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)     

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)     

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)     

Electron irradiation‐induced effects on optical spectra of (NH4)2ZnCl4: x Sr2+ single crystals

The effect of electron‐beam irradiation with different doses on optical constants of (NH₄)₂ZnCl₄: x Sr²⁺ crystals with x=0.000, 0.020, 0.039, 0.087 or 0.144 wt% has been studied. The optical transmission in the energy range 3.4‐6.4 eV was measured hence the absorption coefficient was computed as a frequency function. The absorption coefficient was also calculated as a function of electron‐beam dose. Irradiation with e‐beam did not affect the allowed indirect type of transition responsible for interband transitions of (NH₄)₂ZnCl₄: x Sr²⁺ crystals. Values of the optical energy gap E_g and optical moment E_p for electronic interband transition of unexposed and (NH₄)₂ZnCl₄: x Sr²⁺ crystals after e‐beam exposure were deduced. The area under the absorption band at 5.30 eV was used to evaluate the effect of e‐irradiation on optical parameters of samples with x=0.00, 0.020 or 0.039. A shift in the position and a nonmonotonic change in the intensity of this band with increasing e‐beam dose was observed. Changes in the E_g value were used to evaluate the effect of e‐beam exposure dose on (NH₄)₂ZnCl₄: x Sr²⁺ samples with x=0.087 or 0.144. The obtained results were compared with those obtained for the same crystals after irradiation with different γ‐doses.     

X‐ray diffraction analysis of powder and thin film of (Gd1‐x Yx)2O3 prepared by sol‐gel process

The mixed oxide (Gd_1‐xY_x)₂O₃ (0.0 ≤ x ≤ 1.0) were synthesized, as powder and thin film, by a sol‐gel process. X‐ray diffraction data were collected and crystal structure and microstructure analysis were performed using Rietveld refinement method. All samples were found to have the same crystal system and formed solid solutions over the whole range of x. The cationic distribution, Gd³⁺ and Y³⁺, over the two non‐equivalent sites 8b and 24d of the space group Ia3 is found to be random for all values of (x). The lattice parameter is found to vary linearly with the composition (x). Replacing Gd³⁺ and Y³⁺ by each other introduces a systemic decrease in the x‐coordinate of cation position (24d) and slight changes in the oxygen coordinates. Crystallite size and microstrain analysis is performed along different crystallographic directions and anisotropic changes are found with the composition parameter (x). The average crystallite size ranges from 75 to 149 nm and the r.m.s strain from 0.027 to 0.068 x10^‐2. Textured Gd_1.841Y_0.159O₃ (400) buffer layers, with a high degree of alignment in both out‐plane and in‐plan, are successfully grown on cube textured Ni (001) tape substrates by sol–gel dip coating process. The resulting buffer layers are crack‐free, pinhole‐free, dense and smooth. YbBa₂Cu₃O_7‐x (YbBCO) thin film could be (00l) epitaxially grown on the obtained buffer layer using sol–gel dipping technique. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal expansion and structural properties of (CuAlTe2)1–x(CuAlSe2)x solid solutions

Investigations of the thermal expansion of (CuAlTe₂)_1–x(CuAlSe₂)_x solid solutions in the temperature range from 100 to 800 K have been carried out for the first time. It has been demonstrated that the thermal expansion coefficient α_L grows considerably in the temperature range from 100 to 300 K, whereas the temperature dependence above 300 K is rather weak. The isotherms of composition dependence of the thermal expansion coefficient α_L for 100, 293, 500 and 800 K were constructed, and it was found that linear relations could express them. The Debye temperatures θ_D , the average mean‐square dynamic displacements , the average root‐mean‐square amplitudes of thermal vibration RMS , the anion position parameter u using S. C. Abrahams & J. L. Bernstein (u_AB ) and J. E. Jaffe & A. Zunger (u_JZ ) models were calculated. The composition dependence of microhardness H using the phenomenological theory was also calculated, and it was discovered that this dependence has a non‐linear character with a maximum of 383 kg/mm² at x=0.67. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Compositional dependence of morphology and lattice parameters during growth of K1‐x(NH4)xH2PO4 mixed crystals

