Cation ordering and crystal structures in AGa2X4 compounds (CoGa2S4, CdGa2S4, CdGa2Se4, HgGa2Se4, HgGa2Te4)

Single crystals of some AGa₂X₄ compounds (CoGa₂S₄, CdGa₂S₄, CdGa₂Se₄, HgGa₂Se₄, HgGa₂Te₄) were prepared by chemical vapour deposition and flux method.The X-ray structural investigations indicated blende or defect chalcopyrite structures.A simple relationship is suggested between the c/a ratio and the cationic sublattice ordering.     

BaB2O4-K2O和BaB2O4-K2B2O4赝二元系相图的研究

用X射线衍射和差热分析方法研究了BaB₂O₄-K₂O和BaB₂O₄-K₂B₂O₄赝二元系的相平衡关系。BaB₂O₄-K₂B₂O₄属共晶体系,共晶温度为850±3℃,共晶点成分为45mol％K₂O。在Ba 关键词：     

Li2SO4—Li2B2O4,Li2SO4—(NH4)2SO4赝二元系相图及离子导电性研究

本文用差热分析和X射线衍射方法对Li₂SO₄-Li₂B₂O₄和Li₂SO₄-[NH₄]₂SO₄两个赝二元系相图进行了研究。Li₂SO₄-Li₂B₂O₄是共晶体系,共晶温度为720℃ 关键词：     

BaO-Li2O-B2O3三元系中BaB2O4-Li2B2O4和BaB2O4-Li2O截面相平衡关系的研究

本文用X射线和差热分析方法对BaO-Li₂O-B₂O₃三元系中的两个截面:BaB₂O₄-Li₂B₂O₄和BaB₂O₄-Li₂O作了研究。在BaB₂O₄-Li₂B₂O₄赝二元系中发现了一个新的化合物4BaB₂O₄·Li₂B₂O₄。化合物在930±3℃由包晶反应形成,并与Li₂B₂O₄形成共晶反应。共晶温度为797±3℃,共晶点组分为79mol％Li₂B₂O₄。在BaB₂O₄-Li₂O截面中也存在化合物4BaB₂O₄·Li₂B₂O₄,其包晶反应温度从930±3℃随Li₂O含量增加下降到908±3℃。在组分60mol％Li₂O处形成另一个新的化合物2BaB₂O₄·3Li₂O。该化合物在630±3℃也是由包晶反应形成,并与Li₂O和Li₂CO₃分别形成共晶反应,共晶温度分别为400±3℃和612±3℃。在BaB₂O₄-Li₂B₂O₄和BaB₂O₄-Li₂O体系中都没有观察到固溶体。用计算机程序分别对化合物4BaB₂O₄·Li₂B₂O₄和2BaB₂O₄·3Li₂O的X射线粉末衍射图案进行了指标化,其结果:4BaB₂O₄·Li₂B₂O₄的空间群为Pmma,a=13.033?,b=14.630?,c=4.247?,每个单胞包含两个化合式单位;2BaB₂O₄·3Li₂O的空间群为Pmmm,a=4.814?,b=9.897?,c=11.523?,每个单胞也含有两个化合式单位。 关键词：     

Luminescence characteristics of Eu2+ activated Ca2SiO4 Sr2SiO4 and Ba2SiO4 phosphorsfor white LEDs

<正>This paper investigates the luminescence characteristics of Eu²⁺ activated Ca₂SiO₄,Sr₂SiO₄ and Ba₂SiO₄ phosphors. Two emission bands are assigned to the f-d transitions of Eu²⁺ ions doped into two different cation sites in host lattices,and show different emission colour variation caused by substituting M²⁺ cations for smaller cations.This behaviour is discussed in terms of two competing factors of the crystal field strength and covalence.These phosphors with maximum excitation of around 370 nm can be applied as a colour-tunable phosphor for light-emitting diodes（LEDs） based on ultraviolet chip/phosphor technology.     

Immiscibility in the NiFe2O4-NiCr2O4 spinel binary

The solid solution behavior of the Ni(Fe_1−nCr_n)₂O₄ spinel binary is investigated in the temperature range 400-1200 °C. Non-ideal solution behavior, as exhibited by non-linear changes in lattice parameter with changes in n, is observed in a series of single-phase solids air-cooled from 1200 °C. Air-annealing for 1 year at 600 °C resulted in partial phase separation in a spinel binary having n=0.5. Spinel crystals grown from NiO, Fe₂O₃ and Cr₂O₃ reactants, mixed to give NiCrFeO₄, by Ostwald ripening in a molten salt solvent, exhibited single-phase stability down to about 750 °C (the estimated consolute solution temperature, T_cs). A solvus exists below T_cs. The solvus becomes increasingly asymmetric at lower temperatures and extrapolates to n values of 0.2 and 0.7 at 300 °C. The extrapolated solvus is shown to be consistent with that predicted using a primitive regular solution model in which free energies of mixing are determined entirely from changes in configurational entropy at room temperature.     

