Growth,structure and thermal properties of CuAlxGa1‐xSe2 alloys

Ingots of the CuAl_xGa_1‐xSe₂ (0 ≤ x ≤ 1) alloys system were prepared by direct fusion of the stoichiometric mixture of the elements. The analysis of X‐ray Powder Diffraction data showed the presence of one single phase with chalcopyrite tetragonal structure at room temperature for all the studied compositions. The lattice parameters, a and c, and the bond lengths were calculated. The phase transition temperatures were obtained by the onset method from Differential Thermal Analysis measurements performed on samples sealed in evacuated quartz ampoules. Fusion or transition enthalpies were determined from the area of the corresponding DTA peak. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of compounds LixMn1+xFe2–2xO4 with spinel structure in the quasiternary system “LiO0,5 – MnOx – FeOx“

The thermal decomposition of freeze‐dried Li‐Mn(II)‐Fe(III)‐formate precursors was investigated by means of DTA, TG and mass spectroscopy. By the thermal treatment of the prefired precursors between 400 and 1000°C, single phase solid solutions Li_xMn_1+xFe_2–2xO₄ (0 ≤ x ≤ 1) with cubic spinel structure were obtained. To get single phase spinels, special conditions concerning the temperature T and the oxygen partial pressure p(O₂) during the synthesis are required. Because of the high reactivity of the freeze‐dried precursors, in comparison with the conventional solid state reaction, the reaction temperature can be lowered by 200°C. The cation distribution and the properties of the Li‐Mn‐ferrites were studied by chemical analysis, X‐ray powder diffraction and magnetization measurements. It was found that for high substitution rates, almost all lithium occupies the tetrahedral coordinated A‐sites of the spinel lattice AB₂O₄, while at small x‐values, lithium ions are distributed over the tetrahedral and octahedral sites. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Pb on the properties of Sr2YRu1‐xCuxO6 crystals grown from PbO‐PbF2 solutions at high temperatures

Single crystals of Sr₂YRu_1‐xCu_xO₆ with x=0 and x=0.1 were grown using PbO‐PbF₂ based solutions at different temperatures in the range 1150–1350°C. The influence of Pb from the solutions and the Cu from the solid solutions of Sr₂YRu_1‐xCu_xO₆ on the resulting crystals was studied using microstructure and magnetic property measurements. The peaks in the powder X‐ray diffraction patterns and Raman spectra do not change in the case of x=0 crystals but shift in the presence of Cu. A diamagnetic transition indicative of superconductivity was observed in the presence of Cu and an antiferromagnetic behavior with x=0. Based on these results it is concluded that Pb may not be incorporated in the crystals and even if it does the influence is not observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth of the CdGa2(1‐x)Cr2xSe4 compounds by chemical transport method

Single crystals of CdGa_2(1‐x)Cr_2xSe₄ compounds for 0 ≤ x ≤ 1 have been grown by using the chemical vapor transport technique in a closed system. The transporting agent was CdCl₂ in a proportion of 0.75 mg/cc of capsule. The starting material was previously synthetized. The structural characterization on the crystals were done by powder x‐ray diffraction studies. The results show three different phases for various Cr concentration ranges: spinel structure for x ≥ 0.7, rombohedral for 0.6 ≥ x ≥ 0.5 and tetragonal for 0.4 ≥ x ≥ 0. That is, the chromium dilution in the CdCr₂Se₄ compound by Ga atoms produces very significant changes in the structural atomic arrangement. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Composition Dependency of Lattice Anisotropy of TlBX2‐type Chain Mixed Crystals

Variation of the lattice parameters of TlTl_1‐xIn_xSe₂ chain mixed crystals with composition have been studied by X‐ray diffraction technique. The lattice anisotropy ( c/a ) of the TlBX₂‐type mixed crystals changes linearly with substitution of the atoms located both at the center and at the vertices of the BX4 tetrahedra. A brief survey of the important features of the effect of isomorphic atom substitution on the lattice anisotropy of TlBX₂‐type mixed crystals with chain structure has been presented.     

