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)     

Synthesis and single crystal X‐ray structure of the tetragonal tungsten bronze Pb0.91K1.72Li1.46Nb5O15

Crystals of Pb_0.91K_1.72Li_1.46Nb₅O₁₅, belonging to tetragonal tungsten bronze materials, were grown by the slow cooling technique, and characterized by means of single crystal X‐ray diffraction: the structure was solved in the P4bm tetragonal space group, with the following unit cell parameters: a = 12.548(5), c = 4.042(5) Å, V = 636.4(9) ų. The three‐dimensional framework can be described as a layered structure down crystallographic axis c, with arrays of NbO₆ octahedra, whose corner sharing makes up the formation of tunnels filled up by Li, Pb and K displaying complex cation‐oxygen coordinations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of Nd:Sr3Ga2Ge4O14 crystals by a modified Bridgman method

Bridgman growth of Nd:SGG (Sr₃Ga₂Ge₄O₁₄) crystals has been investigated for the first time. Pt crucible of ∅︁25mm×250mm with a seed well of ∅︁10mm×80 mm is used, and seed is SGG crystal of ∅︁10mm×50mm grown by Bridgman method in advance. The growth parameters are optimized as the furnace temperature is set to 1450∼1500°C, temperature gradient in the crystal‐melt interface is less than 25 K/cm and growth rate is less than 0.5mm/h. The Nd:SGG crystals with 25mm in diameter and 60mm in length are grown successfully from 1.5 to 8at% Nd³⁺ doped stoichiometric Sr₃Ga₂Ge₄O₁₄ melt. The distribution coefficient and concentration of Nd³⁺ in Nd:SGG crystals are obviously higher than those of Nd:YAG crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of ZnO single crystals by an induced nucleation from a high temperature solution of the ZnO‐PbF2 system

To grow ZnO single crystals from a high temperature solution of the ZnO‐PbF₂ system, a gas cooling system was assembled at the bottom of the crucible to induce nucleation in the initial growth stage. The growth experiments were carried out in a homemade vertical Bridgman furnace and Pt crucible of 28 mm in diameter was used. The furnace temperature was set to 1100°C and the flow rate of the oxygen gas was optimized as 3.0 l/min. ZnO crystal up to 5∼8mm in the thickness was obtained with the lowering rate of 0.3 mm/h. XRD patterns showed that the as‐grown crystal was pure ZnO Wurtzite phase. The impurity ions were analyzed by the glow discharge mass spectroscopy (GDMS) as 390.0 ppm and 40.0 ppm for Pb²⁺ and F^‐, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature gradient controlled growth and optical properties of Er:BaY2F8 crystals

Single crystals of Erbium (Er) doped BaY₂F₈ have been obtained by the temperature gradient technique (TGT). No‐seed‐grown crystal of Er:BaY₂F₈, with the dimensions up to several centimeters, was obtained by self‐crystallization. The optimizations of various growth parameters were systemically investigated. The results indicated that the temperature gradient of 6‐7 K/mm and the cooling velocity less than 6 K/h were suitable for the crystal growth. The XRD data and the investigations on the growth striations by a stereo polarization microscope displayed that the [001] direction is the dominating direction for the crystal growth. The crystal grown by TGT often cracks along with the (100) plane, which is caused by the excessive decrease of the temperature during the crystal growth, for there is a rapid change in the thermal expansion curve of the BaY₂F₈ crystal in the temperature range from 800 °C to 900 °C. The spectral properties of Er:BaY₂F₈ single crystals have been studied and the effects of frequency up‐conversion of the crystals are reported. Spectral data suggest that the quality of Er:BaY₂F₈ crystal obtained by TGT method is good and the crystal has the potential application in laser devices. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure,growth and optical properties of Zn0.24Ni0.76(SO4)·7H2O single crystal

A new crystalline complex zinc nickel sulfate heptahydrate (ZNSH) has been prepared. The crystal structure was investigated by x‐ray single crystal diffraction method and the empirical formula is Zn_0.24Ni_0.76(SO₄)·7H₂O. The ZNSH crystal belongs to the orthorhombic space group P2₁2₁2₁ with cell parameters a = 6.7742(14) Å, b = 11.748(2) Å, c = 12.009(2) Å. The deep‐green ZNSH single crystal with dimension of 30 × 25 × 25 mm³ has been grown by the cooling solution method. The constituent ratio of ZNSH crystal grown from various compounding solutions at temperature range 40‐50 °C is approximate invariant. The crystal absorption spectra with theoretical analysis are reported. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ionic Conductivity of KTiOPO<Subscript>4</Subscript> Single Crystals Grown by Flux Crystallization under Different Conditions

