MnxCd1-xIn2 Te4晶体生长研究

采用Bridgman法生长四元稀磁化合物半导体Mn0.22Cd0.78In2Te4晶体。当晶体生长到预定长度时，淬火得到固液界面。采用光学显微镜、扫描电镜、X射线衍射仪、ISIS能谱仪以及Leica定量金相分析仪研究了晶体中出现的界面形态、相的和数量以及沿生长方向的相析出规律，并进行了相成分分析。研究发现，淬火得到的Mn0.22Cd0.78In2Te4晶体中存在两个界面，其中一个为固液相变界面，另一个为由α＋β两相区发展到单相β区时的转变界面，二者相对于生长初始端均为凹形；α＋β两相区中，β相以条状、花状和近似圆片状形式存在，其中条状β相多分布在晶界处；越接近生长初始端，花状和近似圆片状β相越小，条状β相越细，它们的含量越少；X射线衍射图谱表明，β相为黄铜矿结构，α相为面心立方结构。     

Structural and electrical properties of layered tetradymite-like compounds in the GeTe—Bi2Te3 and GeTe—Sb2Te3 systems

Analysis of the available crystallographic data shows that the GeTe-Bi₂Te₃ and GeTe-Sb₂Te₃ pseudobinary systems contain a wide variety of many-layered, long-period compounds belonging to the nGeTe · mBi₂Te₃ and nGeTe · mSb₂Te₃ homologous series. The Hall coefficient, thermoelectric power, and electrical conductivity of some of these compounds were measured over a wide temperature range. The temperature-dependent carrier mobility data suggest that both acoustic phonons and point defects contribute to the scattering of charge carriers. The lattice thermal conductivity of the many-layered, long-period compounds studied, κ_ph = 6–8 mW/(cm K), is notably lower than that of the constituent tellurides     

Electrical and microstructural properties of Bi2−x Sb x Te and Bi2−x Sb x Te2 foils obtained by the ultrarapid quenching process

This paper is concerned with the feasibility and reproducibility of the ultrarapid quenching process used to fabricate Bi_2–x Sb _x Te and Bi_2–x Sb _x Te₂ alloys for thermoelectric applications. Microstructural properties of the materials, obtained in the shape of foils, were studied concerning the phase analysis, cell parameters, texture, and microstructure observations. The Bi_2–x Sb _x Te alloys were found to have the (2 0 3) texture. The (2 0 4) texture, with an additional (1 1 0) component for x values greater than 0.4, was predominant for Bi_2–x Sb _x Te₂ foils. The electrical properties of these materials were then characterized by measuring the Seebeck coefficient, Hall coefficient, and electrical resistivity. It was found that Bi_2–x Sb _x Te foils changed from n- to p-type for an x-value of about 1.2. A maximum Seebeck coefficient, ||, of 36×10^–6 V K^–1 was measured for Bi₂Te. In the case of Bi_2–x Sb _x Te₂ foils, the change from n- to p-type was observed for an x value of about 1. A maximum Seebeck coefficient, ||, of 32×10^–6 V K^–1, was measured for Bi_1.4Sb_0.6Te₂. Measurements of the temperature-dependent electrical resistivity, Hall and Seebeck coefficients of the foils were carried out and the analysis revealed a semi-metallic behavior.     

GeSb2Te4薄膜表面形貌及力学性能的分形表征

以不同溅射功率在Si（111）基底上制备了GeSb2Te4薄膜。用原子力显微镜和X射线衍射仪以及高度相关函数法分析了薄膜生长表面形貌的分形维，并用纳米硬度计研究了薄膜表面的力学性能。结果表明，随着溅射功率增大，薄膜表面质量提高，分形维增大，且硬度和弹性上升；但超过一定值后，薄膜表面质量又会降低，分形维也随之减小，硬度和弹性下降。并指出借助分形维数可以优化溅射工艺参数，并能够较好地表征薄膜表面力学性能。     

Preparation and Magnetic Properties of InTe–Cr2Te3 Alloys

InTe–Cr₂Te₃ alloys were prepared and characterized by temperature-dependent magnetic measurements. The results lend support to earlier phase-diagram data indicating the formation of compounds with the compositions In₉Cr₂Te₁₂ and In₂Cr₆Te₁₁. In₉Cr₂Te₁₂ is shown to be a ferromagnet, while In₂Cr₆Te₁₁ has a more complex magnetic structure.     

Effect of Te Doping on the Structure and Superconductivity of K x Fe2−y Se2−z Te z Single Crystals

We report the structure, transport, and magnetic properties of K _x Fe_2?y Se_2?z Te _z single crystals grown by optical floating zone technique. The phase separation phenomena were observed in the Te-doped samples. With increasing Te doping level, the c-axis lattice parameter expands for both insulating/semiconducting and superconducting phases while the superconducting transition temperature (T _c) decreases and eventually vanishes at z = 0.51. The critical current density was estimated to be 10³–10⁴ A/cm² for the all doped samples. The upper critical field and anisotropic superconducting ratio increase with Te doping. We compared the results of critical current density J _c, upper critical field μ ₀ H _c2 and apparent thermally activated energy U ₀ for the samples with z = 0, 0.09, and 0.16. The influence of Te doping on the vortex pinning and the implication of U ₀ versus μ ₀ H is discussed.     

