Enhancement of the Automatic Diameter Control System for the Czochralski Growth of Nd:GdVO4 Crystals

The automatic diameter control system was enhanced for the growth of Nd-doped GdVO₄ single crystals by the Czochralski method. It was estimated that excessive amount of feedback in the control system is the effective way to improve the shape of rare-earth vanadate single crystals. The spectral analysis for crystal weight and generator power signals was carried out in real time during growth process for determination of oscillations in the control system.     

Growth Rate anisotropy of the K2(S,Cr)O4 Mixed Crystals Grown from Aqueous Solution

The ratio of growth rates of the K₂(S,Cr)O₄ crystals in the [100] and [001] directions (the anisometry coefficient) is proportional to the initial effective supersaturation of the solutions from which the crystals were grown. The values of the factors of asymmetry and excess of distribution of the crystal anisometry coefficient are affected by the composition of solution. The change in the values of these factors is caused by the change in the value of the initial supersaturation of solution according to the specific features of the solubility diagram.     

The edge-defined film-fed growth of controlled shape crystals

The growth of shaped crystals is examined in the various meniscus-controlled growth processes such as Czochralski, floating zone, Stepanov, and edge-defined film-fed growth (EFG). The basic physical processes which shape the crystal are the same in these techniques; they involve the interaction of the three interfaces at the crystal–liquid–vapor junction. Specifically, for a crystal of constant dimensions, the angle ø between the meniscus and the growth axis must be ø_o (a constant; for silicon, ø_o 11°). The degree of crystal shape control and the range of cross-sectional shapes which can be grown in a stable manner by the different techniques are shown to depend on the details of the meniscus shape and of the heat flow in the systems. The use of a die shaper which constrains the meniscus distinguishes the EFG and Stepnov processes from the other methods. The use of a wetted die in EFG versus a non-wetted die in Stepnov growth is shown to have an additional effect on the ability to control the crystal shape and dimensions. The role of the die shaper is examined in detail from the points of view of die material selection (e.g., wettability and chemical compatibility) and die design. The advantages and disadvantages of using wetted and non-wetted dies in the shaping process are discussed from both the theoretical and practical points of view. Specific numerical examples in the paper deal with the growth of silicon ribbons.     

Crystal growth and dislocation arrangement of Czochralski alexandrite (BeAl2O4:Cr) single crystals

The [001] oriented alexandrite (BeAl₂O₄:Cr) single crystals have been grown by the Czochralski pulling technique. The X-ray topographic investigation indicates that the grown-in dislocations mainly originate from the seed and propagate along the path normal or nearly perpendicular to the growth interface. The dislocation density and arrangement is closely related to the quality of the seed crystal.     

Optical properties of KGd(WO4)2 single crystals studied by Brillouin spectroscopy

The results of a study of KGd(WO₄)₂ single crystals by Brillouin scattering method are presented. The Brillouin spectra for the acoustic phonons propagating in the [100], [010], [001], [110] and [101] directions, taken in 90° and 180° scattering geometry at room temperature have been recorded. Using the Brillouin spectroscopy the refractive indices for some directions of KGd(WO₄)₂ crystals were determined. The refractive indices were also calculated for the same directions by the rotation transformation of the principal optical axes of the optical indicatrix to the crystallographic directions of KGd(WO₄)₂ crystals. Moreover, some anomalies of the acoustic phonons propagating connected with birefringence of KGd(WO₄)₂ crystals were discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of dysprosium garnet single crystals with spiral shape using Czochralski technique

The growth conditions of dysprosium garnets single crystals, to obtain a long and good spiral shape crystal, have been investigated using the conventional Czochralski technique along the [111] pulling direction. The good spiral shape of Dy₃Ga₅O₁₂ single crystal with 40 mm in length is grown with its spiral pitch and spiral diameter of 20 mm and 15 mm, respectively.     