Non-isothermal decomposition of NiC2O4-FeC2O4 mixture aiming at the production of NiFe2O4

The non-isothermal decomposition of NiC₂O₄·2H₂O-FeC₂O₄·2H₂O (1:2 mole ratio) mixture was studied on heating to the formation of NiO-Fe₂O₃ mixture at 350 °C in air atmosphere using thermogravimetry. Kinetic analysis of data according to the integral composite method showed that the oxidative decomposition of FeC₂O₄ and NiC₂O₄ are best described by the three-dimensional phase boundary model. The activation parameters were calculated and discussed. The solid products at different decomposition stages were identified using XRD, Mössbauer and FT-IR spectroscopic techniques. Some characteristic XRD lines of NiFe₂O₄ start to appear at 800 °C beside the characteristic lines of NiO and Fe₂O₃, whereas at 1000 °C, only the characteristic lines of single phase cubic NiFe₂O₄ appeared. The Mössbauer spectrum at 1000 °C fitted into two Zeeman sextets characteristic of Fe³⁺ on the tetrahedral (A) and octahedral (B) sites of NiFe₂O₄ inverse spinel. Consistent results were obtained using FT-IR where the absorption bands appeared at 602 and 407 cm⁻¹ for the mixture calcined at 1000 °C. These can be assigned to the intrinsic vibrations of tetrahedral and octahedral sites of NiFe₂O₄, respectively.     

Dielectric properties of CsH2PO4 and CsD2PO4

Orthorhombic CsH₂PO₄ undergoes a ferroelectric transition at T_c = ?119.5°C, whereas the ferroelectric transition temperature in isomorphous CsD₂PO₄ is T_c = ?5.55°C. The transitions are of first order in both cases. The rather large isotope effect demonstrates the importance of the OHO bonds in the transition mechanism.     

Electrical properties of FeCr2S4 and CoCr2S4

Resistivity and magnetoresistance are measured as functions of temperature (77–450 K) on several FeCr₂S₄ and CoCr₂S₄ single crystals (as-grown, annealed in vacuum, annealed in S-atmosphere, and doped) and found to be very sensitive to these treatments. These results are discussed on the basis of the model consisting of donor level due to S-deficiencies in addition to Fe²⁺ and Cr²⁺ levels.     

NH4H2PO4和ND4D2PO4晶体微结构的拉曼光谱研究

本文利用偏振拉曼光谱和第一性原理, 对磷酸二氢铵(NH₄H₂PO₄, ADP)和不同氘含量磷酸二氢铵DADP晶体的晶格振动模式进行了研究. 实验测得了不同几何配置、200–4000 cm^-1范围的偏振拉曼光谱, 分析在不同氘含量条件下921 cm^-1和3000 cm^-1附近拉曼峰的变化. 在ADP晶体中, 基于基本结构单元NH₄⁺ 和H₂PO₄^-基团的振动模, 用第一性原理进行了数值模拟, 进一步明确拉曼峰与晶体中原子振动的对应关系; 通过洛伦兹拟合不同氘含量DADP晶体的拉曼光谱中2000–2600 cm^-1处各峰的变化讨论了DADP 晶体的氘化过程, 结果表明氘化顺序是先NH₄⁺ 基团后H₂PO₄^-基团, 研究结果为今后此类材料的生长和性能优化奠定了基础.     

Oscillation conditions of cw simultaneous dual-wavelength Nd：YAG laser for transitions 4F3／2-4I9／2 and 4F3／2-4I11／2

The operating condition of a cw simultaneous dual-wavelength Nd:YAG laser for both {}^4F_{3/2}-{}^4I_{9/2} (quasi-three-level system) and {}^4F_{3/2}-{}^4I_{11/2}(four-level system) transitions is studied. According to this condition, the cw simultaneous dual-wavelength at 1.06μm and 946 nm in Nd:YAG crystal has been realized experimentally through an adaptive coating design of the cavity mirrors. A total power output of 2.5W of the dual-wavelength at 946nm and 1.06μm has been achieved with an optical conversion efficiency 14.3%. The experimental results are in good agreement with the theoretical analysis.     

Vibrational modes in ZnAl2S4 and CdIn2S4 crystals

Infrared reflectivity spectra and Raman scattering of the ZnAl₂S₄ and CdIn₂S₄ crystals have been investigated. Reflectivity spectra contours were calculated and phonon parameters and dielectric constants were determined. Effective charges for the Zn, Cd, In and S ions of these materials were determined.     

K2NiF4型Sr2CrO4的磁电性质研究

以SrO和CrO₂为原料, 在高温高压的条件下直接反应生成纯相的K₂NiF₄结构的Sr₂CrO₄多晶样品. 结构用粉末X射线衍射及GSAS精修表征. 磁化率测试显示样品存在一个弱的反铁磁相变, 奈尔温度为T_N=95 K. 在奈尔温度以上, 磁化率随温度的变化遵循居里-外斯定律. 对样品进行了电阻测试, 结果显示了样品的绝缘特性.     

