Enantiomorphism of the Ca3Ga2Ge4O14 compound and comparison of the Ca3Ga2Ge4O14 and Sr3Ga2Ge4O14 structures

The absolute crystal structures of two enantiomorphic forms of the Ca₃Ga₂Ge₄O₁₄ crystals (a = 8.075(1) ?, c = 4.9723(6) ?, space group P321) with the positive and negative senses of the optical activity are determined using X-ray diffraction analysis. The final R factors are as follows: R = 1.75% and R _w = 2.57% for the crystal with the positive sense of the optical activity and R = 1.86% and R _w = 2.78% for the crystal with the negative sense of the optical activity. The replacement of the Ca²⁺ ions by larger Sr²⁺ ions (with the formation of the Sr₃Ga₂Ge₄O₁₄ compound) leads to an anisotropic expansion of the crystal lattice (with a more considerable increase in the lattice parameter a as compared to the lattice parameter c), a change in the occupation of the 1a and 3f positions by the Ga³⁺ and Ge⁴⁺ ions, and symmetrization of the octahedra and tetrahedra forming the structural framework. The shape of the dodecahedron changes so that its size along the polar electric axis 2 increases significantly. This change is the main factor responsible for the increase in the piezoelectric activity of the Sr₃Ga₂Ge₄O₁₄ compound as compared to the piezoelectric activity of the Ca₃Ga₂Ge₄O₁₄ compound. Original Russian Text ? B.V. Mill, A.A. Klimenkova, B.A. Maximov, V.N. Molchanov, D.Yu. Pushcharovsky, 2007, published in Kristallografiya, 2007, Vol. 52, No. 5, pp. 816–823.     

The crystallization of vitreous and metastable Pb5Ge3O11

Vitreous Pb₅Ge₃O₁₁ was prepared by water quenching and by roller quenching. The crystallization was studied by DTA, X-ray diffraction, and TEM. After a glass transition at 325°C, meta-stable Pb₅Ge₃O₁₁ crystallized exothermically at 370°C. This was subsequently followed by the formation of the stable phase of the same composition, again exothermically at 490°C.     

Floating-zone growth of large high-quality CoAl2O4 single crystals

We report the first successful floating-zone growth of high-quality CoAl₂O₄ single crystals with volume up to 1 cm³ free from inclusions and sub-grains. The neutron rocking curves of the CoAl₂O₄ crystal have the width of about 0.30 degree proving the excellent quality of the grown samples. X-ray synchrotron experiments show that crystals have spinel structure with the lattice constant a₀=8.09853(1) Å. Magnetization measurements give the effective magnetic moment μ_eff=4.63 μ_B per Co⁺² ion in a good agreement with previous measurements on ceramic samples.     

Flux growth of PbMg1/3Ta2/3O3 single crystals

Single crystals of PbMg_1/3Ta_2/3O₃ (PMT) were grown by the flux method. The PbO–Pb₃O₄–B₂O₃ system was used as a solvent. Transparent and light yellow PMT single crystals of rectangular shape and dimensions up to 10×6×4 mm³ were obtained. For the applied growth conditions only, the crystals of the perovskite structure were grown. X-ray diffraction tests showed that at room temperature PMT exhibits cubic symmetry with lattice parameter a=4.042(1) Å. Dielectric studies pointed to relaxor properties of PMT. The characteristic broad and frequency-dependent maximum of dielectric permittivity was observed at 179.7 K (1 kHz).     

Growth of BPO4 single crystals from Li2Mo3O10 flux

Transparent single crystal of BPO₄ with a typical sizes of 5 × 7 × 9 mm³ have been grown by the top-seeded solution growth (TSSG) slow-cooling method using Li₂Mo₃O₁₀ as the flux. X-ray powder diffraction result shows that the as-grown crystal was well crystallized and indexed in a tetragonal system. The processing parameters and the effects of the flux on the crystal growth were investigated.     

Y2O3-Al2O3-Nd2O3 phase diagram and the growth of (Y,Nd)3 Al5O12 single crystals

The optimum compositions of the melts used for the growth of yttrium-aluminum garnet (YAG) single crystals with different neodymium contents are determined using the phase diagram of the ternary system Y₂O₃-Al₂O₃-Nd₂O₃ with the binary sections Y₃Al₅O₁₂-Nd₂O₃ and Y₃Al₅O₁₂-Nd₃Al₅O₁₂. A number of melt compositions characterized by one garnet phase, namely, (Y,Nd)₃Al₅O₁₂, are established. Single crystals of yttrium-aluminum garnets with a high content of the activator (up to 2.6 wt % Nd) are grown by the Czochralski method. __________ Translated from Kristallografiya, Vol. 48, No. 5, 2003, pp. 945–949. Original Russian Text Copyright ? 2003 by Soboleva, Chirkin. Dedicated to the 60th Anniversary of the Shubnikov Institute of Crystallography of the Russian Academy of Sciences     

