Phase equilibria in BaB2O4–LiF system and β–BaB2O4 bulk crystals growth

Solid state synthesis, differencial thermal analysis and visual polythermal analysis were applied to study the phase equilibria in BaB₂O₄–LiF system. A phase diagram BaB₂O₄–LiF has been plotted for the first time. The system has proved applicable for growing β–BaB₂O₄ bulk crystals.     

Nonstoichiometry of the New Laser Host LiCaAlF6

LiCAF (LiCaAlF₆) and LiSAF (LiSrAlF₆) single crystals were grown by the Czochralski technique. DTA measurements of the grown crystals and of different mixtures within the ternary systems LiF—Me^IIF₂—AlF₃ (Me^II = Ca, Sr) lead to the conclusion, that LiCAF melts incongruently with a deficiency of CaF₂. For LiSAF congruent melting and no deviation from the ideal stoichiometry could be observed. From DTA results the enthalpies of fusion were determined: ΔH_LiCAF ≈︂ 110 kJ/mol, ΔH_LiSAF ≈︂ 80 kJ/mol. The circumstance, that LiSAF crystals are usually reported to have much better optical properties in comparison to LiCAF is attributed to these differences in the thermodynamic behaviour.     

Defect structure and spectroscopic characteristics of codoped Hf: Er: LiNbO3 crystals

Codoped Hf: Er: LiNbO₃ crystals have been grown by the Czochralski technique. Defect structures of the crystals were analyzed by IR absorption spectra, and the compositions of the crystals were measured by X‐ray fluorescent spectrograph. A new OH^–‐associated vibrational peak at 3492 cm^–1 was revealed in 6 mol % Hf: 1 mol % Er: LiNbO₃ crystal. It was attributed to (Hf_Nb)^–‐OH^–‐(Er_Nb)^2– defect centers. The Er³⁺ concentrations in crystals gradually decreased with the increase of the codoped Hf⁴⁺ concentrations in the melts. The emission characteristics of the crystals were investigated by the fluorescence spectrum. It was found that the luminescent intensity in codoped 6 mol % Hf: 1 mol % Er: LiNbO₃ crystal was 3.5 times stronger than that in single doped 1 mol % Er: LiNbO₃ crystal. The luminescent enhancement effect was successfully explained on the basis of defect structure of the crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Second Harmonic Generation in Zn‐doped Li‐rich LiNbO3 Crystals

6.0 mol. % ZnO doped LiNbO₃ crystals were grown by Czochralski technique. Various Li/Nb mole ratios of 0.942, 0.970, 1.000, and 1.020 were used to prepare the starting materials. Second harmonic generation (SHG) experimental results show that the phase matching temperature increases near linearly with the increasing of Li/Nb ratio, and the SHG efficiency is enhanced by the Zn doping and the increasing of Li/Nb ratio. The intrinsic and extrinsic defects are discussed in this paper to explain the SHG behavior and photo‐damage resistance in the Zn doped Li‐rich LiNbO₃ crystals.     

X‐ray diffraction and magnetization studies of BiFeO3 multiferroic compounds substituted by Sm3+, Gd3+, Ca2+

The multiferroic compounds Bi_0.9Sm_0.1FeO₃, Bi_0.9Gd_0.1FeO₃, Bi_0.9Ca_0.1FeO₃, Bi_0.9Sm_0.05Ca_0.05FeO₃, and Bi_0.9Gd_0.05Ca_0.05FeO₃ were prepared by the conventional ceramic method and were characterized by X‐ray diffraction, vibrating sample magnetometry, and differential scanning calorimetry. The compounds were found to have the rhombohedral perovskite‐like structure, accompanied by a small residual Bi₂Fe₄O₉ impurity phase. Magnetic hysteresis loops with enhanced remnant magnetization and coercive field were obtained for the Gd‐containing compounds. The improvement of magnetic behavior of the Gd‐containing compounds is thought to arise mainly from the partial suppression of the spiral spin structure and the stronger interaction between magnetic ions. The magnetic transition temperatures of the compounds were found to be in the range 300‐310 °C. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

Effect of γ-irradiation on mechanically activated and on non-activated LiF

By means of EPR spectroscopy lattice defects have been investigated, which had been produced in OH⁻ containing LiF by mechanical activation and subsequent irradiation (mainly γ-irradiation). The structure of irradiation-induced hydrogen centers shows characteristic differences dependent on the kind of LiF: H_s⁰ (hydrogen atoms in anion vacancies) are created in mechanically activated LiF powders, whereas H_i⁰ (hydrogen atoms in interstitial positions) in LiF single crystals. In both the cases also F centers are produced besides other paramagnetic defects. The observed defects can be used for an estimation of the degree of distortion in mechanically activated LiF.     

