Studies on the growth and defects of La3Ga5SiO14 (LGS) crystals

New and high quality piezoelectric crystals La₃Ga₅SiO₁₄ (LGS) grown by the Czochralski method in a Platinum or Iridium crucible are reported in this paper. The growth defects in the LGS crystals were investigated by Transmission electron microscopy (TEM). It was found that cracks, inclusions, grain boundary and thermal stress in the LGS crystals. Their formation mechanisms and the method of eliminating these defects are discussed. (© 2003 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)     

Influence of SiO32‐ impurity on growth habit of potassium dihydrogen phosphate crystal

By altering the concentration of silicate (SiO₃^2‐) impurity in the solution, a series of potassium dihydrogen phosphate (KDP) crystals was obtained by the conventional temperature cooling and the rapid growth methods, respectively. It was observed that the presence of SiO₃^2‐ made KDP crystals tapering in conventional cooling method, while more SiO₃^2‐ induced inclusions at prismatic sectors in the rapid growth method. Laser‐polarization‐interference results showed that SiO₃^2‐ extended the dead zone and reduced the growth rate of (100) face of KDP crystals. The negative influence of SiO₃^2‐on the growth was considered absolutely similar to the effect of cations. It was also suggested that the stability of solution doped with SiO₃^2‐ was improved without seed crystals, while it was destructed with seed crystals. The inhibition mechanism was analyzed in terms of SiO₃^2‐ absorption on (100) face. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

硅酸镥闪烁晶体的生长与缺陷研究

本文采用提拉法生长出了硅酸镥闪烁晶体,讨论了晶体生长中遇到的问题,所生长的硅酸镥晶体有开裂、解理、多晶、回熔现象等宏观生长缺陷和包裹物、位错等微观缺陷.开裂是由热应力和晶体解理两种因素引起的,其中热应力是导致开裂的主要因素,优化生长工艺条件可完全避免开裂.晶体中存在两种包裹物,成份分别为氧化镥和坩埚材料铱,氧化镥很可能是未参加反应的原料,也有可能是氧化硅挥发而导致氧化镥析出.     

The growth and spectral analysis of mixed crystal of Yb‐doped Lu0.5Y0.5PO4 mixed crystals

A new kind of 5 at% Yb‐doped Lu_0.5Y_0.5PO₄ crystals were firstly grown by spontaneously nucleated high‐temperature solution method using lead pyrophosphate (Pb₂P₂O₇) as the solvent. The X‐ray powder diffraction (XRPD) patterns recorded at room temperature showed the crystals possessed tetragonal xenotime structure. The polarized absorption spectra and the fluorescence spectra of Yb:Lu_xY_1‐xPO₄ were measured at room temperature, respectively. The results show that Yb:Lu_xY_1‐xPO₄ mixed crystal will be a promising laser material if the crystal size and quality is further improved.     

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)     

Effect of axial vibration on Bi12SiO20 crystal growth by vertical Bridgman technique

Bi₁₂SiO₂₀ single crystals have been grown successfully by vertical Bridgman technique. During the crystal growth process, different axial vibration amplitudes of 50 μm, 70 μm and 100 μm were applied with the same vibration frequency of 50 Hz. The effect of different axial vibration amplitudes on quality of the as‐grown Bi₁₂SiO₂₀ single crystals was discussed. The crystals have been characterized by X‐ray rocking curve optical and absorption spectrum. The experimental results reveal that the axial vibration amplitude has a pronounced effect on quality of the as‐grown Bi₁₂SiO₂₀ single crystals. (© 2009 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)     

