正交和四方YBa_2Cu_3O_(7-x)的热膨胀系数

用电容法测量了正交和四方YBa_2Cu_3O_(7-x)的热膨胀系数与温度的关系。结果表明,正交样品在205K附近,四方样品在92—130K之间热膨胀系数有异常。估计前者可能与晶格的不稳定性有关,说明具有较强的电-声子相互作用,后者可能与结构转变有关,因此破坏了高温超导电性。同时也发现正交样品在92K热膨胀系数有微小跳跃。由此估计了压力效应。     

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Eu_0.5Sr_0.5MnO₃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 关键词： 多相竞争 半掺杂 铁磁团簇     

钙钛矿（La1-yTby)0.67Sr0.33MnO3的磁致伸缩效应

采用固相反应烧结法制备了（La_1-yTb_y)_0.67Sr_0.33MnO₃系列样品（y=0,0.05,0.15,0.20,0.25,0.33,0.40,0.50,0.60,1.00).X射线衍射表明,随着y值增大钙钛矿型晶体结构从菱面对称性向正交对称性转变.180K时,μ₀H=7T条件下,在y=0.40样品的巨磁电阻可达900％.μ₀H=1.7T时,y=0.20样品的室温磁致伸缩为-50×10^-6.210K时,y=0.33样品的磁致伸缩可达-130×10^-6. 关键词：     

Nd0.5Sr0.4Pb0.1MnO3的结构和磁性

通过室温下的中子衍射和磁性测量对多晶样品Nd_0.5Sr_0.4Pb_{0 .1}MnO₃ 的结构和磁性进行了实验研究.中子衍射结果表明，该样品具有正交的钙钛矿结构，空间群 是Pnma，即结构发生了晶场畸变.由M-T和R-T曲线可知，居里温度T_C=273 K ，其特征是随着温度的增加样品经历了从铁磁金属态转变到顺磁半导态，且转变温度T _p＝225 K；用锰氧化物晶场和双交换作用的竞争解 关键词： 结构 磁性 中子衍射 晶场畸变 p')" href="#">转变温度T_p 双交换作用     

块体金属玻璃Zr46.75Ti8.25Cu7.5Ni10Be27.5的超导与负电阻温度系数

测量了块体金属玻璃Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5在退火前后其电阻值随温度的变化,测量的温度范围为1.5—300K.样品在退火前后都发现有超导现象.零磁场下其超导转变温度T_c分别为1.84和3.76K.在5—300K温度范围内,原始样品具有负的电阻温度系数.如果取Zr, Ti, Cu, Ni及Be分别贡献出1.5, 1.5, 0.5, 0.5及两个传导 关键词： 块体金属玻璃 超导 电阻温度系数     

(Lu,Y)2SiO5∶Ce3+与SrSO4∶Dy3+材料低温热释光及其测试仪器的研究

为了分析材料在低温下的陷阱能级,获得更多有关缺陷结构的信息,研制了一套由STM32微控制器为核心的低温热释光发光谱测量系统。设计了低温样品室,采用液氮冷却样品;STM32通过控制加热电流,实现样品以恒定速率升温,从而获得低温热释光发光曲线或三维热释光谱。温度测量范围为85~400 K,升温速率范围为0.1~10 K/s。设计了由STM32控制X射线及紫外光源的驱动电路,用于样品的激发。采用高灵敏度CCD实现对三维热释光谱的测量,采用单光子计数器获取二维热释光发光曲线。利用该系统测试了（Lu,Y）₂SiO₅:Ce³⁺（LYSO:Ce³⁺）单晶闪烁体与SrSO₄:Dy³⁺粉末样品的热释光谱及辐射发光光谱。观察到LYSO:Ce³⁺在108,200,380 K左右的热释光峰,发光波长位于390~450 nm之间,是明显的宽带峰。在低温下由于基质的自陷激子（STE）发射所形成的发射峰在166 K时发生猝灭。在309 K时,Ce³⁺发射峰展宽为单一发射峰;SrSO₄:Dy³⁺发光峰温度为178,385 K,发光波长由Dy³⁺离子的能级跃迁决定,在480,575,660,750 nm处呈现窄带发光峰。结果表明,系统人机交互界面友好,实验数据可靠,智能化程度高,操作简单。     

