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)     

Infrared optical properties of (CuGe2P3)1−x(6 Ge)x solid solutions

Infrared reflectivity spectra of (CuGe₂P₃)_1−x(6 Ge)_x mixed crystals with compositions in the range x = 0.07–0.33 are measured at room temperature in the wavenumber range from 180 to 4000 cm⁻¹. An analysis of the spectra reveals six vibrational modes. The composition dependence of the mode frequencies and of the free carrier concentration and mobility is given and compared with infrared optical data for CuGe₂P₃.     

Magnetic properties of the CrSxTe1−x (x = 0−0.2) solid solutions

On the basis of X-ray, magnetic and neutron diffraction measurements the range of solubility in the CrS_xTe_1−x (x = 0−0.2) system has been established and the magnetic phase diagram of the system has been plotted. The decrease of magnetization at low temperature and the additional reflections in the neutron diffraction patterns are associated with the formation of noncollinear magnetic structure which is characterized by the antiferromagnetic component of the magnetic moments. This component has the orthorhombic unit cell with \documentclass{article}\pagestyle{empty}\begin{document}$ a_M = \sqrt {3a_0 } $\end{document}, b_M = a₀, c_M = c₀. The character of the exchange interactions giving rise to this magnetic structure is discussed.     

Effect of temperature and isomorphic atom substitution on optical absorption edge of TlInS2xSe2(1‐x) mixed crystals (0.25 ≤ x ≤ 1)

The optical properties of the TlInS_2xSe_2(1‐x)mixed crystals (0.25 ≤ x ≤ 1) have been investigated through the transmission and reflection measurements in the wavelength range of 400–1100 nm. The optical indirect band gap energies were determined by means of the analysis of the absorption data. It was found that the energy band gaps decrease with the increase of selenium atoms content in the TlInS_2xSe_2(1‐x)mixed crystals. The transmission measurements carried out in the temperature range of 10–300 K revealed that the rates of change of the indirect band gaps with temperature are γ = –9.2×10^–4 eV/K, –6.1×10^–4 eV/K, –4.7×10^–4 eV/K and –5.6×10^–4 eV/K for TlInS₂, TlInS_1.5Se_0.5, TlInSSe and TlInS_0.5Se_1.5 crystals, respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

Photoelectric and photothermal investigations of Zn1‐x‐yBexMnySe solid solutions

Zn_1‐x‐yBe_xMn_ySe solid solutions were grown from the melt by the high pressure Bridgman method. Optical, luminescence, photoelectric and photothermal properties of this material were investigated. Interpretation of the piezoelectrically detected photoacoustic spectra was performed using Jackson and Amer theory. From the spectral dependence of the amplitude and phase of photoacoustic signal as well as from photoluminescence spectra the variation of energy gap with composition was determined. The values of thermal diffusivity were derived from the dependence of photoacoustic signal on modulation frequency of the laser radiation illuminating the sample. The photoluminescence‐excitation spectra and photoconductivity spectra were measured. The origin of luminescence in Zn_1‐x‐yBe_xMn_ySe was discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal expansion in the AgGa(S1−xSex)2 solid solutions from X-ray diffraction data

The lattice parameters a and c as well as the axial thermal expansion coefficients in the AgGa(S_1-xSe_x)₂ solid solutions with chalcopyrite-type structure were determined as a function of temperature in the range from 80 to 700 K and composition x using an X-ray powder diffractometry technique. It is found that the thermal expansion coefficients were anisotropic and for all the solid solutions the thermal expansion coefficients along the tetragonal c-axis were negative whereas those along the a-axis and the volume coefficients were positive. The directions in which the crystal thickness does not change as temperature varies, were found. The composition dependences of these coefficients were non-linear.     