Effect of isomorphic atom substitution on the refractive index and oscillator parameters of TlInS2xSe2(1‐x) (0.25 ≤ x ≤ 1) layered mixed crystals

The optical properties of TlInS_2xSe_2(1‐x)mixed crystals (0.25 ≤ x ≤ 1) have been studied at room temperature through the transmittance and reflectivity measurements in the wavelength range of 400–1100 nm. The spectral dependence of the refractive index for all compositions of studied crystals were obtained. The dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single‐effective‐oscillator model. The compositional dependencies of refractive index dispersion parameters: oscillator energy, dispersion energy and zero‐frequency refractive index were revealed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and investigation of (CuInSe2)x(2ZnSe)1‐x and (CuInTe2)x(2ZnTe)1‐x solid solution crystals

The (CuInSe₂)_x(2ZnSe)_1‐x and (CuInTe₂)_x(2ZnTe)_1‐x solid solution crystals prepared by Bridgman method and chemical vapor transport have been studied. The nature of the crystalline phases, the local structure homogeneity and composition of these materials have been investigated by X‐ray diffraction (XRD) and Electron Probe Microanalysis (EPMA) methods. The analysis revealed the presence of chalcopyrite‐sphalerite phase transition between 0.6 ≤ X ≤ 0.7. Lattice constants, value of σ position parameter and bond length between atoms were also calculated. It was found that the lattice parameters exhibit a linear dependence versus composition. The transmission spectra of solid solution crystals in the region of the main absorption edge were studied. It was established that the optical band gap of these materials changes non‐linearly with the X composition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of MoSe2/Reduced graphene oxide composites with improved tribological properties for oil‐based additives

In this work, we developed a facile and effective hydrothermal method synthesis of MoSe₂ nanoflowers on reduced graphene oxide (RGO) sheets. The as‐prepared MoSe₂/reduced graphene oxide (MoSe₂/RGO) composites are characterized by X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that MoSe₂ nanoflowers were successfully deposited on RGO nanosheets to form a well interconnected hybrid structure. The tribological properties of MoSe₂/RGO composites as lubricating oil additive were investigated by a UMT‐2 ball‐on‐plate friction and wear tester. By the addition of MoSe₂/RGO composites in paraffin oil, the antiwear ability was improved and the friction coefficient was decreased. The based oil with MoSe₂/RGO composites showed better tribological properties than the oil with MoSe₂ and pure oil. The good friction and wear properties of MoSe₂/RGO composites as additives were attributed to the formation of a thin physical tribofilm on the substrate.     

X‐ray powder diffraction structural characterization of Ba1‐xEuxTiO3 ternary oxides

The single‐phase Ba_1‐xEu_xTiO₃ (0.1≤x≤0.4) samples have been synthesized by solid state reaction under high pressure and ‐temperature. X‐ray powder diffraction data was determined by MS Modeling using Reflex Powder Indexing technique. The Ba_1‐xEu_xTiO₃ series exhibited an interesting orthorhombic‐tetragonal‐cubic structural transformation as Eu composition increases, the distinct change of the X‐ray diffraction peak profile in the vicinity of 45.5º is characteristic of structural transformation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and magnetic‐optical properties of Sr3Gd(BO3)3 and Sr3TbxGd1‐x(BO3)3 single crystals

Single crystals of Sr₃Gd(BO₃)₃ (SGB) and Sr₃Tb_xGd_1‐x(BO₃)₃ (TSGB) with dimension Ø 20 mm×20 mm have been grown by Czochralski method. The grown crystals were characterized by X‐ray powder diffraction analysis which showed the crystals belong to hexagonal structure with lattice parameters of a=b=1.254 nm, c=0.926 nm (SGB) and a=b=1.253 nm, c=0.925 nm (TSGB). In TSGB, x=17.7% was obtained by X‐ray fluorometry which showed the segregation coefficient of Tb is closed to 1. The transmission spectrum was measured, which indicated the crystals have high transmittance in 400‐1100 nm region. The Faraday rotation of single crystals at 532 nm wavelength was measured at room temperature. Finally, the Verdet constants were investigated, (SGB) V=17.9 degcm^‐1T^‐1 and (TSGB) V=21.3 degcm^‐1T^‐1. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and magnetic properties of Nd‐doped ZnO nanoparticles

Nd‐doped ZnO nanoparticles with different concentration were synthesized by sol‐gel method. The structures, magnetic and optical properties of as‐synthesized nanorods were investigated. X‐ray diffraction (XRD) and x‐ray photoelectron spectroscopy (XPS) results demonstrated that Nd ions were incorporated into ZnO lattice; but Zn_1‐xNd_xO nanoparticles with Nd concentration of x = 0.05 showed Nd₂O₃ phase, so the saturation concentration of Nd in Zn_1‐xNd_xO is less than 5 at%. Vibrating sample magnetometer (VSM) measurements indicated that Nd doped ZnO possessed dilute ferromagnetis behaviour at room temperature. Photoluminescence spectroscopy (PL) showed that Nd ions doping induced a red slight shift and decrease in UV emission with increase of Nd concentration.     