非晶态Fe13Ni67.2P4.5B15.3合金的临界现象

本文报道非晶态Fe₁₃Ni_67.2P_4.5B_15.3合金的磁化强度与温度和磁场关系的测量结果。在居里温度附近样品的磁特性符合二级相变规律,得到临界指数β=0.39±0.02,γ=1.56±0.06,δ=5.20±0.1,样品的居里温度T_c=(180.4±0.2)K。在实验误差范围内,临界指数β,γ,δ满足γ=β(δ-1)关系,在168—192K温度范围,实验数据满足二级相变的磁状态方程。当T>270K时,样品顺磁磁化率服从居里-外斯定律,由居里-外斯常数c计算出有效顺磁磁矩P_eff=3.19 μ_B。 关键词：     

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     

A3C60超导体的研究

 1991年5月,Bell实验室的A.F.Hebard等人首次在掺钾的C₆₀中观察到高达18K的超导电性.于是,这项研究结果在全世界掀起广泛的研究热潮,成为近年高温超导研究领域中又一热点.本文扼要介绍C₆₀掺杂实验的物性测量结果,引起C₆₀超导的几种可能机制及对C₆₀掺杂研究的意义.一、A_xC₆₀的掺杂实验及物性测量结果Hebard等人发现掺钾的C₆₀高达18K的超导电性是在9GHz频率下,用微波损耗测量样品的电阻率随温度的变化时观察到的.当样品冷却到约20K时,电阻率略有增加,后又降低,直到5K时电阻率降为零.超导转变宽度为4.6K,4K时临界电流密度为40A/cm².用SQUID磁强计测量证明了它的超导转变为18K.     

Bi2Sr2CaCu2O8单晶中的反常尖锋效应

使用牛津震动样品磁强计(VSM)研究了Bi₂Sr₂CaCu₂O₈单晶的磁滞回线.在20到40K温度之间发现了反常的尖锋效应,随样品O含量的增加,发生尖锋效应的外场也相应提高.可以认为在尖峰效应处发生了由涡漩物质的有序固态到无序固态的相变,在有少量点缺陷存在的BSCCO单晶相图上,B_sp线终止于20K温度处,在20K以下温区没有发生准格子到涡漩玻璃的相变,涡漩固相始终以准格子形式存在;可以认为尖峰效 关键词： 2Sr₂CaCu₂O₈单晶')" href="#">Bi₂Sr₂CaCu₂O₈单晶 磁滞回线 尖锋效应 相变     

PREPARATION, SUPERCONDUCTIVITY AND STRUCTURE OF THE LaBaCaCu3O7-x SUPERCONDUCTORS WITH Tc HIGHER THAN 80 K

In this paper, the preparation process of the tetragonal LaBaCaCu₃O_7-x (LBCCO) superconductor with T_c=84 K is repored. The superconductivity and structure of the LBCCO superconducting phase are investigated by means of X-ray diffraction (XRD), transmission electron microscope(TEM) and superconductivity measurements, The results indicate that the superconducting phase with T_c=82K in the LBCCO system has a tetragonal structure with a=0.3966nm, c=l.1838nm and space group P4/mmm. About 50% of the Ca and La atoms are located in 1d sites (i.e. Y site in the YBCO structure). It is confirmed that there is in fact no orthorhombic to tetragonal transition in this material. The relationship between the oxygen content and T_c is also presented.     