SiC crystal growth from transition metal silicide fluxes

SiC crystal growth in transition metal silicide melts was investigated by using spontaneous infiltration and solution methods. In the infiltration experiments, SiC powder preforms were infiltrated with Fe_xSi_y (Fe₃Si, Fe₅Si₃ and FeSi) and CoSi melts. The dissolution and precipitation of SiC led to SiC crystals growth in the infiltrated Fe₅Si₃ and CoSi melts, SiC particles coalescing in FeSi and free carbon precipitation in Fe₃Si. In the solution experiments, carbon from the graphite crucible dissolved in and reacted with FeSi₂ and Ti_2.3Si_7.7 to form SiC crystals. Scanning electron microscopy (SEM), X‐ray diffraction (XRD) and Raman scattering spectrometer were employed to investigate SiC crystals growth. Based on the investigation, the effect of solution content on the SiC crystal growth, the growth mechanisms in both methods and prototypes of the SiC crystals are also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bridgman and Czochralski growth of Ge?Si alloy crystals

Ge_1–xSi_x crystals were grown with the Bridgman and the Czochralski method over a wide concentration range. With the Bridgman process single crystals up to 40 at.% Si were possible. The reasons for polycrystalline growth were the permanent contact of the interface with the crucible wall in combination with curvature towards the crystal and inclusions of high Si concentration. Analysis of striations in Czochralski grown material showed that in this process the crystal does not continuously grow in one direction but consists of piece-wise grown crystals in which the composition permanently changes. According to that fact the main reason for polycrystalline growth in the Czochralski process is common due to lattice mismatch between the seed and equilibrium concentration transients in the crystal corresponding to the microscopic growth rates.     

Investigations on the crystallization of larger NaA and NaX zeolite crystals in the presence of triethanolamine (I). The influence of Na2O and SiO2 content

Sodium silicate-aluminate aqueous systems with various contents of Na₂O and SiO₂ containing triethanolamine were crystallized. Optimum Na₂O and SiO₂ contents have been observed to give NaA and NaX zeolite crystals with dimensions up to 80 μm. For NaA crystals the values are: ∼ 3.5 mass% Na₂O, ∼ 1.65 mass% SiO₂; for NaX crystals ∼ 2.5 mass% Na₂O, ∼ 1.5 mass% SiO₂. – The effect of other additives on crystal size is proved. – The results are discussed in terms of nucleation and growth, reaction rate, and supersaturation. Supposition are made to gain larger crystals by maintaining the excess of solute over a longer period of time.     

Growth behaviour of bulk GaN single crystals grown with various flux ratios using solvent‐thermal method

Bulk GaN single crystals were grown using a solvent‐thermal method. They were grown for 200 h at 600 °C and 800 °C using 8 MPa of N₂ gas and 1–3 mm sized pyramid GaN single crystals. Pure Na, NaN₃ and Ca were used as the flux. The mole fraction of the [flux]/([flux] + [Ga]) was 0.30–0.67. The growth behavior differed according to the flux ratio. The quality of the bulk GaN single crystals was improved by increasing the flux ratio. The bulk GaN single crystals formed by spontaneous nucleation were deposited on the BN crucible wall and bottom during the first step of synthesis. The wurtzite structure of the GaN grown single crystal was confirmed by x‐ray diffration. The chemical composition was analyzed by electron probe microanalysis. The quality and optical properties of the GaN single crystal were examined by Raman spectroscopy and photoluminesence analysis. (© 2005 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.     

Evaporation induced diameter control in fiber crystal growth by micro‐pulling‐down technique: Bi4Ge3O12

Diameter self‐control was established in Bi₄Ge₃O₁₂ fiber crystal growth by micro‐pulling‐down technique. In accordance with Bi₂O₃‐GeO₂ phase diagram, the diameter was controlled due to compensation of solidification with evaporation of volatile Bi₂O₃ self‐flux charged into the crucible with excess. The crucibles had capillary channels of 310 or 650 μm in outer diameter. The crystals up to 400 mm long and 50‐300 μm in diameter were grown at pulling‐down rates of 0.04‐1.00 mm/min. The melt composition and the pulling rate were generally only two parameters determining solidification rate. As a result, crystals with uniform (± 10%) diameter and aspect ratio up to 10⁴ were produced without automation of the process. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation on growth defects in Pb(Zn1/3Nb2/3)O3‐PbTiO3 crystals