Elastic properties of KGd(WO4)2:Ho3+ single crystals studied by Brillouin spectroscopy

The analysis some of the acoustic phonons propagating in pure and Ho³⁺‐doped KGd(WO₄)₂ single crystals in the GHz frequency range by Brillouin scattering method has been presented. For investigated crystals the velocities of the longitudinal and transverse acoustic phonons [100], [010], [001], [101], [101] and [110] have been determined. Moreover, the value of elastic constants C₂₂, C₄₄ and C₆₆ of pure and Ho³⁺‐doped KGd(WO₄)₂ single crystals have been estimated. It was revealed that the presence of the Ho³⁺‐ions in KGd(WO₄)₂ crystals, for the used doping concentration 1 at% and 8 at%, does not influence their elastic properties. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Nature of One-sided Intergrowths on (001) of Triclinic Centrosymmetric K2Cr2O7 (II)

SHUBNIKOV first observed in 1912 that centrosymmetric K₂Cr₂O₇ crystals (P1 ) exhibit a growth anomaly in highly supersaturated solutions. The (001) faces of these crystals are always smooth, the parallel opposite faces are always rough. Electron micrographs show these rough surfaces to be crystallites that have grown in stacks. In Part I of this publication, the crystallite orientation was determined using electron-induced diffraction methods. As a rule, these crystallites are parallel intergrowths. Only a small number of crystals near the surface of the host crystal are twinned according to [010]. Part II sought to ascertain the cause of these one-sided intergrowths. To determine the most favourable energetic arrangement of two intergrown individuals, interactions across the intergrowth face as a function of shifts parallel to (001) and to (001 ) were calculated, 64 theoretically possible cases were considered. Only in the [010]-twin and the seldom-occurring [11 0]-twin is an approximation of the 2/m symmetry of the macroscopic twin arrangements also found in the intergrowth structure, and this is the case only when the (001 ) faces of the host and guest crystal are intergrown.     

Long-term Crystal Growth under Microgravity during the EURECA-1 Mission (I) THM Growth of AlxGa1−xSb

Long-term crystal growth experiments were successfully performed under microgravity conditions during the first flight of the unmanned mission EURECA-1 in the automatic mirror furnace (AMF). Two crystals of Al_xGa_1−xSb with [001] and [111] orientation respectively were grown from gallium solution by the travelling heater method. The grown length of the single crystals is 4.0 mm and 4.2 mm respectively. The space-grown samples show a high microscopic homogeneity which indicates the absence of time dependent convection. From pulse markers a constant growth rate of 0.6 ± 0.1 μm/min is measured which is lower than 0.8 ± 0.1 μm/min obtained in earth grown reference samples. Details about the experiment performance and the growth results are given.     

Growth of Nd:GdVO4 Single Crystal and its Laser Output at 1062 nm,1342 nm

A new liquid‐phase method synthesizing Nd:GdVO₄ polycrystalline materials was introduced. High optical quality Nd:GdVO₄ single crystals have been successfully grown by the Czochralski method. The effective segregation coefficients of Nd ion in Nd:GdVO₄ crystal have been measured and discussed. Laser outputs at 1.06 μm and at 1.34 μm were achieved when Nd:GdVO₄ crystal samples of 0.52 at% Nd concentration were pumped by a high‐power LD. A maximum output of 14.5 W at 1.06 μm has been obtained when the pump power is to 26 W, giving the slope efficiency of 63%. It is reported the first time that up to 4.64 W power laser at 1.34 μm has been achieved with optical conversion efficiency of 31.4% and slope efficiency of 32.9%.     