(Pb0.97La0.02)(Zr0.65Sn0.35-xTi x)O3反铁电陶瓷的热膨胀性质

在-100—200℃温度范围内，测量了(Pb_0.97La_0.02)(Zr_{0.65< /sub>Sn0.35-xTix)O3(PZST，0.1≤x≤0.14)反铁电陶 瓷的热膨胀性质.实验结果表明，组分在0.1 ≤x≤0.12的试样室温下为反铁电(AFEt)四方相，热膨胀系数(α)在低温段发生 “弯曲” ，而变温x射线衍射谱(XRD)显示材料保持四方相结构；当Ti含量在0.125≤x≤0.14时，室温 下是铁电三方相(FER)，温度升高时FER→AFEt相变体 积收缩，AFEt→立方顺电(PE c)相变体积增大；变温XRD谱证明了材料相结构随温度的转变过程.用多元复杂 化合物存在 纳米线度组分非均匀的观点解释了热膨胀性质随Ti含量演化的物理机理，并得到了该系统的 温度-Ti(x)含量相图. 关键词： 热膨胀性质 铁电/反铁电相界 反铁电陶瓷 PZST}     

Structures and phase transition in Rb2NaHoF6

The phase transition at T_c=172(2) K and high as well as the low temperature structures at 205 K and 17 K were studied with a low temperature Guinier diffractometer and camera. A second order phase transition (Γ-condensation of the T_1g mode) lowers the symmetry from Fm3m at T>;T_c to I4/m at T<T_c. In the low temperature phase the octahedra are tilted (5.2 degrees at 17 K) and slightly stretched. The increase of the tilt angle and the linear increase of the tetragonal distortion suggests a mean field power law. This classical behaviour would agree with the assumption of a Jahn Teller splitting of the Ho³⁺ electronic state.     

The effect of oxygen plasma generated by different microwave modes on NdBa2Cu3O6+δ superconductor: structure and IR studies

The effect of longitudinal and transverse modes of oxygen plasma generated by microwave source with frequency 2.45 GHz has been used to characterize polycrystalline samples of NdBa₂Cu₃O_6+δ (Nd-123) high T_c-superconductor. For this purpose we have developed a simple oxidation technique, used by us earlier, to investigate the effect of different modes on the appearance of superconductivity in Nd-123. Our main results show that the mode of microwave plasma and time of exposure can control the local arrangement of oxygen vacancies in CuO_δ basal plane. Samples exposed to the transverse mode reveals a well ordered orthorhombic phase transition while the longitudinal modes caused the samples to have a non-superconducting tetragonal structure for all of the exposure time. The T_c vs. δ curve does not show the typical 60 K plateau corresponding to the ortho-II phase. The IR spectrum show bands at shorter wavelengths which corresponding to the metal oxides.     

The heat capacity of the layer compounds (CH3CH2CH2NH3)2MnCl4 and (CH3CH2CH2NH3)2CdCl4 from 10 K TO 300 K

The heat capacity of the layer compounds tetrachlorobis (n-propylammonium) manganese II and tetrachlorobis (n-propylammonium) cadmium II, (CH₃CH₂CH₂NH₃)₂MnCl₄ and (CH₃CH₂CH₂NH₃)₂CdCl₄ respectively, has been measured over the temperature range 10 K ?T ? 300 K.Two known structural phase transitions were observed for the Mn compound in this temperature region: at T = 112.8 ± 0.1 K (ΔH_t= 586 ± 2 J mol^?1; ΔS_t = 5.47 ± 0.02 J K^?1mol^?1) and at T =164.3 ± (ΔH_t = 496 ± 7 J mol^?1; ΔS_t =3.29 ± 0.05 J K^?1mol^?1). The lower transition is known to be from a monoclinic structure to a tetragonal structure, while the upper is from the tetragonal phase to an orthorhombic one. From comparison with the results for the corresponding methyl Mn compound it is deduced that the lower transition primarily involves changes in H-bonding while the upper transition involves motion in the propyl chain.A new structural phase transition was observed in the Cd compound at T= 105.5 ± 0.1 K (ΔH_t= 1472.3 ± 0.1 J mol^?1; ΔS_t = 13.956 ± 0.001 J K^?1mol^?1), in addition to two transitions that have been observed previously by other techniques. The higher of these transitions(T = 178.7 ± 0.3 K; ΔH_t = 982 ± 4 J mol^?1 ΔS_t = 6.16 ± 0.02 J K^? mol^?1) is known to be between two orthorhombic structures, while the structural changes at the lower transition (T= 156.8 ± 0.2 K; ΔH_t = 598 ± 5 J mol^?1, ΔS_t = 3.85 ± 0.03 J K^?1 mol^?1) and at the new transition are not known. It is proposed that these two transitions correspond respectively to the tetragonal to orthorhombic and monoclinic to tetragonal transitions in the propyl Mn compounds.In addition to the structural phase transitions (CH₃CH₂CH₂NH₃)₂MnCl₄ magnetically orders at t? 130 K. The magnetic contribution to the heat capacity is deduced from the heat capacity of the corresponding diamagnetic Cd compound and is of the form expected for a quasi 2-dimensional Heisenberg antiferromagnet.     