The ionic conductivity of three KTiOPO₄ crystals grown from high-temperature solution–melts in combination with the Czochralski technique under different conditions has been investigated. The first crystal was obtained at a cooling rate V_g = 0.2–0.5 mm/day and a ratio of potassium and phosphorus concentrations in the solution–melt [K]/[P] = 2. The other two crystals were grown at a much higher velocity (V_g = 3–7 mm/day) from solution–melts with [K]/[P] = 1.5 and 1. It is shown that the crystal grown upon slow cooling at [K]/[P] = 2 has the lowest ionic conductivity: σ_||c = 1.0 × 10^–5 and 3 × 10^–11 S/cm at 573 and 293 K, respectively.     

Flux growth of straw‐like rutile monocrystals

Millimetric straw‐like rutile monocrystals were grown by the flux growth technique. A suitable mixture of flux (MoO₃, V₂O₅, Li₂CO₃) and amorphous TiO₂ gel was slowly cooled down to 750°C from 1250°C or 1350°C. The best yields of straw‐like rutile were obtained with a nutrient/flux ratio and a cooling rate in the range 0.015‐0.006 and 1.8‐1.9 K h^‐1, respectively. The hollowed crystals were characterized by powder and single‐crystal X‐ray diffraction, scanning electron microscopy, microthermometry, and µ‐Raman spectroscopy. As for skeletal crystal, the formation of axial canals in rutile is attributed to a lack of nutrient due to the viscosity of the melt and the high growth rate along [001]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal properties of a Nd:LuVO4 crystal

A Nd‐doped lutetium orthovanadate Nd:LuVO₄ crystal has been grown using a modified Czochralski method. The thermal properties of this crystal have been studied by measuring the thermal expansion, specific heat and thermal diffusivity. The thermal expansion coefficients are α₁₁ = 1.7 × 10^‐6, α₂₂ = 1.5 × 10^‐6 and α₃₃ = 9.1 × 10^‐6/K in the temperature range of 298–573 K along the three respective crystallographic axes. The specific heat is almost linear and increases from 0.442 to 0.498 Jg^‐1K^‐1 in the measured temperature range. The thermal diffusivity is anisotropic and decreases with increasing temperature from 295 to 548 K. At room temperature the calculated thermal conductivities κ₁₁ and κ₃₃ are 7.96 and 9.77 Wm^‐1K^‐1, respectively. These thermal parameters of Nd:LuVO₄ crystal have indicated that it is an excellent candidate laser material. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Flux growth and characterization of Ti‐ and Ni‐doped forsterite single crystals

Forsterite monocrystals doped with Ti and Ni were grown by the flux growth technique. A suitable mixture of flux (MoO₃, V₂O₅, Li₂CO₃) and nutrient was slowly cooled down to 750 °C from 1250 °C or 1350 °C. The crystals were then characterized by powder and single‐crystal X‐ray diffraction, scanning electron microscopy and differential scanning calorimetry (DSC). Variations observed in crystal size were attributed by both the varying experimental conditions in which they had been obtained, and to the amount of Ni substituted for Mg in the structure. High abundances of doped forsterite required a cooling rate of 1.8 K h^‐1. These synthetic, well‐characterized Ti and Ni doped forsterite crystals may have potential for exploitation in industrial fields. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth,structure and spectroscopic studies of a novel organic single crystal: L‐lysine p‐nitrophenolate monohydrate (LLNP)

A novel organic crystal, L‐lysine p‐nitrophenolate monohydrate (LLNP) has been grown successfully from an aqueous solution by the slow cooling method. Transparent single crystal of dimensions 22 × 12 × 12 mm³ has been obtained. The single crystal X‐ray diffraction has shown that LLNP belongs to the orthorhombic crystallographic system with space group P2₁2₁2₁. The functional groups and vibrational frequencies of the crystal have been identified using IR and Raman spectra. The proton and carbon configurations have been confirmed through ¹H‐NMR and ¹³C‐NMR spectra analyses. The UV‐Vis‐NIR transmittance spectrum for LLNP crystal has been recorded in the range from 200 to 2500 nm. The second harmonic generation (SHG) intensity of LLNP has been measured by powder SHG method and found to be as 4.2 times as that of KDP. The thermal properties have been studied by using thermo gravimetric (TG) and differential thermal analysis (DTA).     

