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）（...     

High-Q microwave dielectrics in the (Mg1−xZnx)Al2O4 (x = 0-0.1) system

The microwave dielectric properties and the microstructures of (Mg_1−xZn_x)Al₂O₄ (x = 0-0.1) ceramic system prepared by the conventional solid-state route were investigated. The forming of spinel-structured (Mg_1−xZn_x)Al₂O₄ (x = 0-0.1) solid solutions was confirmed by the XRD patterns and the measured lattice parameters, which linearly varied from a = b = c = 8.0815 Å for MgAl₂O₄ to a = b = c= 8.0828 Å for (Mg_0.9Zn_0.1)Al₂O₄. By increasing x, the Q × f of (Mg_1−xZn_x)Al₂O₄ can be tremendously boosted from 82,000 GHz at x = 0 to a maximum of 156,000 GHz at x = 0.05. The Zn substitution was effective in reducing the dielectric loss without detrimental effects on the ?_r and τ_f values of the ceramics.     

Low-firable high-K dielectric in the Zrx(Zn1/3Nb2/3)1−xTiO4 ceramic system

Composite ceramics in the solid solution of Zr_x(Zn_1/3Nb_2/3)_1−xTiO₄ (x = 0.1-0.4) have been prepared by the mixed oxide route. Formation of solid solution was confirmed by the X-ray diffraction patterns. The microwave dielectric properties, such as dielectric constant (?_r), Q × f value and temperature coefficient of resonant frequency (τ_f) have been investigated as a function of composition and sintering temperature. With x increasing from 0.1 to 0.4, the dielectric constant decreases from 70.9 to 43.2, and the τ_f decreases from 105 to 55 ppm/°C. The Q × f value, however, increases with increasing x value to a maximum 26,600 GHz (at 6 GHz) at x = 0.3, and then decreases thereafter. For low-loss microwave applications, a new microwave dielectric material Zr_0.3(Zn_1/3Nb_2/3)_0.7TiO₄, possessing a fine combination of microwave dielectric properties with a high ?_r of 51, a high Q × f of 26,600 GHz (at 6 GHz) and a τ_f of 70 ppm/°C, is suggested.     

High-dielectric-constant and low-loss microwave dielectric in the (1 − x)La(Mg0.5Ti0.5)O3-x(Ca0.8Sr0.2)TiO3 solid solution system

The microwave dielectric properties and microstructures of (1 − x)La(Mg_0.5Ti_0.5)O₃-x(Ca_0.8Sr_0.2)TiO₃ ceramics, prepared by a mixed oxide route, have been investigated. The forming of solid solutions was confirmed by the XRD patterns and the measured lattice parameters for all compositions. A near zero τ_f was achieved for samples with x = 0.5, although the dielectric properties varied with sintering temperature. The Q × f value of 0.5La(Mg_0.5Ti_0.5)O₃-0.5(Ca_0.8Sr_0.2)TiO₃ increased up to 1475 °C, after which it decreased. The decrease in dielectric properties was coincident with the onset of rapid grain growth. The optimum combination of microwave dielectric properties was achieved at 1475 °C for samples where x = 0.5 with a dielectric constant ?_r of 47.12, a Q × f value of 35,000 GHz (measured at 6.2 GHz) and a τ_f value of −4.7 ppm/°C.     

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.     

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...     

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).     

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。     

Phase evolution and microwave dielectric properties of TiO2-modified (Mg0.95Co0.05)2TiO4 ceramics

Phase evolution and microwave dielectric properties of (1 − x)(Mg_0.95Co_0.05)₂TiO₄-xTiO₂ (x = 0-1) ceramics prepared by the conventional mixed oxide route have been investigated. Increasing the TiO₂ content would lead to a main phase transformation from (Mg_0.95Co_0.05)₂TiO₄ to (Mg_0.95Co_0.05)TiO₃, (Mg_0.95Co_0.05)Ti₂O₅ and then TiO₂. Not only did the TiO₂ addition compensate the τ_f, it also lowered the sintering temperature of specimen. A huge drop of Q × f occurs at a 40-60 mol% TiO₂ addition was attributed to the formation of (Mg_0.95Co_0.05)Ti₂O₅ phase. Specimen with x = 0.78 can possess an excellent combination of microwave dielectric properties: ?_r ∼ 24.77, Q × f ∼ 38,500 GHz and τ_f ∼ −1.3 ppm/°C.     

Effect of CaTiO3 addition on microwave dielectric properties of Mg2(Ti0.95Sn0.05)O4 ceramics

The microwave dielectric properties of CaTiO₃-added Mg₂(Ti_0.95Sn_0.05)O₄ ceramics prepared by the mixed oxide route have been investigated. The combination of spinel-structured Mg₂(Ti_0.95Sn_0.05)O₄ and perovskite-structured CaTiO₃ forms a two-phase system (1 − x)Mg₂(Ti_0.95Sn_0.05)O₄-xCaTiO₃, which was confirmed by the XRD patterns and the EDX analysis and it also leads to a zero τ_f. The microwave dielectric properties of the ceramics can be effectively controlled by varying the x value. For practical applications, a new microwave dielectric material 0.91Mg₂(Ti_0.95Sn_0.05)O₄-0.09CaTiO₃ is suggested and it possesses a good combination of dielectric properties with an ?_r of ∼18.01, a Q × f of ∼92,000 GHz, and a τ_f of ∼0 ppm/°C, which makes it is a very promising candidate material for high frequency applications.     

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.     

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.     

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.     

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.     

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.     

The effect of non-stoichiometry on the microstructure and microwave dielectric properties of the Mg1+δTiO3+δ ceramics

The microwave dielectric properties and microstructure of Mg_1+δTiO_3+δ (−0.05 ≤ δ ≤ 0.05) ceramics prepared via the conventional solid-state route were investigated. A slight deviation from stoichiometry does not practically affect the relative permittivity and temperature coefficient of resonant frequency of the specimen. However, the Q × f value is very sensitive to the composition and it shows a non-linear variation corresponding to a relative amount of Mg. A very high Q × f can be achieved for specimen with single MgTiO₃ phase, which can be obtained within the compositional range −0.02 ≤ δ ≤ 0.02. In addition, a low Q × f measured for specimens at δ < −0.02 can be attributed to the presence of second phase MgTi₂O₅. An extremely high Q × f of ∼357,600 GHz (at 10 GHz) together with an ?_r of ∼18.3 and a τ_f of ∼−50 ppm/°C can be found for specimen using Mg_1.02TiO_3.02.     

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。     

Solvents for growing Al2(WO4)3 single crystals from high-temperature solutions

The crystallization conditions of Al₂(WO₄)₃ from Li₂O–WO₃ solvents (molar ratio 30.0:70.0, 32.5:67.5, 35.0:65.0, 45.0:55.0 and 55.0:45.0) as well as from Na₂O–WO₃ solvents (molar ratio 25.0:75.0, 27.5:72.5, 30.0:70.0 and 32.5:67.5) have been investigated. The concentration and temperature regions of crystallization of Al₂(WO₄)₃ and the density, viscosity as well as the solution losses due to evaporation have been established. On the basis of the data obtained it has been concluded that the most suitable solvent for growing Al₂(WO₄)₃ single crystals is Na₂O–WO₃ with a molar ratio of 27.5:72.5.