X‐ray studies on quaternary system RbXK1‐XBrYCl1‐Y

Single crystals of the quaternary crystalline solid solution system Rb_xK_1‐xBr_yCl_1‐y have been grown by melt technique for three different compositions y = 0.25, 0.50 and 0.75, keeping x = 0.5 and X‐ray diffraction studies have been carried out for each case independently, using spherically ground single crystals. The results indicate an enhancement of Debye‐Waller B(total) factors for the compositions y = 0.25 and 0.75 whereas for the intermediate composition, y = 0.5, the factor B(total) is close to the end member value. This experimental investigation show that for this composition, the crystalline solid solution behaves like an end member crystal.     

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)     

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)     

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)     

Microwave dielectric properties of (1‐x)La(Mg0.5Sn0.5)O3‐x(Sr0.8Ca0.2)3Ti2O7 ceramic system with a near zero temperature coefficient of resonant frequency

In this study, the microwave dielectric properties of (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system prepared by the conventional solid‐state method have been investigated for application in mobile communication. It was found that the diffraction peaks of (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system shift to higher angles as x increases from 0.2 to 0.4. It was also found that the X‐ray diffraction patterns of the 0.8La(Mg_0.5Sn_0.5)O₃‐0.2(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramics exhibited no significant phase difference at different sintering temperatures. The average grain size of the (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system decreased from 6.4 to 4.3 μm as the value of x increased from 0.2 to 0.4 sintered at 1550 °C for 4 h. The dielectric constant increased from 26.6 to 35.9 and the quality factor (Q×f) decreased from 31,600 to 23,300 GHz for (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system as the x value increases from 0.2 to 0.4 sintered at 1550 °C for 4 h. The average value of temperature coefficient of resonant frequency (τ_f) increased from ‐18 to +8 ppm/ K as the x value increases from 0.2 to 0.4. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

Effect of rapid thermal annealing on Zn1‐xCdxO layers grown by radio‐frequency magnetron co‐sputtering

Zn_1‐xCd_xO layers were deposited on the sapphire substrate using the radio‐frequency magnetron co‐sputtering system. The grown Zn_1‐xCd_xO layers were carried out in the post‐annealing treatment for 1 min at the 800 °C oxygen‐ambient by the rapid thermal annealing (RTA) method. X‐ray diffraction (XRD) experiment shows that the Zn_1‐xCd_xO layers are changed from the single phase of the hexagonal structure at 0≤x ≤0.08 to the double phase of hexagonal‐and‐cubic structure at x =0.13. Thus, the maximum Cd‐composition ratio with the hexagonal structure was found out to be x =0.08. Also, the crystallinity of Zn_1‐xCd_xO layers at x =0.13 was remarkably improved by the RTA annealing treatment. This crystal quality improvement was thought to be associated with the relaxation of the compressive strain remaining in the Zn_1‐xCd_xO layers. Therefore, the results of XRD and transmittance lead that the crystal quality of the Zn_1‐xCd_xO layers forming the hexagonal ZnO phase is better than that forming the cubic CdO phase. Consequently, the reliable formation and the crystallinity of the Zn_1‐xCd_xO layers were achieved by using the RTA method of short‐time thermal‐annealing at the high temperature. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of annealing and composition on crystal structure,surface morphology and optical absorption of chemically deposited Cd1‐xSnxS films

Cd_1‐xSn_xS thin films were successfully deposited on suitably cleaned glass substrate by chemical bath deposition method at 74 °C. Hydrated Stannous Chloride (SnCl₂.2H₂O) in aqueous solution was added to the CdS growing solution in different proportions. The experimental results indicate, a successful doping for lower concentration of Sn, saturation for intermediate doping levels, and a degradation of the doping process for higher concentration of Sn. Indirect (X‐ray diffraction) and Direct (Scanning electron microscopy) measurements were performed to characterize the growth and the nature of crystallinity of the different Cd_1‐xSn_xS films. The effect of annealing on the crystal structure and morphology of the deposited films has also been discussed. The X‐ray diffraction spectra show that the thin films are polycrystalline and have both cubic and hexagonal structure. The Interplanar spacing, lattice constant, grain size, strain, and dislocation density were calculated for as‐deposited and annealed films. The grain size was found to decrease from 5 nm to 0.89 nm with doping concentration of Sn. The grain size further decreased due to annealing at 400 °C. SEM studies show layered growth and long needle like structures along with some voids. After annealing the densification and smaller size of the particles was also observed. The optical absorption spectra show shifting of absorption peaks towards lower wavelength side (© 2010 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)     

X‐ray powder diffraction study of the semiconducting alloy Cu2Cd0.5Mn0.5GeSe4

The structure of the semiconducting alloy Cu₂Cd_0.5Mn_0.5GeSe₄ was refined from an X‐ray powder diffraction pattern using the Rietveld method. The present alloy crystallizes in the wurtz‐stannite structure, space group Pmn2₁ (N^o 31), and unit cell parameters values of a = 8.0253(2) Å, b = 6.8591(2) Å, c = 6.5734(2) Å and V = 361.84(2) ų. The structure exhibits a three‐dimensional arrangement of slightly distorted CuSe₄, Cd(Mn)Se₄ and GeSe₄ tetrahedras connected by corners. © 2004 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)     

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)     

Multimode phonon structure of Be‐containing II ‐ VI mixed crystals determined by IR spectroscopic ellipsometry

