Vertical Bridgman Seeded Growth of Cd_(1-x)Zn_xTe Crystals

ＶｅｒｔｉｃａｌＢｒｉｄｇｍａｎＳｅｅｄｅｄＧｒｏｗｔｈｏｆＣｄ＿（１－ｘ）Ｚｎ＿ｘＴｅＣｒｙｓｔａｌｓＨｏｕＱｉｎｇｒｕｎ；ＣｈｅｎＪｉ＇ａｎ；ＺｈａｏＬｅｍｉｎａｎｄＺｈａｎｇＸｉｎｍｉｎ（侯清润），（陈纪安），（赵乐敏），（张新敏）（Ｎｏｒｔｈ...     

MOCVD Growth of GaAs / Al_xGa_(1-x) As Superlattices

ＭＯＣＶＤＧｒｏｗｔｈｏｆＧａＡｓ／Ａｌ＿ｘＧａ＿（１－ｘ）ＡｓＳｕｐｅｒｌａｔｔｉｃｅｓＸｕＸｉａｎ＇ｇａｎｇ；ＨｕａｎｇＢａｉｂｉａｏ；ＲｅｎＨｏｎｇｗｅｎ；ＬｉｕＳｈｉｗｅｎａｎｄＪｉａｎｇＭｉｎｈｕａ（徐现刚）（黄柏标）（任红文）（刘士文）（...     

Molecular beam epitaxial growth of zinc-blende FeN(1 1 1) on wurtzite GaN(0 0 0 1)

We report a study of the growth of iron nitride on gallium nitride using molecular beam epitaxy with Fe e-beam evaporation and rf N-plasma growth. Thin iron nitride layers of thickness about 16 nm were grown and monitored in situ using reflection high energy electron diffraction. The samples following growth were analyzed ex situ using a variety of techniques including X-ray diffraction, Rutherford Backscattering, and atomic force microscopy. By monitoring the structure, morphology, and lattice constant evolution of the iron nitride film, the crystal phase and orientation with respect to the GaN substrate are deduced; and from RBS data, the stoichiometry is obtained. The growth is discussed in terms of a 2-D to 3-D growth mode transition, and a critical thickness is estimated.     

Single crystal preparation and crystal structure of the Cu2Zn/Cd,Hg/SnSe4 compounds

Single crystals of Cu₂Zn/Cd/SnSe₄ were grown using a solution-fusion method. The crystal structure of the Cu₂Zn/Cd,Hg/SnSe₄ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the stannite structure (space group I 2m) with the lattice parameters: a=0.56882(9), c=1.13378(9) nm, c/a=1.993 (Cu₂ZnSnSe₄), a=0.58337(2), c=1.14039(4) nm, c/a=1.955 (Cu₂CdSnSe₄) and a=0.58288(1), c=1.14179(2) nm, c/a=1.959 (Cu₂HgSnSe₄). Atomic parameters were refined in the isotropic approximation (R_I=0.0517, R_I=0.0511 and R_I=0.0695 for Cu₂ZnSnSe₄, Cu₂CdSnSe₄ and Cu₂HgSnSe₄, respectively).     

Growth of Ga_xIn_（1－x）Sb Alloys by MOCVD—Solid Composition Surface Morphology and Electrical Propert

ＧｒｏｗｔｈＯｆＧａ＿ｘＩｎ＿（１－ｘ）ＳｂＡｌｌｏｙｓｂｙＭＯＣＶＤ—ＳｏｌｉｄＣｏｍｐｏｓｉｔｉｏｎＳｕｒｆａｃｅＭｏｒｐｈｏｌｏｇｙａｎｄＥｌｅｃｔｒｉｃａｌＰｒｏｐｅｒｔｉｅｓＺｈａｎｇＢａｏｆｉｎ，ＺｈｏｕＴｉａｎｍｉｎｇ，ＪｉａｎｇＨｏｎ...     

