Properties of AgGa x In1 – x Se2 Solid Solutions

AgInSe₂, AgGaSe₂, and AgGa _x In_{1 – x} Se₂ crystals consisting of large blocks were grown by the horizontal Bridgman process, and their composition and lattice parameters were determined by electron probe x-ray microanalysis and x-ray diffraction. The lattice parameters of the solid solutions were shown to vary linearly with x. Differential thermal analysis was used to determine the phase-transition temperatures of the crystals and to map out the AgInSe₂–AgGaSe₂ phase diagram, which was also evaluated thermodynamically. The density of the AgGa _x In_{1 – x} Se₂ solid solutions was found to vary linearly with composition, while their microhardness shows a maximum.     

Pressure Effects on the Structural and Elastic Properties of AgGaS2–AgGaSe2Crystals: An X-ray Diffraction Study

The structural and elastic properties of AgGa(S_{1 – x} Se _x )₂crystals with the tetragonal chalcopyrite structure were studied by x-ray powder diffraction at pressures of up to 4 GPa. All of the crystals were found to have anisotropic elastic properties, with thec-axis compressibility notably exceeding the a-axis compressibility. The compression along the longer bond Ag–S(Se) is smaller than that along the Ga–S(Se). The compressibility anisotropy in the solid solutions and AgGaSe₂is stronger than that in AgGaS₂. The composition dependences of the elastic constants are nonlinear.     

Preparation and dta of some AIBIIICVI2 compounds

Single crystals of AgGaSe₂, AgGaTe₂, AgInSe₂ and AgInTe₂ were grown by a step-wise slow cooling technique. Phase transformations on the two Tellurides have been detected by DTA on powder samples.     

Ag2SeGa2Se3 pseudobinary phase diagram

The pseudobinary Ag₂Se-Ga₂Se₃ phase diagram has been redetermined by differential thermal analysis, x-ray diffraction, and crystal growth studies. A new ternary phase, Ag₉GaSe₆, has been observed, and the phase boundaries of the solid solutions based on AgGaSe₂ and Ga₂Se₃ have been measured. The optical scattering observed in slow-cooled crystals of AgGaSe₂ is due to precipitates of a Ga₂Se₃-based solid solution, which has the approximate composition AgGa₇Se₁₁. The new Ag₂Se-Ga₂Se₃ diagram differs significantly from the one given by Palatnik and Belova but is qualitatively similar to the Ag₂S-Ga₂S₃ diagram recently reported by Brandt and Krämer.     

Optical properties of AgGaSe2 thin films

AgGaSe₂ films were grown using the flash evaporation technique on glass substrates at various substrate temperatures. The optical absorption of these films in the energy range 1.4–1.9 eV was studied and the films were found to possess direct band gap material. The photoconductivity of the AgGaSe₂ films was studied as a function of (i) light intensity, (ii) temperature and (iii) response times. The photoconductivity response spectra of the AgGaSe₂ films were utilized to determine the band gap energies as a function of the substrate temperature. The implications are discussed.     

Off-stoichiometric Melt Growth of LuBa2Cu3O6 + x Crystals

Superconducting LuBa₂Cu₃O_{6 + x} crystals up to 5 × 5 × 0.2 mm in dimensions were grown by spontaneous crystallization during slow cooling of Lu₂O₃–BaO–CuO melts and were characterized by thermal analysis, x-ray diffraction, and electron probe x-ray microanalysis.     

Preparation and formation mechanism of silver gallium selenide powders prepared via the sol–gel method

The sol–gel method followed by selenization was developed to synthesize AgGaSe₂ powders in this study. The molar ratio of gallium ions to silver ions was controlled to prepare pure AgGaSe₂ powders. Two selenization processes were employed to investigate the formed phases of the obtained powders. When the sol–gel-derived precursors were mixed with selenium powders, pure-phase AgGaSe₂ powders were formed after selenization. Without mixing selenium powders, AgGaSe₂ was produced with the impurity phase of Ag₉GaSe₆. A three-step reaction mechanism for the formation of AgGaSe₂ is proposed. Ag₂Se is initially formed in the first step, and then reacts with constituent species as well as hydrogen to produce Ag₉GaSe₆. Finally AgGaSe₂ is formed from the reaction among Ag₉GaSe₆, Ga₂O₃, Se and H₂. When the selenium powders are mixed with the precursors, liquid selenium is formed in the selenization process and effectively promotes the reactions.     

Single-crystal growth of La2−2x Sr1+2x Mn2O7 under pressure

Large single crystals of La_2–2x Sr_1+2x Mn₂O₇ (x=0.3 to 0.525) have been prepared under controlled atmospheric conditions. The crystals were grown by the floating-zone technique in an image furnace under a mixed oxygen/argon atmosphere pressurized to 6–8×10⁵ Pa. Rectangular single crystals with sizes up to 50×9×4 mm³ have been obtained. The phase-purity, composition, and quality of the crystals were analyzed by X-ray diffraction and electron probe microanalysis. The magnetic behavior is found to be sensitive to the composition of the atmosphere during growth.     