放电等离子烧结制备的Bi2Te3／Sb2Te3复合材料的热电性能

研究了用低温湿化学法和水热法制备纳米级的Bi2Te3和sb挪e3颗粒，并通过透射电镜观察其微观形貌。Bi2Te3粉末的微观形貌为直径在30-50n之间的片状小颗粒，而sb2Te3颗粒的微观形貌为薄带状，直径约为70nm，长度则为从150-300nm不等，并对其晶体的形核和长大机理进行了讨论。认为，纳米小颗粒状的Bi2Te3晶体可能是通过“表面形核和侧向生长”形成的产物，而薄带状的sb2Te3晶体可能是在Te块解体形成的条带状碎屑基础上形成的。用放电等离子烧结法（spark plasma sintering）制备不同比例的Bi2Te3／Sb2Te3块状复合材料，测量并比较了其热电性能。通过改变Bi2Te3的量，可以提高复合材料的电性能。成分不同的层片间的散射，能更有效地降低块体材料的热导率。在500K的温度下，Bi2Te3和sb2Te3以摩尔比为1：1复合烧结的试样的热导率低达0．7W／（m·K）。进一步优化Bi2Te3和sb2Te3的复合比例，其热电性能可能会有进一步的提高。     

[Mn(en)3]2·Sn2Se4Te2的结构和光吸收性能

按照K2Se:K2Te2:MnCl2@4H2O:SnCl2 2H2O:Se:乙二胺(en)＝3.8:1:2:2:6:270的摩尔比配料,采用溶剂热法使原料混合物在180℃反应7 d,得到黑色块状晶体[Mn(en)3]2@Sn2Se4Te2.属于三斜晶系,空间群为P-1,晶胞参数a＝0.91428(7)nm,b＝1.02781(7)nm,c＝1.15745(8)nm,α＝94.632(2)°,β＝100.944(2)°,γ＝115.918(1)°,V＝0.94382(12)nm3,Z＝1.晶体由[Mn(en)3]2+和(Sn2Se4Te2)4-堆积而成.具有Zintl结构的特征半导体[Mn(en)3]2@Sn2Se4Te2的光学能隙(Eg)为2.2 eV.当温度低于190℃时,[Mn(en)3]2@Sn2Se4Te2晶体是稳定的.详细讨论了这类化合物的组成对晶体结构和光吸收性能的影响.     

Composition Distribution in the MnxCd1-xIn2Te4 Ingot Grown by ACRT-B Method

MnxCd1-xIn2Te4 (x=0.1) ingot was successfully grown by the modified Bridgman technique, which applied the accelerated crucible rotation technique (ACRT) in Bridgman process, or briefly ACRT-B. The growth interface profile shape and the composition distribution in the MnxCd1-xIn2Te4 (x=0.1) ingot were analyzed. Even though the stoichiometric composition was synthesized in the original ingot, the composition has been redistributed during the ACRT-B growth process. Mn and Cd contents decrease while In increases along the longitudinal axis. The partition ratios of solutes Mn, Cd and In at the growth interface are evaluated by a mathematical method based on the experimental data, which are found to be 1.286, 1.926 and 0.729 in α phase growth process, and 1.120, 1.055 and 0.985 in β phase growth process, respectively. In the radial direction,Mn and Cd contents increase while In decreases with the distance from the centerline of the ingot.     

Composition and Properties of Layered Compounds in the GeTe–Sb2Te3System

The 620-K section of the Ge–Sb–Te phase diagram was mapped out using x-ray diffraction, microstructural analysis, and microhardness measurements. The transport properties of the layered tetradymite-like compounds nGeTe · mSb₂Te₃(n, m= 1–4) were studied in wide temperature ranges (Hall effect and electrical resistivity, from 77 to 800 K, and thermoelectric power, from 90 to 450 K). The results show that the nGeTe · mSb₂Te₃compounds are degeneratep-type semiconductors with a fairly high hole concentration due to the high density of intrinsic point defects. The temperature dependences of the Hall coefficient and resistivity exhibit anomalies related to solid-state phase transitions. The room-temperature lattice thermal conductivity ofnGeTe · mSb₂Te₃is fairly low, in the range 8–10 mW/(cm K).     