Mixed crystals of ammonium dihydrogen phosphate and potassium dihydrogen phosphate K_1‐x(NH₄)_x H₂PO₄ were grown from aqueous solutions with x = 0.06, 0.09, 0.15, 0.32, 0.42, 0.51, 0.63, 0.70, 0.76, 0.78, 0.84, 0.88, 0.89 and 0.91. The crystal composition that differs from solution was estimated by X‐ray method. Morphology of the crystals changes from tetragonal prism to needles when the incorporation of either of the two components into the other; which also affects the growth rate along the prominent growth directions significantly. Growth along the [001] decreases initially with composition and reached the maximum when x = 0.5; whereas growth along the [100] always showed a decreasing trend with composition and attained a minimum value when x = 0.5. Crystal length along the [001] and [100] and aspect ratio are also compositional dependent. Unit cell parameters determined by X‐ray powder and single crystal analyses revealed that the ‘a ’ parameter shows only a small and linear variation but the ‘c ’ parameter changes significantly with ADP incorporation because of the difference in the effective ionic radius of K⁺ and NH₄⁺ ions and also the possibility of NH₄⁺ ion to form two different kinds of hydrogen bonds in the system. The existence of a pseudo‐cubic cell at the mixing composition x = 0.78 was also revealed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterisation of MoSexTe2−x (0 ⩽ x ⩽ 2) electrodes in terms of energetic location of valence and conduction bands

The layer type MoSe_xTe_2−x (0 ≦ x ≦ 2) has been grown by chemical vapour transport technique. The photoelectrochemical solar cells have been fabricated using the grown crystals as photoelectrodes and platinum grid as counter electrode in aqueous iodine/iodide solution. The optical band gap determination has been done from the study of the spectral response of the cells. The location of valence and conduction band edges and flat kind potentials have been evaluated using Mott-Schottky plots.     

Structure,microstructure and magnetic properties of mixed rare earth oxide (Dy1‐xErx)2O3

The mixed rare earth oxide (Dy_1‐xEr_x)₂O₃ (0.0 ≤ x ≤ 1.0) were synthesized by a sol–gel process. X‐ray and neutron diffraction data were collected and crystal structure and microstructure analyses were performed using Rietveld refinement method. All samples were found to have the same crystal structure and formed solid solutions over the whole range of x. Preferential cationic distribution is found for all samples but with different extent with Dy³⁺ preferring the 8b among the two non‐equivalent sites 8b and 24d of the space group Ia3. The lattice parameter is found to vary linearly with the composition x and a systematic variation is found in the r.m.s microstrain . Magnetization measurements were done in the temperature range 5‐300 K and a behavior in accordance with Curie‐Weiss law was found. Anomalous concentration dependence is found in magnetic susceptibility which is ascribed to the concentration dependence of effective crystal field combined with the contribution of ⁴I_15/2 and ⁶H_15/2 manifold at elevated temperature. The effective magnetic moments μ_eff is found to decrease linearly with composition parameter x, except for sample x=0.5 where the magnetization is enhanced. The Curie‐Weiss paramagnetic temperatures indicated antiferromagnetic interaction. These magnetic results are discussed in view of the cationic distribution. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and improved electrochemical performance of LiCo1‐xSnxO2 (x= 0 to 0.1) powders

Layered intercalation compounds LiCo_1‐xSn_xO₂ (x= 0 to 0.1) have been prepared using a simple combustion route method. X‐ray diffraction patterns and Laser Raman spectrum suggest that the synthesized materials had the R‐3m structure. Scanning electron images show that particles are well‐crystallized with a size distribution in the range of 50‐100 nm. The room temperature electrical conductivity of the sample increased with Sn content. For LiCo_1‐xSn_xO₂(x = 0, 0.01, 0.03, 0.05 and 0.1), the first discharge capacity increased with increase in Sn content. Among these samples, LiCo_0.95Sn_0.05O₂had produced the best performance of all others with a stable reversible capacity of 186 mAhg^‐1 after 30 cycles. (© 2010 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.     

Mild hydrothermal synthesis and structures of mixed‐valence iron phosphates: SrFe3(PO4)3 and the interesting Mg2+‐doped AFe3 (PO4)3 (A = Ba,Pb) in Fe2+ site

Series of mixed valence monophosphates AFe_3‐xMg_x(PO₄)₃ [A = Sr(x = 0), Ba(x = 0.6), Pb(x = 0.6)] were synthesized by mild hydrothermal treatment at 210 °C. Refinements of single crystal X‐ray diffraction datas show all these compounds are isostructural. The attempts to make AFe₃(PO₄)₃ (A = Ba, Pb) hydrothermally in the experiment were unsuccessful. However, the Mg‐doped homologues AFe_2.4Mg_0.6(PO₄)₃ (A = Ba, Pb) were synthesized with the addition of MgCO₃ in the reactants as mineralizer. EDS and single crystal X‐ray data refinement indicated that the Mg²⁺ cations were doped in the Fe²⁺ sites of AFe_2.4Mg_0.6(PO₄)₃ (A = Ba, Pb). The influence of the Mg‐doping on the structure and the reason why the Mg doped in the Fe(II) site instead of A site was discussed from the point of view of the bond valence model.     