Growth and characterization of large La1‐xPbxMnO3+δ (x=0.32–0.35) crystals

Large crystals of La_0.63Pb_0.37Mn O_3+δ with small La(Pb)‐ deficiency of about 0.005‐0.01 at.% were grown by high temperature solution growth method. The structure of the grown crystals was determined as rhombohedral with R‐3 space group by single‐crystal X‐ray diffractometry. The surface morphology of the crystals and the exact chemical composition was examined by scanning electron microscopy and energy dispersive X‐ray analysis methods, respectively. The IR‐transmission spectrum reveals the presence of Mn³⁺O₆‐ and Mn⁴⁺O₆‐ octahedra in the lattice of La_0.63Pb_0.37Mn O_3+δ crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Calorimetric and phase equilibria studies of the Ni–Sn–Bi system

The phase equilibria at 1273 K were investigated and an isothermal section of the Ni‐Sn‐Bi phase diagram was constructed. The phase boundaries are inclined to the Bi‐rich region that is agreement with phase equilibria at lower temperatures. The molar enthalpies of formation of liquid ternary Ni–Sn–Bi alloys have been determined at 833, 873 and 933 K by direct reaction calorimetry using pellets of 325 mesh powders of pure Ni, Sn and Bi. Measurements were performed with alloys containing from 0.05 to 0.10 mole fractions of nickel, and at ratios of tin and bismuth mole fractions X_Sn/X_Bi = 2.8, 1.2 and 0.43. The experimental calorimetric data were used to calculate a regular solutions parameter of the ternary liquid phase by means of two different thermodynamic data files. It was found that the Ni–Sn–Bi ternary liquid phase could be described as temperature independent ternary regular solution. The assessed values of the ternary interaction parameter are ‐280 J·mol^–1 and 56 000 J·mol^–1, depending on the binary parameters used. Enthalpies of formation of solid binary phases were measured, too. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of LaBGeO5 crystal fibers by the micro‐pulling down technique

The LaBGeO₅ compound (LBGO) was prepared by solid state reaction at 1050°C and characterized by XRD and DTA analysis. The direct growth of LBGO fibers from the melt using micro‐pulling down technique was unsuccessful because of its high viscosity. The study of the LBGO‐LiF phase diagram showed that LiF could be considered as a convenient flux to reduce viscosity of the melt during the growth process. Several crystal fibers were then grown and characterized by Raman spectroscopy. To decrease the high volatility of LiF, B₂O₃ was added to the melt. A white cloudy fiber was obtained from LiF‐B₂O₃ flux and checked by Raman spectroscopy and scanning electron microscopy.     

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)     

Structure and Photo‐Damage Resistance of Li‐Rich LiNbO3 Crystals Co‐Doped with Zn2+/Er3+

The pure congruent LiNbO₃, Er:LiNbO₃ and Zn,Er co‐doped Li‐rich LiNbO₃ crystals were grown by Czochralski method. The X‐ray diffraction method and ultraviolet‐visible absorption spectra of the crystals were used to analyze the structure of the crystals. The photo‐damage ability resistance of the crystals was measured. The Zn,Er co‐doped Li‐rich LiNbO₃ crystals show a decrease in lattice constant values, a shift in absorption edge of ultraviolet‐visible absorption spectra towards shorter wavelength, and three orders of magnitude increase in photo‐damage resistance compared to congruent LiNbO₃ crystal. The intrinsic and extrinsic defects are discussed to explain the enhance of the photo‐damage ability resistance     

Transparent phosphosilicate glasses containing crystals formed during cooling of melts