Properties of AgGa1‐xInxSe2 single crystals grown by Bridgman method

High‐pure and single‐phase AgGa_1‐xIn_xSe₂ (x=0.2) polycrystalline was synthesized by the mechanical and temperature oscillation method. Adopting the modified Bridgman method an integral AgGa_1‐xIn_xSe₂ single crystal with diameter of 14 mm and length of 35 mm has been obtained at the rate of 6 mm/day. It was found that there is a new cleavage face which was (101), and observed the four order X‐ray spectrum of the {101} faces. By the method of DSC analysis the melting and freezing points of the AgGa_1‐xIn_xSe₂ (x=0.2) single crystal were about 828°C and 790°C. The transmission spectra of the AgGa_1‐xIn_xSe₂ (x=0.2) sample of 5×6×2 mm³ were obtained by means of UV and IR spectrophotometer. The limiting frequency was 774.316nm and the band gap was 1.6eV. It can be found in the infrared spectrum that the infrared transmission was above 60% from 4000cm^‐1 to 600cm^‐1. The value of α in 5.3µm and 10.6µm were 0.022cm^‐1 and 0.1cm^‐1 respectively. All results showed that the crystal was of good quality. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and thermal studies on pure ADP,KDP and mixed K1‐x(NH4)xH2PO4 crystals

The investigations on the formation of mixed crystals of ammonium dihydrogen orthophosphate (ADP) and potassium dihydrogen orthophosphate (KDP) i.e. potassium ammonium dihydrogen phosphate, K_1‐x(NH₄)_xH₂PO₄ have been presented in this paper. Pure and mixed crystals of ADP and KDP have been grown by slow evaporation technique from the supersaturated solution at an ambient temperature 26±1 °C for ammonium concentration x in the range 0.0 ≤ x ≤ 1.0 in the case of mixed crystals. Crystal compositions were determined by flame atomic absorption spectroscopy and chemical analysis. The results of the X‐ray analysis of the grown crystals are also reported. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the kinetic process of dehydration and the high temperature phase behaviour. DTA showed the distinct thermal events attributed to dehydration of ADP, KDP and K_1‐x(NH₄)_xH₂PO₄. The results of thermal analysis and chemical analysis are consistent with each other. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure refinement of CuxAg1‐xInTe2 bulk material determined from X‐ray powder diffraction data using the Rietveld method

The influence of the Cu‐content in the quaternary compounds Cu_xAg_1‐xInTe₂ (0 ≤ x ≤1) on the structural properties of the bulk material was discussed. Bulk ingot materials of Cu_xAg_1‐xInTe₂ solid solutions (x = 0.0, 0.25, 0.50, 0.75 and 1.0) have been synthesized by fusion of the constituent elements in the stoichiometric ratios in vacuum‐sealed silica tubes. The materials compositions were confirmed by using energy dispersive analysis of X‐rays (EDAX). X‐ray powder diffraction measurements were performed for all the prepared samples at 300 K in step scanning mode. The analysis of X‐ray data has indicated that the crystal structure of the prepared materials with different compositions is single‐phase polycrystalline materials corresponding to the tetragonal chalcopyrite structure with space group I 2d. The crystal structural parameters were refined by Rietveld method using the Full Prof program. The refined lattice constants (a and c), anion positional parameter, u, and the determined bond distances and angles were found to vary with composition, x, attaining zero tetragonal distortion at x ≈ 0.75, which corresponds to an ideal tetragonal unit cell. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of 4‐Aminopyridinium‐4‐nitro phenolate single crystals

Organic optical material 4‐Aminopyridinium‐4‐nitro phenolate (4AP4NP) has been synthesized, and single crystals of size 20 x 14 x 6 mm³ have been grown from acetone solvent at room temperature by solvent evaporation technique. The grown crystals have been characterized by X‐ray diffraction to determine the cell parameters, and by FT‐IR technique to confirm the formation of the expected compound. The crystal belongs to monoclinic crystal system with space group P2₁/a.The structural perfection of the grown crystals has been analyzed by high‐resolution X‐ray diffraction (HRXRD) rocking curve measurements. The thermal stability of the compound has been determined by TG‐DTA curves. The transmittance of 4AP4NP has been used to determine the refractive index n; the extinction coefficient K and both the real ε_r and imaginary ε_i components of the dielectric constant as functions of photon energy. The optical band gap of 4AP4NP is 2.4 eV. The dielectric and mechanical behavior of the specimen was also studied. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Czochralski growth of Lu1‐xScxBO3:Ce solid solution crystals