Electrical and dielectric behavior of the system Gd1‐xBaxCoO3 (x = 0.00, 0.10, 0.20) synthesized by chemical route

The samples in the system Gd_1‐xBa_xCoO₃ (x = 0.00, 0.10, 0.20) were prepared by chemical route. These samples form single‐phase materials, which were confirmed by XRD and TGA studies. The presence of interfacial polarization is responsible for high value of dielectric constant in these materials. The conductivity observed in Gd_1‐xBa_xCoO₃ system may be due to mobile holes created by excitation of an electron from the π* band to an acceptor level.     

Structural,optical and electrical characterization of HgxCd1‐xTe polycrystalline films fabricated by two‐source evaporation technique

Two‐source thermal evaporation technique was used to prepare Hg_xCd_1‐xTe thin films onto scratch free transparent glass substrates. The structural investigations revealed that thin films were polycrystalline in nature. Transmittance measurements in the wavelength range (500‐2700 nm) were used to calculate optical constants. The analysis of the optical absorption data showed that the optical band gap was of indirect type. In the composition range 0.05 < x < 0.25 the films exhibited an optical band gap between 1.29 and 0.98 eV. In the same composition range the films were p‐type and exhibited a resistivity, which varied between 10² and 10^‐1 Ω‐cm. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical properties of PbxSn1‐xS thin films prepared by hot wall deposition method

The Pb_xSn_1‐xS (x = 0 – 0.25) thin films were prepared on glass substrates by hot wall vacuum deposition. The films were polycrystalline monophase in nature and had orthorhombic crystal structure. The thickness of the films was about 2‐3 μm. The temperature dependences of the conductivity were measured in the temperature range from 150 to 420 K. The films revealed p‐type of conductivity. The Seebeck coefficient and conductivity values of the films was in the range of α = 6 – 360 μV/K and σ = 4.8×10^‐5 – 1.5×10^‐2 Ω^‐1·cm^‐1, respectively, at room temperature depending on concentration of the lead in the films. The lead atoms created the substitution defects Pb_Sn in the crystal lattice of the Pb_xSn_1‐xS. These defects formed the donor energy levels in the band gap. The activation energy of the films increased in the range ΔE_a = 0.121 – 0.283 eV with increasing of the lead concentration. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of indium intercalation on various properties of MoSe2 single crystals

Indium intercalated MoSe₂ single crystals i.e. In_xMoSe₂ (0 ≤ x ≤ 1) are grown by direct vapour transport technique. These crystals are structurally characterized by X‐ray diffraction, by determining their lattice parameters ‘a’ and ‘c’ and X‐ray density. The Hall effect and thermoelectric power measurements shows that In_xMoSe₂ (0 ≤ x ≤ 1) are p‐type in nature. The direct and indirect band gap measurements are also undertaken on these semiconducting materials. (© 2007 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)     

Effective electro‐optic coefficient of (1–x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 single crystals

Refractive indices and effective electro‐optic coefficient γ_c of (1–x)Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ (PZN‐xPT, x = 0.05, 0.09 and 0.12) single crystals were measured at 532 nm wavelength. Orientation and temperature dependences of the electro‐optic coefficient were investigated. Large electro‐optic coefficient (γ_c = 470 pm/V) was observed in [001]‐poled PZN‐0.09PT crystal. More importantly, γ_c of tetragonal PZN‐0.12PT is almost unchanged in a temperature range −20 ∼ 80 °C. The γ_c of PZN‐xPT single crystals are much higher than that of widely used electro‐optic crystal LiNbO₃ (γ_c = 20 pm/V). These results show that PZN‐xPT single crystals are very promising materials for electro‐optic modulators in optical communications.     

CuxAg1–xGaS2 Solid Solutions

Cu_xAg_1–xGaS₂ large-scale blocks were obtained by two-temperature synthesis method with the following crystallization of the melt. It was established, that crystal lattice parameters are changed according with Vegard's law, and microhardness have an extremum on the base DTA measurements state diagram of AgGaS₂ CuGaS₂ system was built up. The composition dependence of band gap has nonlinear behaviour.     

Structural,optical and photoconductive properties of electron beam evaporated CdSxSe1‐x films

CdS_xSe_1‐x films were deposited by the electron beam evaporation technique on glass substrates at different temperatures in the range 30 – 300 °C using the laboratory synthesized powders of different composition. The films exhibited hexagonal structure and the lattice parameters shifted from CdSe to CdS side as the composition changed from CdSe to CdS side. The bandgap of the films increased from 1.68 to 2.41 eV as the concentration of CdS increased. The root‐mean‐roughness (RMS) values are 3.4, 2.6, 1.2 and 0.6 nm as the composition of the films shifted towards CdS side. The conductivity varies from 30 Ωcm^‐1 to 480 Ωcm^‐1 as the ‘x’ value increases from 0 to 1. The films exhibited photosensitivity. The PL spectrum shifts towards lower energies with decreasing x, due to the decrease of the fundamental gap with Se composition. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)