La_(1-x/2)Pr_(1-x/2)Sr_xCuO_(4+y)的正常态电阻反常与超导电性

La1-x/2Pr1-x/2SrxCuOy(LPSCO)多晶样品采用传统的固相反应法制备。X射线衍射表明:LPSCO具有典型的空穴搀杂的T-214相的结构。磁化率测量显示:Sr掺杂在0.05≤x≤0.30范围内具有超导转变;Tc随x的增大呈抛物线形式变化,且在x=0.18时达到最大值28K。电阻的测量显示:随掺杂量的增大,系统呈现从绝缘到半导体,最后到金属的导电行为的变化;在欠掺杂区,正常态电阻温度关系符合ρ(T)=ρ0+αT-ClnT;而在过掺杂区,对数项消失。本文从替代所引起的晶体结构和载流子特性变化解释了Sr掺杂样品的输运行为和超导特性。     

Crystal structure and dielectric properties of La(Mg0.5Ti0.5)O3-Ca0.8Sm0.4/3TiO3 solid solution system at microwave frequencies

The crystal structure and the dielectric properties of (1 − x)La(Mg_0.5Ti_0.5)O₃-xCa_0.8Sm_0.4/3TiO₃ ceramics have been investigated. Ca_0.8Sm_0.4/3TiO₃ was employed as a τ_f compensator and was added to La(Mg_0.5Ti_0.5)O₃ to achieve a temperature-stable material. The formation of (1 − x)La(Mg_0.5Ti_0.5)O₃-xCa_0.8Sm_0.4/3TiO₃ solid solutions were confirmed by the XRD results and the measured lattice parameters for all compositions. The dielectric properties are strongly correlated to the sintering temperature and the compositional ratio of the specimens. Although the ?_r of the specimen could be boosted by increasing the amount of Ca_0.8Sm_0.4/3TiO₃, it would instead render a decrease in the Q × f. The τ_f value is strongly correlated to the compositions and can be controlled by the existing phases. A new microwave dielectric material 0.45La(Mg_0.5Ti_0.5)O₃-0.55Ca_0.8Sm_0.4/3TiO₃, possessing a fine combination of microwave dielectric properties with an ?_r of 47.83, a Q × f of 26,500 GHz (at 6.2 GHz) and a τ_f of −1.7 ppm/°C, is proposed as a very promising candidate material for today's 3G applications.     

Growth and annealing properties of Mg0.4Al2.4O4 crystal

Mg_0.4Al_2.4O₄ single crystals with good optical quality were successfully grown by the Czochralski method. The transmission spectrum indicated that the absorption edge of the crystal was at 220 nm, while no apparent absorption peaks were found. The X-ray diffraction and DSC curve analysis showed that Mg_0.4Al_2.4O₄ crystal was stable at room temperature. While after annealing in the air and hydrogen atmosphere at about 1200 °C, Mg_0.4Al_2.4O₄ decomposed into Al₂O₃ and (MgO)_0.4(Al₂O₃)_x (0.4 < x < 1.2). The reaction mainly occurred on the crystal surface, barely inside.     

Synthesis of novel compounds with cation ordered fluorite and α-PbO2 related structures by oxidation of Sn2Nb2O7 pyrochlore

Sn(II)_1.2(Nb(V)_1.6Sn(IV)_0.4)O₆ pyrochlore precursor was oxidized at temperature of the range 573–973 K in 1% O₂/Ar and O₂ gases for various periods of time. Two kinds of novel metastable phases with a composition of Sn(IV)_0.6(Nb(V)_0.8Sn(IV)_0.2)O_3.6 could be synthesized. Further, the other novel metastable phase with the same composition was found as a phase contained. One of the metastable phases was the cubic κ-CeZrO₄ related-type possessing the fluorite-related structure, which was formed by the cation diffusionless insertion of the oxygen atom into original oxygen vacant site of the pyrochlore-type structure. Another was an orthorhombic α-PbO₂ related-type possessing a cation ordered arrangement unlike a well known NiWO₄ structure. The other was the rutile related-type possessing a cation ordered arrangement. Appearance of the two latter metastable phases could be attributed to the displacement of the oxygen stacking in the κ-CeZrO₄ related-type phase without cation redistributions. The appearance mechanisms were analogous to the well known transformations for AX₂ compounds among rutile-type, α-PbO₂-type, and fluorite-type phases under high pressure and its release. The dependence of the appearance of these novel metastable phases on oxygen partial pressure and temperature has been discussed in terms of the driving forces and energy barriers for reactions.     

