Crystal Growth and Differential Thermal Analysis of AgGaSe2

High quality AgGaSe₂ single crystals with 20 mm in diameter and 55 mm in length have been grown by Bridgman technique. It is found that there is a second phase of Ag-rich Ga₂Se₃ (or named AgGa₇Se₁₁) in the AgGaSe₂ crystal. It is concluded by discussions with the DTA results and the phase diagram that single crystals grown from polycrystalline materials with stoichiometric composition must contain a second phase of Ag-rich Ga₂Se₃. This result is helpful for the heat treatment, in which what and how much is added and what temperature is chosen for the heat treatment, are very important.     

Electrical properties of AgGaSe2 epitaxial layers

Epitaxial layers of AgGaSe₂ with thicknesses in the range from 50 to 70 nm were deposited onto (111)A-oriented semi-insulating GaAs substrates by flash-evaporation in the substrate temperature range T_S = 825 … 900 K. Films grown at T_S ≦ 850 K are n-type conducting whereas p-type conductivity was observed at T_S ≧ 875 K. In the p-type samples two acceptor states with ionization energies of 60 and 410 meV were found from an analysis of the electrical measurements.     

High-temperature heat capacity,thermodynamic properties and debye temperature of CuGe2P3

The heat capacity at constant pressure of CuGe₂P₃ is measured in the temperature range from 180 to 550 K. Standard enthalpies and entropies relative to 298.15 K are calculated from the heat capacity data. The Debye temperature in the high-temperature limit is estimated to be about 710 K.     

AgGaSe2 晶体的改进Bridgman法生长

本文报导了一种AgGaSe2生长工艺,可有效地从熔体中排出非凝聚气相杂质,结合一项改进的坩埚镀碳技术,提高了生长优质AgGaSe2单晶的成品率.文中还给出了晶体样品的红外观测,红外透过光谱和光电流谱,以及可调谐TEA CO2激光倍频的实验结果.     

Interatomic interaction aspect of phase transition in AgInS2 crystals

The structural parameters of two modifications of AgInS₂ are determined. The geometrical model of phase transition is discussed. Crystallochemical comparison reveals the absence in the two modifications of significant differences in atomic interactions. The changes in atomic interaction with the temperature increase and the role of dynamical changes in phase transition are discussed.     

Studies of the Growth Habits of the AgGaSe2 Single Crystal

High quality AgGaSe₂ single crystals with 20 mm in diameter and 55 mm in length have been grown by the modified Bridgman technique and the growth habits of AgGaSe₂ single crystals have been investigated in detail. It is found that the shape of the growth ampoule affects greatly the nucleation and the growth of AgGaSe₂ single crystal. A new cleavage face (101) and the natural faces are observed in the as-grown crystals. For some cases, the growing direction is normal to the (316) face.     

Synthesis by organic molten salt method and characterization of chalcopyrite AgInS2 nanorods

In this paper, chalcopyrite AgInS₂ nanorods were synthesized for the first time by a one‐step, ambient pressure, environment friendly organic molten salt (OMS) method at 200 °C. The as‐synthesized products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. The XRD results reveal that the as‐synthesized products at 120–160 °C under ambient pressure contain AgIn₅S₈ which will decrease with the increase of growth temperature. A sample containing only the chalcopyrite AgInS₂ phase is successfully obtained at 200 °C. Furthermore, the elemental compositions are found to become increasingly stoichiometric with increasing temperature. UV‐Vis and photoluminescence (PL) spectra are utilized to investigate the optical properties of AgInS₂ nanorods. By testing on UV‐Vis spectra, it is concluded that the limiting wavelength of the AgInS₂ nanorods is 661 nm and the band gap is 1.88 eV. A broad red emission band peak centered at about 1.874 eV (662 nm) is clearly observed at room temperature, and the intensity of the emission increases with excitation wavelength. In addition, the photoluminescence quantum yield (PLQY) of the nanocrystals at the excitation wavelength of 250 nm was determined to be 13.2%. A possible growth mechanism of AgInS₂ nanorods was discussed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

坩埚旋转下降法生长硒镓银单晶体

本文报道了硒镓银多晶原料合成与单晶生长的新方法--熔体温度振荡法和坩埚旋转下降法.5～6N高纯Ag、Ga、Se单质按AgGaSe2化学配比富0.5;Se配料,1100℃下合成并在熔点附近进行温度振荡,获得了高纯单相致密的AgGaSe2多晶材料.用合成的多晶为原料,采用坩埚旋转下降法生长出φ22×80mm的AgGaSe2单晶锭.晶体外观完整,在10.6μm附近红外透过率达62.4;,吸收系数低于0.01cm-1,对10.6μm CO2激光实现倍频,能量转换效率达12;.     

