀. Nd substitution leads to a decrease in the ferroelectric–paraelectric transition temperature (T_c). A monoclinic distortion of orthorhombic structure occurs in Bi₄Ti₃O₁₂ crystals at temperatures below 200 K. Copyright © 2009 John Wiley & Sons, Ltd.     

Y1-xCaxBa2Cu3-xMxO7-δ (M=Fe,Ni)体系的超导电性

本文报道,通过对Y_1-xCa_xBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系样品的晶体结构、氧含量、正常态电阻率与温度的关系,以及超导转变温度等测量,并与YBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系进行比较,发现Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系的T_c显著地高于相应x值的YBa₂Cu_3-xFe_xO_7-δ体系,而Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系则相反,T_c低于仅Ni替代的体系,表明Ca和Fe同时替代时两者引起的载流子浓度(n_H)变化相互补偿,抑制了仅Fe替代时引起的n_H和T_c急剧下降;而作Ca和Ni同时替代时主要的不是两者引起载流子浓度变化的相互补偿,Ca和Ni替代效应之间的关联较弱。作者认为,对Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系属于CuO₂平面外的元素替代,这时载流子浓度是决定Tc的主要因素;而对Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系,由于Ni²⁺离子主要占据Cu(Ⅱ)位,它导致磁拆对效应,Ni²⁺离子的拆对效应是引起T_c下降的直接原因。 关键词：     

Gd3Ga5-xAlxO12单晶低温磁性的实验研究

采用提拉法制备了Gd₃Ga_5-xAl_xO₁₂(以下简称GGAG)单晶,经X射线粉末照相证实为石榴石型单相结构。在T=1.5—77K温区里,场强从45—60000Oe范围内,沿[111]晶轴方向测量了磁化强度和磁化率,并与本文所用钇镓石榴石Gd₃Ga₅O₁₂(以下简称GGG)和文献[1,2]报道的GGG单晶数据作了比较。实验结果表明:(1)在场强H<500Oe时,磁化率X与温度T的关系遵守居里-外斯定律,其有序温度T_N远低于1.5K;(2)H>10000Oe时,该材料的磁化强度(或磁化率)比GGG高3—4％;(3)在H～30000Oe时,特定温度T_min对应的临界场H_c比GGG约高4000Oe。实验研究表明,采用离子代换法寻找新的性能良好的磁致冷剂的途径是可行的。 关键词：     

Non-stoichiometric molybdenum oxides as cathodes for lithium cells. part v. thermodynamic,kinetic and structural aspects of the behaviour of Mo8O23 and Mo18O52

A deeper insight in the electrochemical behaviour of Li cells based on two non-stoichiometric Mo oxides, Mo₈O₂₃ and Mo₁₈O₅₂, was obtained by determining the OCV's, the diffusion coefficients and the variations of lattice parameters as a function of depth of discharge. The first material is a monoclinic framework-structured compound endowed with large channels which provide easy paths for Li⁺. Occupation of sites in the cavities of this structure produces at first a shrinkage of the unit cell, followed by a moderate re-expansion. Mo₁₈O₅₂ is a triclinic step-layered material which markedly expands upon Li⁺ intercalation. Li⁺ diffuses in it relatively slowly for x<1, i.e. before increasing the interlayer distance, and for x>0.4 due to coulombic repulsion between Li⁺ ions.