Relaxor ferroelectric crystal (1‐x)Pb(Zn_1/3Nb_2/3)O₃‐xPbTiO₃ (PZNT) with x=0.07 (PZNT93/7) has been grown by the vertical Bridgman method from the high temperature solution of PZNT‐PbO system. The growth defects, such as nucleation core, inclusions, boundaries and particles, were investigated by optical microscope and scanning electron microscope. Sub‐structures were found in the flux inclusions and the lack of ZnO component in PZNT crystals was attributed to the existence of ZnO particles in the inclusions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of γ‐irradiation on spectral properties of undoped Y2SiO5 crystals

The absorption spectra of undoped Y₂SiO₅ crystals were studied before and after γ‐irradiation. After γ‐irradiation, the additional absorption peaks at 260‐270 and 320nm were observed in as‐grown and H₂‐annealed Y₂SiO₅ crystal, but it did not occur in air‐annealed Y₂SiO₅ crystal. These absorption peaks were attributed to F color centers and O^– hole centers, respectively. Owing to more oxygen vacancies and color centers in H₂‐annealed Y₂SiO₅ crystal than that in as‐grown Y₂SiO₅ crystal after γ‐irradiation, the additional absorption peaks were more intense in the former than that in the latter. With the irradiation dose increasing from 20 to 220kGy, the intensity of additional absorption peaks increased. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Numerical simulation of thermal and mass transport during Czochralski crystal growth of sapphire

The thermal and flow transport in an inductively heated Czochralski crystal growth furnace during a crystal growth process is investigated numerically. The temperature and flow fields inside the furnace, coupled with the heat generation in the iridium crucible induced by the electromagnetic field generated by the RF coil, are computed. The results indicate that for an RF coil fixed in position during the growth process, although the maximum value of the magnetic, temperature and velocity fields decrease, the convexity of the crystal‐melt interface increases for longer crystal growth lengths. The convexity of the crystal‐melt interface and the power consumption can be reduced by adjusting the relative position between the crucible and the induction coil during growth. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bridgman growth of langasite‐type piezoelectric crystals

Three langasite family crystals of Sr₃Ga₂Ge₄O₁₄ (SGG), Ca₃NbGa₃Si₂O₁₄ (CNGS), and Sr₃NbGa₃Si₂O₁₄ (SNGS) were successfully grown by the modified Bridgman method. Among them, SGG crystals up to 2 inches were obtained with the multi‐crucible industrial Bridgman furnace; SNGS crystal grown in any orientation direction other than along a‐axis was realized. Commercially availability SGG boules and the advantage in SNGS crystal indicated that the modified Bridgman technique is a prospective method to realize the mass‐production of the langasite‐type crystals. (© 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)     

Domain structures and etching morphologies of lithium niobate crystals with different Li contents grown by TSSG and double crucible Czochralski method

Stoichiometric lithium niobate single crystals with different Li contents have been grown both by the top‐seeded solution growth (TSSG) method from potassium containing flux and by the double crucible Czochralski (DC Cz) method. Spectroscopic properties (e.g. the UV absorption edge, Raman linewidth) and the Curie temperature measurement have been used for the characterization of the crystal composition. The double crucible Czochralski method is found to be suitable for mass production of stoichiometric LiNbO₃ with Li content larger than 49.7 mol% and homogeneity of 0.03 mol%. The domain structures and etching morphologies on negative and positive c‐surface were also investigated by chemical etching method. A new domain structure of three‐fold symmetric sectors were observed in near‐stoichiometric LiNbO₃ grown by TSSG method. The straight line arrangement hillocks on negative c‐surface and the net‐like arrangement etch lines were observed and explained by stress etching mechanism. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)