RHEED Measurements of AgGaSe2 thin films flash evaporated onto {111} a-GaAs

AgGaSe₂ thin films were prepared by flash evaporation on {111} A-oriented GaAs substrates and investigated by reflection high energy electron diffraction (RHEED). Epitaxial growth takes place in the substrate temperature interval of T_s = 845–920 K. The azimuthal orientation of the deposit on the substrate is discussed, supposing a AgGaSe₂ c/a ratio of 1.82. It is shown that detection of twin formation in the films is possible from RHEED measurements in the <211>-azimuths with respect to the substrate.     

Thermal conductivity and specific heat of tellerium-based chalcogenide glasses

The specific heat and thermal conductivity of tellerium-based chalcogenide glasses are reported, together with their glass transition and synthesizing temperatures. The thermal conductivity has been measured in the temperature range between 100 and 500 K while the specific heat was determined at temperatures between 373 and 600 K. Below the glass transition temperature, both physical parameters were observed to be temperature independent.     

Low temperature thermal conductivity and specific heat of elastomers

The specific heat C and thermal conductivity κ of polybutadiene are characteristic of all non-crystalline materials at temperatures below ≈ K, reflecting the presence of localized excitations. The changes in C and κ with variation in crosslinking suggest that the relaxation times of the localized excitations may vary with crosslink density. Extension of an elastomer does not reveal a change in density of localized excitations as monitored by measuring κ, possibly because other phonon scattering mechanisms mask the effect. For T ? 10 K the phonon mean-free-path is independent of the microscopic anisotropy of the elastomer.     

Low temperature specific heat of doped and undoped glasses

In this work we have measured the specific heat, c_p, of several glasses between 2 and 160 K. The experiments were performed in low silica calcium aluminosilicate (prepared under vacuum and room atmosphere conditions), in silicate and in fluoride glasses. The influence of neodymium, iron and cobalt in c_p values at low temperature was also investigated. The scaling proposed by Liu and Löhneysen was used to analyze the experimental data. The temperatures in which the maxima in c_p/T³, the so called boson peak, occur are discussed in terms of the Hrubý coefficient, which provides information about the glass forming ability.     

Compressibility in the Tetragonal Phase of AgInS2 From the X-ray Diffraction Data under High Pressure

The lattice parameters a and c as well as the compressibilities for different directions in the AgInS₂ chalopyrite-type compound are determined as a function of pressure up to 5 GPa using a powder X-ray technique under high pressure. It is found that the compressibility is anisotropic, with compressibility along the tetragonal c-axis (𝓏_c) being smaller than that along the a-axis (𝓏_a). It is shown that as pressure rises the axial ratio c/a increases and as a result the tetragonal distortion δ = 2 - c/a reduces.     

Compressibility in the Orthorhombic Phase of AgInS2 from the X-ray diffraction data under high pressure

The compressibilities for different crystallographic directions in the orthorhombic modification of the ternary AgInS₂ compound were studied as a function of pressure up to 4.5 GPa by the X-ray poweder diffraction method under high pressure. The anisotropy of compressibility was found to exist and between the principal components of compressibility tensor the relation χ_c > χ_a > χ_b was observed. For the orthorhombic modification the bulk modulus is smaller than that for tetragonal one.     

AgGaSe2 on {100} and {110} GaAs—Special Features of Epitaxial Growth

AgGaSe₂ thin epitaxial layers onto {100} and {110} oriented GaAs substrates were prepared by flash evaporation technique and investigated by the RHEED method (reflection high energy electron diffraction). Special epitaxial relationships were found and the results will be discussed.