Refinement of the crystal structures of the La3Ta0.5Ga5.5O14 and La3Nb0.5Ga5.5O14 compounds

This paper reports on the results of accurate X-ray structural investigations of single crystals La₃Ta_0.5Ga_5.5O₁₄ (a = 8.2260(1) ?, c = 5.1207(1) ?, R/R _w = 1.09%/1.10%, 3868 unique reflections) and La₃Nb_0.5Ga_5.5O₁₄ (a = 8.2237(1) ?, c = 5.1247(1) ?, R/R _w = 1.02%/1.03%, 3735 unique reflections) (space group P321, Z = 1, sinϑ/λ|_max ≈ 1.34 ?⁻¹ for both compounds). Using sets of data with a large number of high-angle reflections makes it possible to reliably compare the crystal structures by applying statistical tests. The structural differences between the La₃Ta_0.5Ga_5.5O₁₄ and La₃Nb_0.5Ga_5.5O₁₄ crystals are weakly pronounced, which correlates with the closeness of their piezoelectric characteristics. Original Russian Text ? A.P. Dudka, B.V. Mill, Yu.V. Pisarevsky, 2009, published in Kristallografiya, 2009, Vol. 54, No. 4, pp. 599–607.     

Ambient-condition growth of superconducting YBa2Cu4O8 single crystals using KOH flux

YBa₂Cu₄O₈ is a stoichiometric oxide superconductor of T_c80 K. Unlike YBa₂Cu₃O_7−δ, this compound is free from oxygen vacancy or twin formation and does not have any microscopic disorder in the crystal. Doping with Ca raises its T_c to 90 K. The compound is a promising superconductor for technological application. Up to now, single crystals have not been grown without using specialized apparatus with extremely high oxygen pressure up to 3000 bar and at over 1100 °C due to the limited range of reaction kinetics of the compound. This fact has delayed the progress in the study of its physical properties and potential applications. We present here a simple growth method using KOH as flux that acts effectively for obtaining high-quality single crystals in air/oxygen at the temperature as low as 550 °C. As-grown crystals can readily be separated from the flux and exhibit a perfect orthorhombic morphology with sizes up to 0.7×0.4×0.2 mm³. Our results are reproducible and suggest that the crystals can be grown using a conventional flux method under ambient condition.     

Large-size β-Ga2O3 single crystals and wafers

Large-size single crystals of β-Ga₂O₃ with 1 inc in diameter have been grown by the floating zone technique. The stable growth conditions have been determined by the examination of the crystal structure. Wafers have been cut and fine polished in the (1 0 0), (0 1 0) and (0 0 1) planes. These were highly transparent in the visible and near UV, as well as electrically conductive, indicating the potential use of β-Ga₂O₃ as a substrate for optoelectic devices operating in the visible/near UV and with vertical current flow.     

Phase equilibria and growth of β-BaB2O4 crystals in the BaB2O4-Ba2Na3[B3O6]2F system

A complex investigation of the BaB₂O₄-Ba₂Na₃[B₃O₆]₂F cut, which belongs to the ternary mutual Ba, Na//BO₂, F (BaB₂O₄-(NaBO₂)₂-(NaF)₂-BaF2) system, has been performed. The cut is quasibinary, with the following eutectics coordinates: 810 ± 5°C, 85 mol % Ba₂Na₃[B₃O₆]₂F, 15 mol % BaB₂O₄. It is shown that this system can be used to grow bulk β-BaB₂O₄ crystals.     

Czochralski grown Ga2O3 crystals

We report on the successful growth of β-Ga₂O₃ single crystals using the Czochralski method. Model calculations show that the gas phase consists of Ga₂O, GaO or Ga independent of the ratio of oxygen and Ar or N₂. We find that for growing single crystals the evaporation has to be suppressed by a finite amount of oxygen. A CO₂/Ar gas atmosphere was found to meet this requirement.     

Growth and properties of layered oxycarbonate Bi2Sr4Cu2CO3O8 single crystals

Layered oxycarbonate Bi₂Sr₄Cu₂CO₃O₈ single crystals have been obtained for the first time by free growth in closed vapor-phase cavities. The morphology, structure, composition, and superconducting properties of these crystals have been investigated.     

Improved growth of PbI2 single crystals

The phase equilibrium and the crystallization process of lead iodide (PbI₂) melt have been primarily investigated according to the lead–iodine phase diagram. It is found that the iodine evaporation and the segregated lead deposition are the two important factors that affect the PbI₂ crystal quality. The new method of Pulling U-type quartz growth ampoule has been made to impede the decomposition of PbI₂ and the vaporization and condensation of iodine. An orange and translucent PbI₂ single crystal of large size was obtained by the improved growth method, i.e. U-type ampoule pulling. Resistivity of the as-grown crystal is up to 4×10¹¹ Ω cm, and IR transmission is up to 45% in the region from 7800 to 450 cm⁻¹. Therefore, the improved growth method is a promising convenient new method for the growth of high quality PbI₂ crystals.     