Thermal properties of Y_(1-x)Mg_xTaO_(4-x/2) ceramics via anion sublattice adjustment

A systematic investigation concerned with Y_(1-x)Mg_xTaO_(4-x/2)(x=0,0.08,0.12,0.16 and 0.20,respectively)ceramics was fabricated by a solid-state reaction method and characterized by X-ray diffraction(XRD),Raman spectroscopy,scanning electron microscopy(SEM)and thermal analysis.XRD spectra display that all of the samples are excellently consistent with the standard XRD spectrum of monoclinic YTaO_4(PDF No.24-1415;space group:I2(5)).The Raman peaks of the samples doped with Mg~(2+)just widen slightly compared with those of pure YTaO_4,which are in agreement with the results of XRD.The thermal conductivity of dense 7 wt%–8 wt%yttria-stabilized zirconia(7–8 YSZ)ceramic is about 2.5 W·m~(-1)·K~(-1)at 900°C,while the Y_(1-x)Mg_xTaO_(4-x/2)(x=0,0.08,0.12,0.16 and 0.20)ceramics possess lower thermal conductivity in the range of 1.45–1.57 W·m~(-1)·K~(-1)at 900°C,which declines by35%compared with that of 7–8 YSZ.The lower thermal conductivities of Y_(1-x)Mg_xTaO_(4-x/2)(x=0,0.08,0.12,0.16and 0.20)ceramics are originated from the enhanced phonon scattering caused by oxygen vacancy and Mg~(2+)ions defect complex.However,the thermal expansion coefficients are about 9.0 9 10~(-6)–9.5 9 10~(-6)K~(-1)along with the different amounts of Mg~(2+)doping at 1200°C.Compared to the pure sample,the thermal expansion coefficient decreases slightly when the Mg~(2+)doping amount is over 20%.The systematic investigations on the phase,microstructure,elastic and thermal properties of Y_(1-x)Mg_xTaO_(4-x/2)(x=0,0.08,0.12,0.16 and 0.20)ceramics will provide guidance for its application at high temperature,especially as thermal barrier coatings.     

Crystal growth and structure of La3MGa5O14 (M=Ti, Zr, Hf)

La₃M⁴⁺Ga₅O₁₄ (M=Ti, Zr, Hf) compounds were crystallized using the micro-pulling down and Czochralski techniques. Both growth methods showed that these three crystals are peritectic compounds. The structure of La₃TiGa₅O₁₄ (LTiG) crystal was refined using single-crystal X-ray diffraction data. LTiG was observed to be isostructural to Ca₃Ga₂Ge₄O₁₄ (P321 (No.150), Z=1) and the lattice parameters are a=8.223(1), c=5.109(1) Å. The Ti atoms were found to occupy octahedral (1a) and tetrahedral (3f) sites coordinated by six and four oxygen atoms, respectively.     

Growth of single crystals of Hg(BrxI1−x)2 and their detection capability

Hg(Br_xI_1−x)₂ crystals were grown by the Bridgman method for 0.2 < x < 1.0. They were tested for potential implementation as X- and γ-ray detectors at room temperature. ²⁴¹Am and ⁵⁵Fe were used as radioactive sources. From the corresponding energy spectra, it is evident that crystals with x = 0.2 show enhanced resolution at low energies (below 200 keV), competing those fabricated from HgI₂ and CdTe. Crystals with higher x's were of lower resolution.     

相场模型模拟强界面能各向异性作用下晶体生长

用Eggleston等提出的方案对界面能各向异性函数进行重整化处理,并使用相场模型对强各向异性情形下的晶体生长进行了模拟.在晶体平衡形态模拟中再现了晶向缺失现象,并与理论预测结果相一致.在自由枝晶生长过程中,当各向异性低于临界值时.枝晶生长速度随着各向异性系数增大而增大;在临界值附近生长速度突然降低5%;当高于临界值时生长速度又开始增加直到在0.20处达到最大值,其后基本不变.     

Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.     

