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)     

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)     

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)     

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.     

Crystal growth of zirconium‐doped KTiOPO4 crystals in the K2O‐P2O5‐TiO2‐ZrF4 system

Zirconium‐doped KTiOPO₄ (KTP) crystals were grown using a high temperature flux method in the K₂O‐P₂O₅‐TiO₂‐ZrF₄ system. The dopant content in the single crystals with general composition KTi_1‐xZr_xOPO₄ (where x = 0 – 0.026) strongly depends on zirconium concentration in the homogeneous melts. AES‐ICP method and X‐ray fluorescence analysis were used to determine the composition of the obtained crystals. Phase analyses of the products were performed using the powder XRD. The structures of KTiOPO₄ containing different quantities of Zr were refined on the basis of single crystal XRD data. Applying ZrF₄ precursor for zirconium injection into the flux allowed growing the zirconium‐doped KTP crystals at 930–750°C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth,structure, and superconducting properties of Bi2Sr2Ca2Cu3O10 and (Bi,Pb)2Sr2Ca2Cu3O10‐y crystals

Large and high‐quality single crystals of both Pb‐free and Pb‐doped high temperature superconducting compounds (Bi_1‐xPb_x)₂Sr₂Ca₂Cu₃O_10‐y (x = 0 and 0.3) were grown by means of a newly developed “Vapour‐Assisted Travelling Floating Zone” technique (VA‐TSFZ). This modified zone‐melting technique was realised in an image furnace and allowed for the first time to grow Pb‐doped crystals by compensating for the Pb losses occurring at high temperature. Crystals up to 3×2×0.1 mm³ were successfully grown. Post‐annealing under high pressure of O₂ (up to 10 MPa at T = 500°C) was undertaken to enhance T_c and improve the homogeneity of the crystals. Structural characterisation was performed by single‐crystal X‐ray diffraction (XRD) and the structure of the 3‐layer Bi‐based superconducting compound was refined for the first time. Structure refinement showed an incommensurate superlattice in the Pb‐free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 27.105(4) Å, b = 5.4133(6) Å and c = 37.009(7) Å. Superconducting studies were carried out by A.C. and D.C. magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (ΔT_c ≤ 1 K). In optimally doped Pb‐free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2�10⁵ A/cm² were measured at T = 30 K and μ₀H = 0 T. A weak second peak in the magnetisation loops was observed in the temperature range 40‐50 K above which the vortex lattice becomes entangled. We have measured a portion of the irreversibility line (0.1‐5 Tesla) and fitted the expression for the melting of a vortex glass in a 2D fluctuation regime to the experimental data. Measurements of the lower critical field allowed to obtain the dependence of the penetration depth on temperature: the linear dependence of λ(T) for T < 30 K is consistent with d‐wave superconductivity in Bi‐2223. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

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)     

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.     

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)     

Some structural considerations on the perovskite‐type A1‐ySryCo1‐xFexO3‐δ solid solution series

Solid solution series of La_1‐ySr_yCo_1‐xFe_xO_3‐δ were extensively studied in the past as cathode materials for solid oxide fuel cells. However, the crystal structure behavior of La_1‐ySr_yCo_1‐xFe_xO_3‐δ solid solution series when La‐ions are replaced with another rare‐earth ion or metallic alkaline earth metal is at present not fully understood. Here we report X‐ray powder diffraction measurements performed on samples of the Sm_0.8Sr_0.2Co_1‐xFe_xO_3‐δ solid solution series. This study demonstrates that the average A‐cation radius, as well as the Fe content (x), affects the structural modification of the A_1‐ySr_yCo_1‐xFe_xO_3+δ solid solution series significantly. (© 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)     

Crystal growth,optical and luminescence properties of (Ce,Sr)‐doped PrAlO3 single crystals

Using the micro‐pulling‐down method, (Ce,Sr)‐doped PrAlO₃ square‐shaped single crystals (4×4×12 mm) were grown. Structural parameters studied by X‐ray powder diffraction were consistent with R3m space group. Compositional homogeneity was checked with electron probe micro‐analysis and found quite uniform. Absorption spectra and luminescence characteristics under UV and X‐ray excitations were measured at room temperature with no Ce‐related emission appeared. (© 2007 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)     

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)     

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)     

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)     

Structural,thermal, mechanical and z‐scan studies on 4‐nitrophenol single crystals

4‐nitrophenol (4‐NP) single crystals have been grown by using slow evaporation and slow cooling techniques. A single crystal with size in the range of 7x3.4x1.8cm³ has been obtained by slow cooling method. The grown crystals have been subjected to various characterization studies. The powder XRD spectrum of 4‐NP reveals the good crystalline nature of the grown crystal. Single crystal XRD studies show that the crystal belongs to monoclinic system with cell parameters of a=6.09 Å, b=8.79 Å, c=11.61 Å, α=γ=90°, β=103.15°. The resultant FTIR spectrum confirms the various functional groups present in 4‐NP. Thermal analysis has been performed on the material to study the thermal stability of 4‐NP. The grown crystals belong to the category of soft materials as confirmed by Vickers Hardness tests. The optical transmiitance of 4‐NP single crystals has been measured from Vis‐IR spectroscopy study. The nonlinear optical properties have been analyzed by z‐scan technique and 4‐NP is found to be self defocusing because of its negative nonlinear refractive index. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrochemical growth and properties of LaMn1−xCoxO3 (0 < x ≤ 1) single crystals

Single crystals of LaMn_1−xCo_xO₃ (0 < x < 1) with distorted perovskite structure have been obtained by the electrodeposition technique at anode from flux melt using Cs₂MoO₄‐MoO₃ binary system as solvent. An investigation of magnetic and electrical properties of the obtained crystals as well as its comparison with those for ceramic samples of the same composition were carried out. A much weaker interplay between magnetic and electrical properties and a smaller ∼8% magnetoresistance were found in the ternary oxide crystals slightly doped by Co on the verge of transition to ferromagnetic state in comparison to the data have been reported for LaMnO_3+δ single crystals. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth process and optical investigations of Nd:NaGd (MoO4)2 crystals with varying content of Nd and Gd

In this paper, [NaGd_1‐xNdx](MoO₄)₂ crystals with x = 0.005–0.05 were grown by Czochralski method at 950 ℃ for 10 hours and subsequently characterized by absorption spectroscopy and fluorescence spectroscopy. The intensity parameters of Nd³⁺ were calculated by Judd‐Ofelt theory, and the relationship between the parameters and Nd³⁺ concentration was analyzed. The results show that with the increasing Nd³⁺ concentration, the oscillator strength, stimulated emission cross‐section, Ω_t and spontaneous transition probability decrease slightly, while the fluorescence lifetime decreases significantly. However, the fluorescence branching ratio is almost unchanged with the increasing Nd³⁺concentration. The [NaGd_1‐xNd_x](MoO₄)₂ crystal with (x = 0.01) possesses the highest quantum efficiency of 88.98%, a good fluorescence line‐width of 23 nm, a large value of σ_em·τ_f up to 0.55 × 10⁻²² cm²·s and a stimulated emission cross‐section up to 3.747 × 10⁻¹⁹ cm² for the transition from ⁴F_3/2 to⁴I_11/2 at 1064 nm. Test results indicate that [NaGd_1‐xNd_x](MoO₄)₂ crystals are an excellent gain media for the solid state laser system.