Thermal induced structural properties of silver(I) sulphate (Ag2SO4)

The crystal structures of silver(I) sulphate, Ag₂SO₄, have been investigated as a function of temperature. A main feature is the phase transition from the low‐temperature ordered phase, F ddd, to the high‐temperature disordered phase, . In particular, the high‐temperature structure is solved from single crystal synchrotron X‐ray measurements. In this phase the title compound undergoes a colossal (anisotropic) thermal expansion of . This is presumably owing to a high anisotropic vibration state of one of the two crystallographically independent Ag‐atoms. Simultaneously occurring high ionic conductivity may be associated with silver ions moving along the ‐axis using a “paddle‐wheel” assisted percolative mechanism. Onset of metallic silver in the single crystals is documented, seemingly dependent on thermal pre‐history, mosaic structure and chemical synthesis. Possible mechanisms explaining this effect, comprising disproportionation or photo‐decomposition, are suggested.     

Growth and Characterisation of (CuInTe2)1‐x(2 ZnTe)x Solid Solution Single Crystals

The crystal structure as well as the optical properties in the band gap region of (CuInTe₂)_1‐x(2 ZnTe)_x solid solution single crystals grown by directional freezing have been studied. The lattice constants exhibit a linear dependence on crystal composition. The chalcopyrite‐sphalerite phase transition was observed between x = 0.3 and x = 0.4°. The variation of the band gap with respect to crystal composition can be described by a quadratic expression.     

Thermal “order‐disorder” behaviour in (Na1‐xKx)4B8O14 solid solutions investigated by X‐ray powder diffraction

In the potassium‐rich part of the binary system Na₄B₈O₁₄‐K₄B₈O₁₄ solid solutions have been found that can be described with the formula (Na_1‐xK_x)₄B₈O₁₄ with 0.45 ≤ x < 1.0. The crystal structures of (Na_0.25K_0.75)₄B₈O₁₄ and (Na_0.45K_0.55)₄B₈O₁₄ were refined at room temperature by the Rietveld method. The solid solutions crystallize like K₄B₈O₁₄ in the triclinic crystal system, space group P ‐1, with K partially substituted for Na. An ordered distribution of the alkali atoms over the four cation sites at room temperature has been discovered. The structure of (Na_0.25K_0.75)₄B₈O₁₄ was also refined for data collected at 300 and 500 °C. The refinements show that sodium and potassium atoms are less ordered at higher temperatures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of PbxSr1‐x(NO3)2 Solid Solutions from Aqueous Solutions

A series of Pb_xSr_1‐x(NO₃)₂ crystals have been grown from aqueous solutions and characterized by X‐ray powder diffraction. All diffraction data were well indexed according to the simple cubic structure. The variation of lattice constants with the concentrations of Pb²⁺ in the crystals accorded quite well to the Vegard's Law. The composition of the Sr(NO₃)₂ crystal doped with Pb²⁺ was studied by electron microprobe and it was found that Pb²⁺ was enriched in the 111 sectors. Equilibrium behavior in the Pb(NO₃)₂‐Sr(NO₃)₂‐H₂O system was analyzed by Lippmann's phase diagram and the equilibrium distribution coefficient D_Pb=133.6. This large value of D indicates that Pb²⁺ ion is preferentially distributed to the solid phase.     

Thermal and optical properties of glasses of the system Bi2O3 – B2O3

In the binary system Bi₂O₃ – B₂O₃ glasses were prepared in the composition range 57.5 mol% ‐ 80 mol% B₂O₃ by defined slow cooling of large melt samples (about 75 cm³, each). Temperatures of crystallization, of melting and of glass transition were determined and density data of the glasses were derived using the hydrostatic weighting method. Thermal expansion coefficients and high precision refractive indices, together with their dispersion, were measured. The measured physical properties indicate subtle discontinuous structural changes of the glasses with glass composition, that match with the ranges of existence of the crystalline compounds of the binary system Bi₂O₃ – B₂O₃. Thermal investigations together with X‐ray powder diffraction analyses of crystallized glass samples prove the so far doubtful existence of a borate compound named “BiBO₃” in the PDF within the composition range 52.5 – 57.5 mol% B₂O₃.     