Crystal structure,thermal and compositional deformations of β‐CsB5O8

The crystal structure of β‐CsB₅O₈ has been determined from X‐ray powder diffraction data using synchrotron radiation: Pbca, a = 7.8131(3) Å, b = 12.0652(4) Å, c = 14.9582(4) Å, Z = 8, ρ_calc = 2.967 g/cm³, R‐p = 0.076, R‐wp = 0.094. β‐CsB₅O₈ was found to be isostructural with β‐KB₅O₈ and β‐RbB₅O₈. The crystal structure consists of a double interlocking framework built up from B‐O pentaborate groups. The crystal structure exhibits a highly anisotropic thermal expansion: α_a = 53, α_b = 16, α_c = 14 · 10^‐6/K; the anisotropy may be caused by partial straightening of the screw chains of the pentaborate groups. The similarity of the thermal and compositional (Cs‐Rb‐K substitution) deformations of CsB₅O₈ is revealed: increasing the radius of the metal by 0.01 Å leads to the same deformations of the crystal structure as increasing the temperature by 35°C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An effective growth method to improve the homogeneity of relaxor ferroelectric single crystal Pb(In1/2Nb1/2)O3‐ Pb(Mg1/3Nb2/3)O3‐PbTiO3

Compositional segregation usually has negative effects on the growth of solid solution ferroelectric single crystals of Pb(In_1/2Nb_1/2)O₃‐Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ (abbr. PIN‐PMN‐PT or PIMNT). A modified Bridgman method was adopted in this work to control the segregation and improve the compositional homogeneity significantly. The characteristic of this work is to use multiround growths and gradient composition raw materials in order to keep the PbTiO₃ concentration constant during the crystal growth. As an example, the two‐round growth of ternary PIN‐PMN‐PT single crystal is conducted in the same Pt crucible with gradient raw materials, where the first‐round boule was used as the seed crystal for the second‐round growth. Our results show that the as‐grown (Ф80 mm × 270 mm) PIN‐PMN‐PT crystals exhibit higher phase transition temperatures (T_c∼180 °C, T_r/t∼110 °C) and larger coercive field (E_c∼5–5.5 kV/cm), which are much better than the performances of Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ crystals, and similar dielectric and piezoelectric performances (ε∼5000, tanδ∼1.25%, d₃₃∼1500 pC/N, k_t∼60%). And about 85 percent of the crystal boule grown by the two‐round growth technique could maintain its compositions around the morphotropic phase boundary.     

Domain structure and birefringence studies on a 0.91Pb(Zn1/3Nb2/3)O3 ‐0.09PbTiO3 single crystal

Domain structure and phase transition sequence of 0.91PZN‐0.09PT single crystal, grown from high temperature solution, have been analysed using polarised light microscopy. The domain structure of (001)_cub cut single crystal exhibit co‐existence of rhombohedral and tetragonal phases. The sequence and phase transition temperatures have been determined from temperature dependence of birefringence. Birefringence measurements during heating and cooling reveal a first order nature of phase transition between rhombohedral (R3m) and tetragonal (P4mm). The birefringence was measured with accuracy of 10^‐3. However, dielectric measurement does not provide any evidence of R3m ‐ P4mm phase transition. It is shown that in‐situ analysis of domain structure and phase transition can be used as non‐destructive analytical tool for determination of local composition and phase transition sequence. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Elliptic NdCrO3 microplate by a simple one‐step hydrothermal synthesis route and its characterization and magnetic properties

Elliptic NdCrO₃ microplates were synthesized by a simple and facile one‐step hydrothermal method of processing temperature 280 °C for 3 days. The products prepared in this paper have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), X‐ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR) and field‐emission scanning electron microscopy (FESEM). The magnetic properties of the final sample are also studied. The XRD pattern indicates the pure orthorhombic phase for NdCrO₃ particles, the XPS, XRF and FTIR results further demonstrate the composition and purity of the final product. A possible growth mechanism for elliptic NdCrO₃ microplates is proposed. Through the investigation of magnetic properties, it can be generally concluded that the orthorhombic elliptic NdCrO₃ microplates exhibit typical behaviors of magnetic transition, spin reorientation transition and magnetic exchange bias. The Néel temperature is 218 K and the spin reorientation transition temperature is 46 K. The hysteresis loop under 5 K shows that the value of exchange bias field (H_ex) is 12 Oe and the shift of remanent magnetization (ΔM) is 0.008 emu/g, respectively.     