Effective ionic charges in CdGa2Se4 and CdGa2S4

Available experimental data (Raman and Infrared) on the optic phonon spectra in defect chalcopyrite crystals CdGa₂Se₄ and CdGa₂S₄ are used to determine the dynamical ionic effective charges. The results are compared with those found in other ternary compounds as spinels and chalcopyrites. An emperical correlation between the normalized Szigeti charges and the optical dielectric constant is discussed.     

Low temperature photoconductivity of ZnIn2Se4 and CdIn2Se4

The photoconductivity of ZnIn₂Se₄ and CdIn₂Se₄ single crystals has been studied at 4.2 K. The spectra are compared to reflectivity spectra and relevant structures are interpreted in terms of interband transitions. The absence of excitonic transitions is discussed in connection with the crystalline perfection.     

Absorption spectra of Ni2+ in (NH4)2Mg(SO4)2·6H2O and Co2+ in Na2Zn(SO4)2·4H2O

Optical absorption spectra of Ni²⁺ in (NH₄)₂Mg(SO₄)₂·6H₂O and Co²⁺ in Na₂Zn(SO₄)₂·4H₂O single crystals have been studied at room and liquid nitrogen temperatures. From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for both the ions in the crystals. The splitting observed for ${}^3\text{T}{}_{\mathrm{1g}}\text{(F)}$ band in Ni²⁺ and ${}^4\text{T}{}_{\mathrm{2g}}\text{(F)}$ band in Co²⁺ at liquid nitrogen temperature have been explained as due to spin-orbit interaction. The extra band observed at 16,325 cm^-1 in the case of Ni²⁺ at low temperature has been interpreted to be the superposition of vibrational mode of SO^2-₄ radical on ${}^3\text{T}{}_{\mathrm{1g}}\text{(F)}$ band. The observed band positions in both the crystals have been fitted with four parameters B, C, Dq and ζ.     

Atomistic computer simulation studies of Sr2RuO4 and Ca2RuO4

Atomistic static computer simulation techniques have been applied to investigate the energetics of defects and dopants in Sr₂RuO₄ (SRO) and Ca₂RuO₄ (CRO). Interatomic potentials have been derived which reproduced the crystal structures of these systems. Solution energies are calculated for different dopant ions to ascertain the site occupied by the dopant ion in the host lattice. Monovalent and divalent ions are predicted to substitute preferentially at the alkaline-earth site in both the systems. Trivalent cations of smaller ionic radii substitute at the Ru sites while those having larger ionic radii prefer to substitute at the Sr or Ca sites in SRO or CRO systems, respectively. In addition, there is a possibility of self-compensation, where a trivalent cation can substitute at both Sr(Ca) and Ru sites. Tetravalent dopants are found to substitute at the ruthenium sites in both systems.     

Li4GeO4-Zn2GeO4赝二元系相图的研究

本文用差热分析和X射线衍射的方法对Li₄GeO₄-Zn₂GeO₄赝二元系相图进行了研究。结果指出,文献中所报道的锂离子导体Li₁₄Zn(GeO₄)₄不是化合物,而是含Zn₂GeO₄的以Li₄GeO₄为基的固溶体,由于Zn₂GeO₄的加入,使Li₄GeO₄的高温相稳定存在于室温。根据研究结果,提出了关于Li₁₄Zn(GeO₄)₄多晶陶瓮样品在室温长期放置后,电导率明显降低的解释。     

Magnetic properties for the Cu2MnSnSe4 and Cu2FeSnSe4 compounds

Magnetic susceptibility χ measurements in the range from 2 to 300 K were carried out on samples of the Cu₂FeSnSe₄ and Cu₂MnSnSe₄ compounds. It was found that Cu₂FeSnSe₄ was antiferromagnetic showing ideal Curie-Weiss behavior with a Néel temperature T_N of about 19 K and Curie-Weiss temperature θ=−200 K, while for Cu₂MnSnSe₄ the behavior was spin-glass with a freezing temperature T_f of about 22 K and Curie-Weiss temperature θ=−25 K. The spin-glass order parameter q(T), determined from the susceptibility data, was found to be in agreement with the prediction of conventional spin-glass theory.     

Raman and infrared spectra of CdIn2S4 and ZnIn2S4

Four one-phonon Raman lines have been found in CdIn₂S₄ (ZnIn₂S₄) spinels at 92 (72) cm^-1, 186 (184) cm^-1, 246 (253) cm^-1, and 367 (372) cm^-1 for incident photon energies well below the energy gap E_G ～ 2.4 (2.2) eV at 300 K. For photon energies close to E_G, the 367 cm^-1 mode underwent a resonant enhancement in CdIn₂S₄ and four infrared active but Raman forbidden F_1u modes appeared in the CdIn₂S₄ and ZnIn₂S₄ Raman spectra: TO modes at 226 (221) cm^-1 and 309 (312) cm^-1, and LO modes at 274 (272) cm^-1 and 340 (342) cm^-1.