Controllable thermal expansion properties of In2 − xCrxMo3O12

Solid solutions In_{2 − x}Cr_xMo₃O₁₂ have been prepared via the solid state reaction method. The structural and thermal expansion properties have been characterized using X‐ray diffraction. All compounds exhibit monoclinic structure with space group P2₁/a at room temperature, and transform to orthorhombic structure at higher temperature. Compounds In_{2 − x}Cr_xMo₃O₁₂ (x = 0.7, 1.0 and 1.3) possess strong positive thermal expansion in the monoclinic structure, while their thermal expansion coefficients of orthorhombic structure vary from negative to positive with increasing Cr content. It is worthwhile to note that In_1.3Cr_0.7Mo₃O₁₂ and InCrMo₃O₁₂ have near zero thermal expansion properties.     

Phase diagram and single crystal growth of the CuInSe2xS2(1−x) solid solutions

The phase diagram of the CuInSe₂-CuInS₂ system is plotted using DTA and the solidus and liquidus lines by the approximation of the theory of regular and ideal solutions are calculated. The single crystals of the CuInSe_2xS_2(1−x) solid solutions are first grown by chemical transport.     

Optical properties of non‐centrosymmetric mixed crystals K2(La1‐x Cex)(NO3)5 · 2 H2O (x = 0.0 – 1.0)

Large single crystals of optical quality of the non‐centrosymmetric orthorhombic potassium rare earth nitrate mixed crystals K₂(La_1–x Ce_x)(NO₃)₅ · 2 H₂O were grown at 38 °C from diluted HNO₃. For crystals with x = 0.0, 0.19, 0.38 and 0.66 refractive indices and their dispersion were determined with an error less than 1 · 10^–4 in the wavelength range 0.404 – 1.083 μm by the prism method. Phase matching conditions for collinear SHG frequency conversion were analysed in detail, including calculation of the effective nonlinear optical susceptibility. By an appropriate choice of the fraction x of cerium the mixed crystals K₂(La_1–x Ce_x)(NO₃)₅ · 2 H₂O allow an adjustment of non‐critical type I phase matching conditions to a desired wavelength of the fundamental wave within the range 1.055(4) – 1.107(6) μm. Non‐critical type II phase matching can be tuned in the wavelength range 0.949(2) – 0.931(2) μm. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal expansion,pyroelectricity and linear optical properties of Li2SeO4·H2O and Li2SO4·H2O

Large single crystals of polar Li₂SeO₄·H₂O were grown at 343 K from aqueous solution. Temperature dependent thermal expansion coefficients of Li₂SeO₄·H₂O and Li₂SO₄·H₂O were determined within the temperature range 133 K–313 K and coefficients of the pyroelectric effect within the temperature range 183–343 K. Refractive indices between 365 nm and 1530 nm as well as unpolarized absorption spectra of Li₂SeO₄·H₂O and Li₂SO₄·H₂O were measured and phase‐matching curves for second harmonic generation were calculated. Both compounds allow type I and type II phase‐matching at wavelengths from about 650 nm to the near infrared region. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of big single crystals of Sr2YRu1‐xCuxO6 from high temperature solutions

Single crystals of Sr₂YRu_1‐xCu_xO₆ (x = 0 ‐ 0.4) have been grown from PbO‐PbF₂ based solutions in the temperature range 1150 – 1350°C. A silicon carbide heating element furnace (with a recrystallized alumina tube lining) in a vertical configuration was used to grow the crystals in platinum crucibles. Conditions for the stable growth of big crystals have been investigated. The morphology of the crystals containing Cu was found to change from octahedral to cube octahedral as the growth temperature is increased from 1150 to 1350°C. Crystals measuring up to 4.5 mm across and 2.5 mm thick have been grown from 1250°C. The incorporation of Cu into the crystals was ascertained by EDS and x‐ray diffraction analysis. A diamagnetic transition which increased in magnitude and temperature with x was observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)