Nanoporous Crystalline Material CsLiB6O10

CsLiB₆O₁₀ crystals up to 60 × 40 × 20 mm in dimensions were prepared by top-seeded solution growth, and their interaction with water was studied. The crystals were found to be subject to hydration followed by hydrolysis, during which water leaches Cs from the structural channels to yield Cs₂B₁₀O₁₆ · 8H₂O as the final product. The channel dimensions are not large enough to incorporate ethanol or acetone molecules.     

CпEктп ЭЛEКтPOЛюмИнECЦEнЦИИ мOнoКпнCтAЛЛ AgGaS2

The paper deals with the mechanism of electroluminescent emission observed for the first time in AgGaS₂ single crystals. The recombination radiation is due to the transitions from the level located at 0.368 eV below the conduction band T₆ to the corresponding valence bands (peaks P₁ and P₄) and to the transitions of electrons from the conduction band to the local levels at 0.446 eV and 0.486 eV from the top of the valence band T₇ (peaks P₂ and P₃) respectively.     

Effect of Copper Doping on the Optical Properties of AgxGaxGe1 ? xSe2 (0.12 ≤ x ≤ 0.25) Single Crystals

Single crystals of AgGaSe₂-GeSe₂ γ-solid solutions are investigated. The Ag_xGa_xGe_{1 − x} Se₂ (0.12 ≤ x ≤ 0.25) solid solutions are anisotropic p-type semiconductors with a 290-K band gap of about 0.26 eV. The high defect density in the crystals results in static disordering and the formation of density-of-states tails in the band gap, reducing their transmittance. Cu doping leads to bleaching in the optical window of the crystals (visible through near-IR spectral region). A model is proposed for the interaction between the dopant atoms and structural defects in the crystals. The radiation hardness and laser damage threshold of Ag_xGa_xGe_{1 − x} Se₂ are evaluated. __________ Translated from Neorganicheskie Materialy, Vol. 41, No. 9, 2005, pp. 1054–1057. Original Russian Text Copyright ? 2005 by Davidyuk, Olekseyuk, Shavarova, Gorgut.     

X-ray dosimetric characteristics of AgGaS<Subscript>2</Subscript> single crystals grown by chemical vapor transport

Using chemical vapor transport, we have grown AgGaS₂ single crystals possessing large room-temperature X-ray induced conductivity and X-ray sensitivity coefficients, which allows the single crystals to be recommended for use as key elements of various uncooled and very fast X-ray detecting devices and systems.     

Crystal growth of Bi2Sr2CuO6 from flux system KCl-KF and its superconductivity

Single crystals of Bi₂Sr₂CuO₆ (BSCO) were grown from high-temperature solution using KCl-KF as flux. Differential thermal analysis (DTA) of the starting materials enabled an appropriate temperature programme to be introduced for crystal growth by spontaneous nucleation. By means of the improved thermogravimetric (TG) method, Bi₂Sr₂CuO₆ crystals were grown after determination of the crystallization temperature. A single crystal in the form of a thin rectangular platelet up to 6×4 mm² was obtained and was identified by X-ray powder pattern and by scanning electron microscopy (SEM). Analyses were performed by using high-resolution electron probe microanalysis (EPMA), which indicated that it is the nonstoichiometric compound Bi_2+xSr_2–xCuO₆. The superconducting properties are strongly dependent on the composition of Bi and Sr in the crystals and on heat treatment. The transition temperature of 7 K with 0.5 K width for as-grown crystals, has been obtained.     

Growth and characterization of some I–III–VI2 compound semiconductors

Single crystals of CulnS₂, CulnSe₂, CulnTe₂, CuGaS₂, AgGaS₂ CulnSSe, AgGaSSe have been grown by chemical vapour transport technique on the basis of a new general thermodynamical model which enables the minimum source temperature T _s, and the minimum deposition temperature, T _d, to be determined. X-ray analysis, X-ray photoelectron spectroscopic analysis, surface analysis, and microhardness studies have been carried out on the single crystals grown.     

Growth of NiWO4 crystals from a Na2W2O7 flux

Well-formed rod crystals of NiWO₄ were grown from a Na₂W₂O₇ flux by a slow cooling method. The solubility of NiWO₄ in Na₂W₂O₇ increased with increasing temperature. At 1100 °C, NiWO₄ was dissolved in Na₂W₂O₇ at a concentration of about 45 mol %. The eutectic temperature was 615± 5 °C. Flux growth was conducted by heating mixtures at 1100 °C for 10 h, followed by cooling to 500 °C at a rate of 5 °C h^–1. The brownish and transparent crystals up to 15 mm in length were grown from the mixtures of about 40 g. The most suitable solute content was 30 mol %. The grown crystals were bounded by the {100}, {010}, {110}, {102}, and {111} faces. In certain instances, the {111} faces disappeared. The EPMA data showed that sodium from the flux used was not contained within the grown crystals. The crystals of NiWO₄ had a d.c. electrical resistivity of about 1 × 10¹¹ cm.     