Single crystals of Lu_1‐xSc_xBO₃:Ce (x=0.2, 0.3, 0.5, 0.7) were grown by Czochralski method. Continuous solid solution with calcite structure and a linear compositional dependency of crystal lattice parameter in the system Lu_1‐xSc_xBO₃:Ce are formed and their symmetry belong to hexagonal system with R3c space group checked by X‐ray powder diffraction. The electron probe micro‐analysis measurements show that the main inclusions in Lu_1‐xSc_xBO₃:Ce crystals are in the form of Sc rich oxide and Ce rich oxide. The ICP‐AES tests show that the more Sc ion content in Lu_1‐xSc_xBO₃:Ce, the smaller effective segregation coefficient of Ce in crystal will be. The X‐ray excited luminescence spectra of Lu_1‐xSc_xBO₃:Ce crystals all present a double peaked emission band with maxima round 370 and 400 nm corresponding to Ce³⁺ emission and a self trapped excitons (STE) band peaking at 269 nm. In addition, due to high density, high relative light yield, fast decay time and no‐hygroscopic property, Lu_0.8Sc_0.2BO₃:1 at%Ce crystal could be a good candidate material for scintillation application by improving the crystal quality and cerium concentration. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and characterization of the CdGaCrSe(4‐X)S(X) system

Single‐crystal of the CdGaCrSe_(4‐X)S_(X) system (x = 0; 1; 2; 3; 4) were grown by the chemical vapour‐phase transport technique. The crystals were obtaine by using CdCl₂ as transporting agent for the composition with x = 1, and CrCl₃ for those with x = 0; 2; 3 and 4. X‐ray powder diffraction analysis indicated that some of the samples crystallizes in the tetragonal system with space group I‐4 (CdGaCrSe₃S , x = 1; CdGaCrSe₂S₂ , x = 2), or in a cubic system with space group Fd‐3m (CdGaCrSeS₃, x = 3; CdGaCrS₄, x = 4), however the sample of CdGaCrSe₄ (x = 0) crystallizes in rhombohedral system. Magnetic measurements show significant changes in the magnetic interactions behaviour probably due to the anionic substitutions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of big single crystals of a new magnetic superconducting double perovskite Ba2PrRu1–xCuxO6

Single crystals of Ba₂PrRu_1–xCu_xO₆ with x = 0 to 0.2, have been grown from high temperature solutions of a mixture of PbO‐PbF₂ in the temperature range 1100–1200 °C. Thin crystals with mostly a hexagonal and triangular plate like habit measuring up to 1–2 mm across and 0.1–0.2 mm thick were obtained. The size, quality and morphology of the crystals were improved by varying the solution volume as well as additives like B₂O₃. Large crystals measuring up to 3 mm across and 0.3 to 0.5 mm thick were obtained with 5–7 wt% solute concentration and 0.51 wt% of B₂O₃. The ZFC curves exhibit a spin glass like behavior with x = 0 and a superconducting transition at 8 to 11 K depending on x = 0.05 to 0.1. The transition was also influenced by the growth temperature and post growth annealing. Powder x‐ray diffraction, EDS and Raman spectroscopic measurements confirm the presence of Cu in the crystals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of hexagonal ferrites BaFe12‐2xZnxTixO19 (0 ≤ x ≤ 2) by thermal decomposition of freeze‐dried precursors

Substituted barium hexaferrites, BaFe_12‐2xZn_xTi_xO₁₉ (0 ≤ x ≤ 2), have been synthesized by thermal decomposition of freeze‐dried acetate precursors. Decomposition and phase formation were investigated by means of thermal analysis, XRD and IR spectroscopy. The initially amorphous decomposed precursor reacts to the substituted hexaferrite via a spinel‐like maghemite (γ‐Fe₂O₃) and Zn/Ti containing spinel ferrites. The synthesis method allows a decrease of the reaction temperature and time, necessary for producing a single phase hexaferrite. At relative low reaction temperatures, the substitution rate x shows remarkable differences at different iron sublattices. For x ≤ 0,8 this selective substitution results in an increase of magnetization as x grows. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermoelectrical properties of In1‐xGaxAs and InAs crystals irradiated with fast electrons

The thermoelectric power in In_1‐xGa_xAs (x = 0,01;0,04) solid solutions and InAs crystals irradiated with fast electrons by the energy of 6 MeV and dose of 10¹⁶‐ 2 x 10¹⁷ el/cm^‐2 on the interval 80‐400 K have been investigated. It is revealed that in the all crystals the value of the thermoelectric power is decreased under irradiation that resulted from the growth of the free electron concentration to form radiation induced defects of the donor type. It has been determined that in the initial InAs after irradiation, the charge carriers scatter on optical phonons and in In_1‐xGa_xAs solid solutions they do on optical phonons and ionized impurities. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)