Spectroscopic ellipsometry in the infrared spectral range 250‐5000 cm^‐1 is used for analysis of the dielectric response of Zn_1‐x‐yBe_xMg_ySe and Zn_1‐x‐yBe_xMn_ySe crystals grown by a high‐pressure Bridgman method. Ellipsometric spectra display features in the spectral range 390‐500 cm^‐1 associated with BeSe‐type phonon modes. In the optical spectra of Zn_1‐x‐yBe_xMg_ySe crystals both BeSe‐type and MgSe‐type lattice absorption bands are detected. The MgSe‐like modes are located at approximately 300 cm^‐1. The complex dielectric functions can be reproduced using a model with two or three and one or two classical damped oscillators corresponding to the BeSe‐like and the MgSe‐like transverse‐optical phonon modes, respectively. The frequencies of longitudinal‐optical phonons have been derived from the dielectric loss functions. A red‐shift of the BeSe‐like phonons frequencies with a mean rate 0.42 cm^‐1 (0.50 cm^‐1) per mole percent of Mg (Mn) incorporated to the alloy has been found for examined concentration range x, y ≤ 0.25. A noticeable damping the intensities of BeSe‐type modes with increasing fraction of Mg and Mn dopant is observed in comparison to the strengths of BeSe‐type modes in Zn_1‐xBe_xSe crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural properties of Zn1–xMgxO nanomaterials prepared by sol‐gel method

The mixed oxides Zn_1‐xMg_xO (ZMO) were prepared as nano‐polycrystalline powders and thin films by a simple sol–gel process and dip coating method. Thermogravimetric (TG) and differential thermal analysis (DTA) were used to study the thermal chemistry properties of dried gel. Structural and microstructural analysis was carried out applying x‐ray diffraction (XRD) and Rietveld method. Analysis showed that for x < 0.25, Mg replaces Zn substitutionally yielding ZMO single phase, while for x ≥ 0.25 two phases are identified ZMO and MgO. Replacing Zn²⁺ by Mg²⁺ distorts the cation tetrahedrons and decreases the lattice constants ratio c/a of the wurtzite ZMO which deviate the lattice gradually from the hexagonal structure as Mg⁺² increases. These distortions are attributed to the difference in electronic configuration of the two cations which suppress the paraelectric‐ferroelectric phase transition in the ZMO wurtzite. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase transformation in the system TlBi(Te1‐xSex)2

TlBiTe₂ and TlBiSe₂ ‐ that are ternary analogs of the IV‐VI semiconductors ‐, although they crystallize in the same space group R m (D⁵_3d), exhibit different behaviour during heating. The observed phase transformation depends on Se content (x) in the system TlBi(Te_1‐xSe_x)₂ and the transformation disappears by increasing Se content after a certain value (x = 0.25). This dependence is examined through the analysis of the DSC non‐isothermal measurements and an attempt for the explanation of the observed behaviour is undertaken through the consideration of off‐center atoms. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

Microwave dielectric properties of La(1‐2x/3)Bax(Mg0.5Sn0.5)O3 ceramics

This study examined the potential applications of microwave dielectric properties of La_(1‐2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ ceramics in rectenna. The La_(1‐2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid‐state method with various sintering temperatures. An apparent density of 6.62 g/cm³, a dielectric constant of 20.3, a quality factor of 51,700 GHz, and a temperature coefficient of resonant frequency of ‐78.2 ppm/K were obtained for La_2.98/3Ba_0.01(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Incorporation of hafnium (IV) into KTP framework from phosphate‐fluoride fluxes

Solid solutions KTi_1‐XHf_XOPO₄ (х = 0.008 – 0.107) possessing the KTiOPO₄ structure, have been synthesized in molten system K₂O‐P₂O₅‐TiO₂‐HfF₄. The crystal growth experiment of Hf‐doped KTP crystal has been reported. The X‐ray powder diffraction data and chemical analysis are also presented. It has been shown that KTiOPO₄ crystal structure slightly changes when Hf incorporates into the framework. Transmission/absorption spectra of KTi_0.974Hf_0.026OPO₄ crystals have been recorded. The incorporation of Hf ions shifts the optical absorption edge in the UV‐visible spectrum towards the long‐wavelength region with absorption near 387 nm.     

Growth and photoluminescence properties of CdS solid solution semiconductor

Photoluminescence (PL) emitted from Cd_1‐xZn_xS and CdS_1‐ySe_y solid solution semiconductor was significantly stronger than PL from the pure CdS and CdSe semiconductor. The samples were prepared using an improved Se‐S‐Na₂S flux route. Photoluminescence in Cd_1‐xZn_xS crystal was brightly yellow at the room temperature under VU radiation. The phase and composition of the solid solution was measured by the XRD and was confirmed by UV‐NIS spectrum as x of 0.3 and y of 0.2. The enhanced photoluminescence was presumably due to the introduction of extra defect (vacancies) by solid solution action and consequently the increasing of luminescence center concentration. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of II –VI alloy lattice dynamics by IR spectroscopic ellipsometry

Optical properties related to lattice vibrations of bulk Zn_1‐xBe_xSe, Zn_1‐x‐yBe_xMn_ySe and Cd_1‐xBe_xSe alloys are reported. Optical phonons of the mixed crystals grown by the Bridgman method have been investigated by infrared spectroscopic ellipsometry in the wave‐number range 300‐8000 cm^‐1. The complex dielectric functions can be reproduced using a model with two or three classical damped oscillators corresponding to the BeSe‐like transverse‐optical phonon‐modes and a Drude contribution from the free carriers. The frequencies of longitudinal‐optical phonons have been found from the imaginary parts of the dielectric loss functions. The influence of the alloy composition on the zone‐centre optical phonon frequencies is discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)