ACRT-B法生长的MnxCd1-xIn2Te4晶体的溶质分凝特性

研究了ACRT－B法生长的Mn0.2Cd0.9In2Te4晶体中界面形状和各组元沿轴向的分布规律及其分凝因数，发现结晶界面为椭球形；采用理想配比生长MnxCd1-xIn2Te4晶体，其4种组元并不按（Mn,Cd):In:Te=1:2:4比例结晶，而是要重新分布；通过数学方法处理实验数据得到Mn,Cd,In的分凝因数在α相区分别为1．286，1．9257和0．7294，在β相区则分别为1．12，1．055和0．985。     

Phase equilibria in the reciprocal system 3Tl2S + Bi2Te3 ↔ 3Tl2Te + Bi2S3

Phase equilibria in the reciprocal system 3Tl₂S + Bi₂Te₃ ? 3Tl₂Te + Bi₂S₃ (A) have been studied by differential thermal analysis, X-ray diffraction, microhardness tests, and emf measurements using thallium concentration cells, and a number of vertical sections, the 300-K isothermal section of its phase diagram, and the liquidus projection have been mapped out. The system is shown to be reversibly reciprocal, with broad solid solution regions in the Tl₂S-Tl₂Te-Tl₉BiTe₆ subsystem and along the TlBiS₂-TlBiTe₂ join. We have determined the homogeneity ranges and primary crystallization fields of the phases and identified the nature and coordinates of invariant equilibria in system A.     

The growth and properties of (Sbx Bi1–x)2Te3 crystals

Abstract

Vertical Bridgman systems with programmable temperature control are used to grow (Sb_xBi_1:x)₂Te₃ crystals. High purity Bi, Sb and Te are used as sources and the diameter of 1.1 cm, little soft bulk crystals of (Sb_xBi_1–x)₂ Te₃ can be obtained. Scanning electron microscope (SEM) and electron probe microanalysis (EPMA) are used to analyze the micro‐structure and the compositions of the crystal. From the X‐ray diffraction patterns it appears that the grown crystal is single crystal or directive polycrystal. If the uniformity of the source solution and grown temperature are under control, then the high quality of single crystals can be obtained. The dependence of crystal structure and the thermoelectric characteristics on the changed compositions of grown crystals are discussed. The optimum composition for the thermoelectric properties is Sb_1.00 Bi_1.04Te_2.96. When the DC current, 3A, is applied to the Sb_1.00 Bi_1.04 Te_2.96 crystal with suitable electrodes, the temperature difference (△T) between two sides of the crystal can be as high as 60°C. It is 2 times larger than that ever obtained by Sb₂Te₃ crystal. It appeared that the grown (Sb_xBi_1‐x)₂Te₃ crystals have the potential on the fabrication of thermoelectric devices and electronic cooling system.     

Ge2Sb2Te5相变存储器导电机制研究

本文研究了Ge2 Sb2 Te5相变存储器的导电机制.本文考虑了实验中观察到的场致激活能的非线性下降以及结晶化后跳跃间距变大带来的影响,提出了一种有效导带底偏移模型,并在此基础上建立了修正的电流模型.计算结果表明,激活能随电压增加呈双曲余切的下降趋势,符合测量结果.该模型还包含了温度效应,结果表明跳跃间距与温度成反比....     

Thermoelectric properties of Bi2Te3-Sb2Te3 single crystals in the range 100–700 K

The electrical conductivity, thermoelectric power, and thermal conductivity of Bi₂Te₃-Sb₂Te₃ crystals grown by the floating-crucible technique were measured in the temperature range from 100 to 700 K. The thermoelectric figure of merit of the crystals was evaluated. The effect of crystal composition on these properties was analyzed.     

CuCr2–xSbxS4 and Cu1–ySbyCr2S4 solid solutions

CuCr_2–ySb_xS₄ and Cu_1–ySb_yCr₂S₄ solid solutions with the spinel structure were synthesized, and their magnetic and electrical properties were studied. The limits of solid solutions in these systems were found to bex = 0.5 andy = 0.22. Models of the cation distributions in the solid solutions are proposed. The CuCr_2-xSb_xS₄ solid solutions with 0.10 <x < 0.15 are magnetic semiconductors with high ferromagnetic ordering temperatures.     

超声波-水热法合成Bi2Te3纳米管

以水为反应介质，NaBH4为还原剂，合成了BizTe3纳米管及纳米微粒。溶液首先在超声波发生器中预处理1h，然后置于150℃，水热反应釜中继续反应48h。XRD分析表明：合成产物主要物相为Bi2Te3；SEM观察可见产物中有纳米管生成，纳米管直径约为50-100nm，管壁厚约8-10nm，长度在500nm以上。EDS分析表明：纳米管成份为Bi2Te3。Bi2Te3纳米管可能的生长机制为纳米薄片-卷曲-闭合-纳米管。     

射频磁控溅射制备Bi2Te3热电薄膜

通过射频磁控溅射，在溅射气体为Ar，气压为1Pa，溅射功率为120W时分别在聚氨酯和玻璃基底上沉积了不同厚度的Bi2Te3薄膜。Bi2Te3薄膜主要是以（221）晶面平行于基底进行外延生长，先在基底形成大量微小晶粒，合并长大成典型的纤维状组织结构。在此条件下薄膜生长速率为26nm/min，通过控制溅射时间可沉积几纳米到几微米不同厚度的薄膜。得到的p-型半导体Bi2Te3薄膜，其电阻率随薄膜厚度的增大而减小。