Growth and crystal structure of the layered compound TlGaSe2

The semiconducting compound TlGaSe₂ was grown by solid state reaction technique. The crystal structure of this material was confirmed by single‐crystal X‐ray diffraction. TlGaSe₂ crystallizes in the monoclinic system with space group C2/c (No. 15), Z = 16 and unit cell parameters a = 10.779(2) Å, b = 10.776(1) Å, c = 15.663(5) Å, β = 99.993(6)°. The structural refinement converged to R(F) = 0.0719, R(F²) = 0.0652 and S = 1.17. The structure consists of a three‐dimensional arrangement of distorted TlSe₈ and GaSe₄ polyhedrons. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Luminescence of GaN single crystals prepared by heating a Ga melt in Na–N2 atmosphere

Colorless transparent prismatic crystals (0.5‐2.0 mm long) and hopper crystals (1.0‐2.5 mm long) of GaN were prepared by heating a Ga melt at 800°C in Na vapor under N₂ pressures of 7.0 MPa for 300 h. The photoluminescence (PL) spectrum of a prismatic crystal at 4 K showed the emission peaks of neutral donor‐bound exciton (D⁰‐X) and free exciton (X_A) at 3.472 eV and 3.478 eV, respectively, in the near band edge region. The full‐width at half‐maximum (FWHM) of (D⁰‐X) peak was 1.9 meV. The emission peaks of a donor–acceptor pair transition (D⁰‐A⁰) and its phonon replicas were observed in a lower energy range (2.9‐3.3 eV). The emission peaks of the D⁰‐A⁰ and phonon replicas were also observed in the cathodoluminescence (CL) spectrum at 20 K. The (D⁰‐X) PL peak of a hopper crystal at 4 K was at 3.474 eV (2.1 meV higher), having a FWHM of 6.1 meV which was over 3 times larger than that of the prismatic crystal. A strong broad band with a maximum intensity around 1.96 eV was observed for the hopper crystals in the CL spectrum at room temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and dielectric properties of Ta2O5 single crystal by the floating zone method

Large Ta₂O₅ single crystal with high‐dielectric permittivity was successfully grown by floating zone (FZ) method under air atmosphere. The grown crystal that has been obtained was typically about 8 mm in diameter and 90 mm in length. The crystal growth parameters were optimized. The crystal symmetry, characterized by means of X‐ray diffraction (XRD), was found to be tetragonal. The relative permittivity and loss tangent along growth and [001] direction were measured in the temperature range between ‐200 °C and 200 °C, which showed a strong dielectric anisotropy. At a frequency of 1 MHz and 20 °C, the dielectric permittivity along the growth direction and [001] direction are 81.17 and 25.04 respectively. The stabilization of high‐temperature phase can explain the dielectric enhancement.     

Fluorescence properties of Nd3+ doped stoichiometric LiNbO3 fiber single crystals by micro‐pulling down method

Using the micro‐pulling down (μ‐PD) method, 1 and 3 mol% Nd₂O₃ doped near stoichiometric lithium niobate (LiNbO₃) single crystal fibers were grown in 1 mm diameter and 35∼40 mm length. The grown crystal fibers were free of cracks and the homogeneous distribution of Nd³⁺ ion concentrations were confirmed by the electron probe micro analysis. The changes of fluorescence spectra were measured with respect to the Nd³⁺ ion doping concentration. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterisation of potassium cobalt nickel sulfate hexahydrate for UV light filters

A new single crystal for ultraviolet light filter, KCNSH (Potassium Cobalt Nickel Sulfate Hexahydrate) was designed and its crystal structure was studied using X‐ray diffraction in this paper. The empirical of the title compound is K₂Co_0.1Ni_0.9(SO₄)₂.6H₂O with formula weight 437.15. KCNSH crystal belongs to the monoclinic space group P2(1)/c, a=6.1390(3)Å, b=12.1839(6)Å, c=9.0095(4)Å, α=γ=90°, β=105.060(2)°, V=650.74(5)ų, Z=2, Dc=2.231g/cm³. Using the cooling solution method, we have grown a deep green KCNSH crystal with dimension of 12×12×40mm³. The transmission spectrum of KCNSH in the range from UV to near IR wavelengths, its thermal properties, and the relationship between the structure and optical transmission properties are also studied and further discussed in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)