Contribution to the study of elastic properties of KGd(WO4)2:Er3+ single crystals by Brillouin spectroscopy

In this paper we present the study of the acoustic phonons propagating in Er³⁺‐doped KGd(WO₄)₂ single crystals by Brillouin spectroscopy. For the investigated crystals the velocities of the longitudinal and transverse acoustic phonons [100], [010], [001], [101] and [110] have been determined. Moreover, the values of the elastic constants: C₂₂, C₄₄ and C₆₆ of Er³⁺‐doped KGd(WO₄)₂ single crystals have been estimated. It was revealed that the presence of the Er³⁺‐ions in KGd(WO₄)₂ crystals, for the used doping concentration 1 at% does not influence their elastic properties. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigations on the Growth and Laser Properties of Nd:GdVO4 Single Crystal

In this paper, we report the growth of laser crystal Nd:GdVO₄ by the Czochralski method, and discuss the morphology of the crystal. The polarization absorption and emission spectra of Nd:GdVO₄ were measured. The lifetime of the Nd:GdVO₄ at 1064 nm is 100μs. An output power up to 1 W at 1064 nm has been achieved with a 3 mm × 3 mm × 1 mm crystal sample when pumped by a 1.9 W cw laser diode.     

Thermal conductivity and refractive indices of Nd:GdVO4 crystals

The thermal conductivities of Nd:YAG, M(Y,Gd)VO₄ crystals were measured at 298 K. The value of Nd:GdVO₄ crystal along <001> direction was 11.4 W/mK, which was higher than that of YAG crystal measured to be 10.7 W/mK. The principal refractive indices of Nd:GdVO₄ crystal in the temperature range from 20 °C to 170 °C were determined by auto‐collimation method. Based on the measured values of refractive indices, the Sellmeier equation and expression of temperature dependence of refractive indices have been obtained. The measured results show that the birefringence Δn is 0.22007 at 20 °C and temperature coefficient of birefringence is 4.33 × 10⁻⁶/°C for 1.064 μm. These results prove that the GdVO₄ crystal is a laser crystal with excellent thermal and birefringence properties. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology of β-BaB2O4 (BBO) Crystals in Relation to its Structure and Growth Conditions

β-BaB₂O₄ (BBO) crystals with well-defined morphology have been grown from Na₂O solutions using the top seeded solution growth (TSSG) method. The crystal morphology in relation to its structure and growth conditions has been studied in detail on the basis of crystallography and crystal chemistry. It is found that the morphological characteristics are related to the orientations of structural unit (B₃O₆)^3— anion rings in the crystal. On the other hand, the growth parameters may greatly affect the appearance of faces of the crystal, but the crystals still generally take trigonal in outline and have a diagnostic character of point group 3m. The observed morphology is in disagreement with BFDH and PBC analyses and is explained from the incorporation of the growth units on the faces and facets. Since the incorporation rates of the growth units are different on different faces, the boule habits with well-defined morphology are formed.     

Nd:YVO4 crystal growth by Czochralski technique with a submerged plate

This paper is to investigate the growth of Nd:YVO₄ (yttrium vanadate) crystal by the modified Czochralski technique with a submerged plate. Numerical studies are performed to examine melt convection and heat transfer during Nd:YVO₄ growth. The attention is paid to study the effects of initial elevation of the submerged plate, crystal diameter, and melt level on melt inclusions. It is found that the increase in crystal rotation rate and crystal diameter, and the decrease in melt level will increase the axial temperature gradient at the edge and in the center of the crystal, and change the interface shape from convex to flat. The experiments are also carried out to confirm the feasibility of the proposed new technique for controlling melt inclusions in Nd:YVO₄ crystal growth.     

Crystal Growth in Magnetic Fields (I) Crystallization of Me (NH4)2(SO4)2 · 6 H2O (Me = Zn,Cu, Ni,Fe) from Aqueous Solutions in Moderate Magnetic Fields

There are several reports in the literature concerning the study of the influence of magnetic fields on nucleation and crystal growth. Because of the partially opposite findings, the question whether the application of magnetic fields especially for mass crystallization processes may be of advantage has not been cleared yet. Therefore, the displacement rates of [110] and [001] single crystal faces of four Tutton's salts Me(NH₄)₂(SO₄)₂ · 6 H₂O (Me = Zn, Cu, Ni, Fe) from supersaturated aqueous solutions in a transversal direct magnetic field (B ≦ 1.4 T) has been measured and compared. Within the detection limit no reproducible effect was observed with Me = Zn, Cu, and Fe. A small growth acceleration occured in case of Ni(NH₄)₂(SO₄)₂ · 6 H₂O. The results which will be completed by measurements at higher magnetic flux densities, support the viewpoint that the application of magnetic fields on crystallization of diamagnetic substances from solutions offers no real advantage.     