Effect of P₂O₅–SiO₂ substitution on spontaneous crystallization of SiO₂–Al₂O₃–P₂O₅–Na₂O–MgO melts during cooling was studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and rotation viscometry. Results show that addition of P₂O₅ leads to amorphous phase separation (APS), i.e., phosphate- and silicate-rich phases. It is due to the tendency of Mg²⁺ to form [MgO₄] linking with [SiO₄]. Molar substitution of P₂O₅ for SiO₂ enhances the network polymerization of silicate-rich phase in the melts, and thereby the spontaneous crystallization of cubic Na₂MgSiO₄ is also enhanced during cooling of the melts. In addition, the sizes of the local crystalline and separated glassy domains are smaller than the wavelength of the visible light, and this leads to the transparency of the obtained glasses containing crystals.     

Compositional variation in 0.65 PbMg2/3Nb1/3O3 ‐0.35 PbTiO3 single crystals grown by high temperature solution growth technique

Single crystals of lead magnesium niobate titanate, 0.65 PbMg_2/3Nb_1/3O₃ (PMN) ‐0.35PbTiO₃ (PT) were grown using flux method near morphotropic phase boundary (MPB) composition. The crystals grown at the centre of the platinum crucible were found to PT deficient compared to those grown near the walls of the crucibles. A variation of ∼3.8 mol% in PT concentration was found in the crystals grown at the wall and at the centre of the crucible. The difference in the chemical composition of crystals grown at the centre and the near the wall of the crucible was observed by X‐ray diffraction, EDXRF, dielectric and thermal measurements. The presence of PT rich and deficient crystals is explained in terms of the segregation coefficient of PT in PMN. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Re‐determination of the pseudobinary system Li2O – MoO3

The quasi‐binary phase diagram lithium oxide – molybdenum(VI) oxide was investigated by differential scanning calorimetry and X‐ray diffraction. The four intermediate phases Li₄MoO₅, Li₂MoO₄, Li₄Mo₅O₁₇, and Li₂Mo₄O₁₃ show incongruent melting. The system has one eutectic point at 50.5 mol% MoO₃ and 49.5 mol% LiO_0.5 with a eutectic temperature of 524.6°C. At this point the melt is in equilibrium with Li₂MoO₄ and Li₄Mo₅O₁₇. (© 2008 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)     

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.     

Growth of CuInS2 single crystals from Sb2S3 and Bi2S3 solutions

The phase diagrams of the CuInS₂‐Sb₂S₃ and CuInS₂‐Bi₂S₃ systems were investigated using X‐ray powder diffraction and differential thermal analysis. Based on these results, the compositions for the growth of the CuInS₂ single crystals from CuInS₂‐Sb₂S₃ and CuInS₂‐Bi₂S₃ melts were selected and Bridgman crystal growth process was performed. The investigation of the obtained single crystals using X‐ray powder diffraction and optical absorption spectra indicates that the incorporation of the solvent atoms into the crystal lattice is absent. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature-concentration fields of the crystallization of YbAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> from high-temperature melt solutions based on potassium trimolybdate

The phase relationships in the YbAl₃(BO₃)₄-K₂Mo₃O₁₀-B₂O₃-Yb₂O₃ multicomponent system are investigated in the temperature range 1150–1000°C within the stability region of the YbAl₃(BO₃)₄ compound. The region of single-phase crystallization of the YbAl₃(BO₃)₄ borate is revealed in the section corresponding to the composition containing 15 wt % YbAl₃(BO₃)₄. For the same composition, it is demonstrated that there exists a correlation between the temperatures of saturation of melt solutions with the YbAl₃(BO₃)₄ borate and the composition of the solvent, namely, the contents of B₂O₃, K₂Mo₃O₁₀, and Yb₂O₃ in the solvent. The temperature dependences of the solubility of the YbAl₃(BO₃)₄ compound at different contents are determined for melts of two compositions: melt I containing 55 mol % K₂Mo₃O₁₀ and 45 mol % B₂O₃ and melt II containing 55 mol % K₂Mo₃O₁₀, 40 mol % B₂O₃, and 5 mol % Yb₂O₃. The specific features of the crystallization of the YbAl₃(BO₃)₄ compound are analyzed and compared with those of the yttrium, neodymium, gadolinium, and erbium aluminum borates studied previously.