Growth of pure and RE-doped Y2O3 single crystals by LHPG technique

High-quality and crack-free Y₂O₃ single crystals containing low concentrations of Tm³⁺, Tb³⁺ and Yb³⁺ were obtained. The crystals were grown in the form of monocrystalline fibers by using a floating zone method with laser heating (laser-heated pedestal growth).     

Growth of Tb3Ga5O12 fiber and bulk crystals using micro-pulling-down apparatus

A micro-pulling-down process, using Ir crucibles and RF heating, has been used to grow single-crystal fiber and bulk crystals of Tb₃Ga₅O₁₂ garnet (TGG). Single crystals ranging up to 450 mm in length have been produced. The crystals were 1–4 mm in diameter and were seeded-grown in the direction close to 1 1 1. The maximal crystal diameter achieved was 10 mm. Dependence of behavior of the solid–liquid interface on the growth parameters (temperature and pulling-rate) is discussed in detail.     

Study on phase diagram of Bi2O3---SiO2 system for Bridgman growth of Bi4Si3O12 single crystal

Phase relation of Bi₂O₃---SiO₂ system was evaluated experimentally from DTA and XRD measurements and its stable and metastable phase diagrams were proposed. Although BSO melts near-congruently at 1025°C in the stable phase equilibrium, its melt crystallizes to form metastable phase Bi₂SiO₅ in accordance with the metastable phase diagram while cooling. Therefore, BSO couldn't nucleate and crystallize spontaneously without crystal seed and only Bi₂SiO₅ crystallized at about 850°C with significant supercooling during Bridgman growth. BSO single crystal with 20×20×100mm³ was grown in a vertical Bridgman furnace with a BSO seed according to its phase diagram. The measuring results of scintillation properties of BSO specimen show that its decay constant is 91 ns (about 1/3 of BGO) and light output is 23% of BGO.     

Flux growth and characterizations of NdPO4 single crystals

Neodymium phosphate single crystals, NdPO₄, have been grown by a flux growth method using Li₂CO₃-2MoO₃ as a flux. The as-grown crystals were characterized by X-ray powder diffraction(XRPD), differential thermal analysis (DTA) and thermogravimetric analysis (TG) techniques. The results show that the as-grown crystals were well crystallized. The crystal was stable over the temperature range from 26 to 1200 °C in N₂. The specific heat of NdPO₄ crystal at room temperature was 0.41 J/g °C. The absorption and the fluorescence spectra of NdPO₄ crystal were also measured at room temperature.     

Bi4Si3O12-Bi4Ge3O12赝二元系统析晶行为及其晶体生长

本文采用固相合成方法制备了Bi4(GexSi1-x)3O12(BGSO)固溶体(x=0～0.4),研究了它的固溶特性和析晶行为。实验结果表明,不同组成混合料在900℃左右固相反应能生成BGSO纯相;XRD分析显示,在x=0～0.4区间内,Bi4Si3O12和Bi4Ge3O12可以完全互溶,其晶格常数随x的增加呈线性增长。采用坩埚下降法生长了x=0.15组成的BGSO混晶,获得了透明晶体,并测试了晶体的光学性能。     

Elastic constants and structure of the vitreous system Co3O4P2O5

The elastic moduli of the entire vitreous range of the system CoPO that can be prepared by melting together Co₃O₄ and P₂O₅ oxides in open crucibles, have been measured by ultrasonic techniques at 15 MHz. The bulk, shear, longitudinal and Young's moduli and the Poisson ratio are found to be rather sensitive to the glass composition. It is found from this ultrasonic data, that the glass system can be divided into “three compositional regions”. This behaviour is qualitatively interpreted in terms of the cobalt co-ordination, crosslink densities, interatomic force constants and atomic ring sizes. Also presented is a full discussion of effects of annealing on elastic properties.     

Crystal growth of NdAl3(BO3)4 from K2O/MoO3/Nd2O3/B2O3/KF flux

NdAl₃(BO₃)₄ single crystals were grown by the flux method and the TSSG technique using a K₂O/3MoO₃/B₂O₃/0.5Nd₂O₃/KF flux system. Light-violet clear crystals could be obtained. The effects of fluoride on the growth of NAB crystals were investigated. As the content of KF was gradually increased, the growth form of NAB was changed from the equant to the columnar and the primary crystalline region of NAB was shrinked. At the ratio of KF/K₂O = 0.75, NAB crystals could not be grown.