Hydrothermal synthesis of superconductors Ba1−xKxBiO3 and double perovskites Ba1−xKxBi1−yNayO3

Superconductors Ba_1−xK_xBiO₃ and body-centered double perovskites Ba_1−xK_xBi_1−yNa_yO₃ have been selectively synthesized by a facile hydrothermal route. The appropriate ratio and adding sequence of initial reagents, alkalinity, reaction temperature and time are the critical factors that influence the crystal growth of the compounds. The purity and homogeneity of the crystals were detected by the ICP, SEM, EDX and TEM studies. Magnetic measurements show that the superconducting transition temperatures T_C of Ba_1−xK_xBiO₃ decrease from 22 K (for x = 0.35) to 8 K (for x = 0.55) with increasing the K doping level.     

Li_(1 2x)Zn_(1-x_PO_4的合成及其锂离子的导电性

以Li2 CO3,ZnO和NH4 H2 PO4 为原料 ,采用传统固相合成法和柠檬酸盐溶胶凝胶法制备了组成为Li1 2xZn1-xPO4 (x =0～ 0 .5 )的固体粉末和烧结体。对合成材料作了DTA ,TG ,XRD和SEM等分析 ,并用交流阻抗技术测定了样品的导电性。实验结果表明 ,与传统的固相合成方法相比 ,溶胶凝胶法可以使样品合成温度降低约 40 0℃ ,并且具有较高的导电率。     

溶胶凝胶法合成尖晶石型Li_(1 x)Mn_(2-x)O_4的工艺优化

通过引入水热合成对Pechini法进行改进 ,合成了锂离子正极材料Li1 xMn2 -xO4 。讨论了反应物的摩尔比、烧结温度、烧结时间和回火工艺对产物结构和粒度的影响。结果表明 ,烧结温度和时间以及Li/Mn摩尔比对产物的结构有较大影响 ,回火工艺可改善产物的粒度分布。优化的工艺条件为 :x =0 .0 6 ,烧结温度 6 5 0℃ ,烧结 6h ,再在 42 0℃回火 3h。得到的产物结构完整 ,颗粒均匀 ,放电容量为 118mAh/g。     

Crystal structure and magnetic properties of the new ternary actinide compounds AnPd5Al2 (An = U, Np)

We report the crystal structure and magnetic properties of new ternary actinide compounds UPd₅Al₂ and NpPd₅Al₂. Both compounds crystallize in the body-centered tetragonal ZrNi₂Al₅-type tetragonal structure (I 4/mmm). Although the magnetic susceptibility of both compounds follows the Curie–Weiss behavior at high temperature, no magnetic phase transition was observed. UPd₅Al₂ has a nonmagnetic ground state where the magnetic susceptibility saturates at low temperature, while NpPd₅Al₂ superconducts below 4.9 K as reported recently.     

Growth and characterization of epitaxial Ba(Zn1/3Ta2/3)O3 (1 0 0) thin films

We have synthesized and characterized epitaxial and stoichiometric Ba(Zn_1/3Ta_2/3)O₃ (1 0 0) dielectric thin films grown on MgO (1 0 0) substrates by pulsed laser deposition. Advanced electronic structure calculations were used to guide the interpretation of the experimental data. Zn-enriched targets and high oxygen pressures were used to compensate for Zn loss during film growth. The Ba(Zn_1/3Ta_2/3)O₃ films had an indirect optical band gap of ～3.0 eV and a refractive index of 1.91 in the visible spectral range. Zn–Ta B-site ordering was not observed in the Ba(Zn_1/3Ta_2/3)O₃ thin film X-ray diffraction data. A dielectric constant of 25 and dissipation factor of 0.0025 at 100 kHz were measured using the interdigital capacitor method. The Ba(Zn_1/3Ta_2/3)O₃ films exhibited a small thermally activated ohmic leakage current at high fields (<250 kV cm^–1) and high temperatures (<200 °C) with an activation energy of 0.85 eV.     

纳米Sr_(1-x)Ca_xTiO_3粉体制备及性能表征

采用改良的柠檬酸前驱体法制备纳米Sr_(1-x)Ca_xTiO_3(x=0.1, 0.2, 0.3, 0.4)粉体.借助于TG/DSC、XRD、TEM等表征手段对所得粉体的物相、形貌、颗粒尺寸进行了分析和测试.研究表明,经900 ℃煅烧7 h制备出的Sr_(1-x)Ca_xTiO_3粉体平均粒度为50 nm,结晶度高、形貌规整均一,并且无其它杂相.