Basic study of single crystal fibers of Pr:Lu3Al5O12 scintillator for gamma-ray imaging applications

Single-crystalline fibers were grown from 0.25, 0.70, and 1.50 mol% Pr-doped Lu₃Al₅O₁₂ (LuAG) melts by the micro-pulling down (μ-PD) method with a diameter of 0.3-0.5 mm and a length of about 200 mm. They were cut to 10 mm long specimens, and their scintillation properties, including light yield and decay time profile, were examined. These results were compared with corresponding properties of the specimens (0.8×0.8×10 mm³) cut from the bulk crystals produced by conventional Czochralski (CZ) growth. The μ-PD-grown fibers demonstrated relatively low light yield and had the same decay time constant when compared with those of the samples cut from the CZ-grown crystals. The fiber crystals were used to assemble scintillating arrays with dimensions of Ø 0.5×10 mm²×20 pixels and Ø 0.3×10 mm²×30 pixels coated by a BaSO₄ reflector. After optical coupling with a position sensitive photomultiplier tube, the fiber-based arrays demonstrated acceptable imaging capability with a spatial resolution of about 0.5 mm.     

The investigation of structural, electrical, and optical properties of thermal evaporated AgGaS2 thin films

AgGaS₂ (AGS) thin films were deposited onto glass substrates by sequential thermal evaporation of AgGaS₂ single crystalline powder and excess silver (Ag) interlayer. Systematic optimization to obtain single phase AgGaS₂ thin films was carried out by changing the thickness of the excess silver layer. The structure and composition of as-grown and annealed films were studied by means of X-ray diffraction and energy dispersive X-ray analysis, respectively. The optical properties of AGS thin films determined by transmittance and reflection measurements showed that they had quite high absorption coefficient with the values around 10⁴ (cm⁻¹). The calculated band gap values were found to be between 2.30 and 2.75 eV depending on annealing temperature. The refractive index (n) and extinction coefficient (k) of the films were determined by the envelope method. Finally, photo-electrical measurements under different illumination intensities were carried out, and different sensitizing and recombination centers were defined.     

Growth of ZnSiP2 from tin solution and temperature composition diagram of the ZnSiP2: Sn system

ZnSiP₂ crystals (1 cm or more in length) have been grown from tin solution on a reproducible basis. The dimensions of the largest crystals obtained were 1.7×0.25×0.03 cm³ and 2×0.1×0.02 cm³. The temperature of the reaction region was 1050 to 1080° C and the cooling rate used to form these crystals was 7.5°C h^–1.A practical temperature-composition section of the ZnSiP₂:Sn phase diagram has been determined by differential thermal analysis, X-ray diffraction measurements and microscopic studies. The resulting information on the liquidus temperature variation with composition served to give better control of ZnSiP₂ growth from tin solution. It was concluded that ZnSiP₂ reacted eutectically with Sn and the eutectic composition was close to 100%.     

Melt growth and characterization of Mg2Si bulk crystals

We have grown Mg₂Si bulk crystals by the vertical Bridgman method using a high-purity Mg (6N-up) source. The grown crystals were single-phase Mg₂Si and had well-developed grains (1-5 mm³). Laue observations and SEM-EDX observations confirmed that crystalline quality in the grains was single crystal with stoichiometric composition. Electron concentration of the single crystalline specimens grown from 6N-up-Mg was 4.0 × 10¹⁵ cm^− 3 at room temperature (RT). This value is more than one order of magnitude lower than that of specimens grown from 4N-Mg [(5-7) × 10¹⁶ cm^− 3]. The Hall mobility of 14,500 cm²/Vs was observed at 45 K in the crystals grown from 6N-up-Mg. We also found that Al impurity plays an important role in the crystals grown from a low-purity Mg source. From the optical absorption measurement, we estimated that the indirect energy gap was about 0.66 eV at 300 K and about 0.74 eV at 4 K.     

Characteristics of pulse electrodeposited AgGaSe2 films

In this work, the pulse electrodeposition technique has been employed for the first time to deposit AgGaSe₂ films. The films were deposited at room temperature from a bath containing Analar grade 10 mM silver nitrate, 10 mM gallium nitrate and 10 mM SeO₂. The deposition potential was maintained as—0.68 V (SCE). Tin oxide coated glass substrates (5.0 ohms/sq) was used as the substrate. The duty cycle was varied in the range of 6–50 %. The XRD profile of the thin films deposited at different duty cycles indicate the peaks corresponding to AgGaSe₂. Atomic force microscopy studies indicated that the surface roughness increased from 0.95 to 1.25 nm with duty cycle. The transmission spectra exhibited interference fringes. Refractive index of 2.71 was observed in the wavelength range 600–1,000 nm. Electrochemical Impedance studies indicated a single semicircle. The grain boundary resistance decreased with increase of duty cycle.