Optical properties of CH3NH3PbI3 crystal grown using inverse temperature crystallization

Perovskite CH₃NH₃PbI₃ (MAPbI₃) single crystal was grown using inverse temperature crystallization method. Crystallinity of the perovskite was confirmed by X-ray diffraction. Photoluminescence (PL) spectra revealed abnormal behavior due to a temperature-induced orthorhombic to the tetragonal phase transition. Four PL emission peaks, A, B, C, and D, were observed in the low temperature regime. Peaks A and B were observed at 756 and 776?nm?at 12?K, and were blue-shifted and disappeared at 130 and 70?K, respectively. Peaks C and D were observed at 789 and 807?nm?at 40?K and were also blue-shifted to 780 and 794?nm?at 100?K. On the other hand, the peak C red-shifted to 799?nm from 100 to 140?K because of an orthorhombic to the tetragonal phase change and was also blue-shifted above 140?K. From the excitation intensity- and temperature-dependent PL results, peaks A and B were assigned to the free-exciton and bound-exciton of the orthorhombic phase crystal, respectively. In addition, peaks C and D were associated with the free-exciton and bound-exciton of the tetragonal phase crystal, respectively. The activation energy of peak C was calculated to be 98?meV from temperature dependence of the PL intensity.     

铌酸钾钠基无铅压电陶瓷的X射线衍射与相变分析

分析了斜方相、四方相铌酸钾钠基无铅压电陶瓷材料的结构和X射线衍射图谱的特点. 对于铌酸钾钠基压电材料斜方相结构, 从构成晶胞的一个单斜原胞进行分析, 计算出X射线衍射谱上每个衍射角附近的衍射峰数目和相对强度. 提出了2θ在20°—60°范围内根据(1 0 2)衍射峰(52°附近)和(1 2 1)衍射峰(57°附近)劈裂的数目区分斜方和四方相的新方法. 对于多晶陶瓷粉末, 可以更简便的由22°(或45°)附近前后峰的相对高低来判断斜方、四方相. 关键词： 铌酸钾钠 无铅压电陶瓷 X射线衍射 相变     

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.     

(Bi,Pb)2Sr2Ca2Cu3Oy单相样品的超导电性与载流子浓度

对(Bi,Pb)₂Sr₂Ca₂Cu₃O_y单相样品进行不同条件下的热处理,通过X射线衍射、电阻-温度关系、交流磁化率,以及Hall系数等测量,发现样品均具有较好的单相性,随着热处理条件的变化,其超导转变中点温度(T_c)有规律地分布在100—110K之间,T_c随载流子浓度(n_H)的增加而升高。实验结果表明,热处理条件对样品的相结构、超导 关键词：     

Orthorhombic structure: a necessity in superconducting 1-2-3 compounds

X-ray and resistivity measurements on YBa₂Cu₃O_7−δ (1-2-3) samples show that for the same but low oxygen concentration,δ⋍0·55, no superconducting transition down to 4·2 K is observed for the tetragonal phase samples while the orthorhombic phase shows aT _c ∼ 31 K. The effect of oxygen concentration onT _c is isolated.T _c=91±1 K has, however, been observed continuously for the normal oxygen annealed samples,δ⋍0·07. The experimental results suggest strongly the necessity of the 1-2-3 compound to be in the orthorhombic phase for the superconducting mechanism to be operative.