Compositional dependence of morphology and lattice parameters during growth of K1‐x(NH4)xH2PO4 mixed crystals

Mixed crystals of ammonium dihydrogen phosphate and potassium dihydrogen phosphate K_1‐x(NH₄)_x H₂PO₄ were grown from aqueous solutions with x = 0.06, 0.09, 0.15, 0.32, 0.42, 0.51, 0.63, 0.70, 0.76, 0.78, 0.84, 0.88, 0.89 and 0.91. The crystal composition that differs from solution was estimated by X‐ray method. Morphology of the crystals changes from tetragonal prism to needles when the incorporation of either of the two components into the other; which also affects the growth rate along the prominent growth directions significantly. Growth along the [001] decreases initially with composition and reached the maximum when x = 0.5; whereas growth along the [100] always showed a decreasing trend with composition and attained a minimum value when x = 0.5. Crystal length along the [001] and [100] and aspect ratio are also compositional dependent. Unit cell parameters determined by X‐ray powder and single crystal analyses revealed that the ‘a ’ parameter shows only a small and linear variation but the ‘c ’ parameter changes significantly with ADP incorporation because of the difference in the effective ionic radius of K⁺ and NH₄⁺ ions and also the possibility of NH₄⁺ ion to form two different kinds of hydrogen bonds in the system. The existence of a pseudo‐cubic cell at the mixing composition x = 0.78 was also revealed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Iso‐Diameter Growth of β ‐BaB2O4 (BBO) Crystals by Flux Pulling Method

The iso‐diameter growth of β ‐BaB₂O₄ (BBO) crystals by the flux pulling method have been studied based on the phase equilibrium diagram in the BaB₂O₄‐Na₂O pseudo‐binary system and from the interface stability. The mathematical expressions for the cooling rate in the growth of the crystals with constant diameter under stable growth conditions are derived, the experimental phenomena such as diameter contraction and difficulty to grow a lengthy crystal by the flux pulling method are explained, the prerequisite for iso‐diameter BBO crystal growth from the flux is suggested; a new continuous charging flux pulling method is introduced to grow large‐sized high quality crystals with a relative high growth rate.     

Crystal growth and structure of KBi(WO4)2 single crystals

Potassium bismuth tungstate [KBi(WO₄)₂] single crystals have been grown by the top‐seeded solution growth technique. Bulk crystal with dimensions up to several centimeters is obtained for the first time. Several self‐flux systems have been used for the growth from the solution and the experiments using K₂W₂O₇ as a solvent are detailed. Powder and single crystal X‐ray diffraction of this crystal are reported. The structure refinement shows that KBi(WO₄)₂ crystallizes in the monoclinic space group C2/c, with a=10.837(3), b=10.586(3), c=7.622(2)Å, β=130.860(3)°, V=661.4(3)ų, and Z=4. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of KBi(WO4)2 single crystals

Potassium bismuth tungstate [KBi(WO₄)₂] single crystals with dimensions up to 20 mm × 15 mm × 15 mm have been successfully grown by using the top‐seeded solution growth technique and K₂W₂O₇ as solvent. Experiments show that this crystal is unstable in a strong acid or alkali environment and has a blue fluorescence emission. The density, hardness, melting point, absorption edge, transparency range, prominent Raman shift frequency are 7.57 g/cm³, 238 kg/mm², 800 °C, 380 nm, 400–5450 nm, 868 cm^–1 respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)