Physical and physicochemical processes accompanying powder synthesis,growth of PbMoO<Subscript>4</Subscript> crystals,and their annealing in various media: II. Shape of the crystal-melt interface caused by melt evaporation and supercooling

The temperature distribution in a melt of PbMoO₄ is investigated using a modified thermocouple and a scanning device. It is shown that the PbMoO₄ melt whose thermal field is significantly inhomogeneous at different depths demonstrates a strong (below the melting temperature) supercooling at the surface due to the evaporation. The position of the isotherm corresponding to the melting temperature of PbMoO₄ in the melt is determined by the degree of the melt supercooling at different growth parameters. The results obtained show that the conditions of mass and heat exchange in the melt are mainly determined by convection. The free convection remains dominant even at intense rotation of a crystal and the most thorough thermal isolation of the crystallization unit.     

Optical,mechanical, and thermal properties of nonlinear LiKB<Subscript>4</Subscript>O<Subscript>7</Subscript> crystals

Nonlinear LiKB₄O₇ single crystals have been grown by the Czochralski method from a stoichiometric melt. The optical, acoustic, piezo-and electro-optical, and thermal properties of these single crystals have been studied.     

Structural state of a radiation-modified Ti<Subscript>50</Subscript>Ni<Subscript>47</Subscript>Fe<Subscript>3</Subscript> single crystal

The structural state of a Ti₅₀Ni₄₇Fe₃ single crystal irradiated by fast neutrons (F = 2.5 × 10²⁰ cm⁻²) at 340 K was studied by thermal neutron diffraction at 78 and 295 K. The melt of this composition was chosen with the purpose of designing a radiation-resistant material exhibiting a shape-memory effect. It was found that the melt remains crystalline after irradiation, whereas the Ti₄₉Ni₅₁ crystal studied earlier becomes amorphous after an analogous irradiation. In spite of the fact that the main structural motif of the crystal remains unchanged after irradiation, martensitic transformations in the crystal do not occur and, consequently, the shape-memory effect is not retained. The radiation resistance of this class of crystals was estimated.     

Melt nonstoichiometry and defect structure of ZnGeP<Subscript>2</Subscript> crystals

The defect structure of ZnGeP₂ crystals grown from a melt by the vertical Bridgman method has been investigated. A deviation of the melt composition from stoichiometric leads to the formation of striations and the inclusions of other phases which are observed as structures (chains) oriented parallel to the growth axis. According to the microanalysis data, the inclusion composition corresponds to a mixture of ZnGeP₂, Zn₃P₂, and Ge. Nanoinclusions of germanium phosphide are detected by transmission electron microscopy. X-ray topography reveals defects of four types. The main defects in the central part of an ingot are related to the composition fluctuations, and the newly formed dislocations are basically single ones. Most dislocations are formed at the crystal periphery.     

Melt Flow and Species Transport in μg‐Gradient‐Freeze Growth of Germanium

The result of a μg‐experiment on the Gradient‐Freeze growth of Ge:Zn with doping from the vapour phase shows a homogeneous distribution of the zinc in the melt, indicating the dominating role of a gravity‐independent transport mechanism. This effect is investigated numerically on the basis of a global model of the growth setup. The numerical simulation includes the melt flow and the transport of the dopant taking into account buoyant and thermocapillary forces. The results confirm the minor influence of gravity on the species transport. The complete mixing of the melt can be explained by thermocapillary (Marangoni) convection only.     

Growth and properties of ZnMoO<Subscript>4</Subscript> single crystals

The crystallization conditions for obtaining zinc molybdate single crystals by the Czochralski and Kyropoulos methods from a melt have been studied. The growth parameters of large single crystals of optical quality are determined. The physicochemical and spectral-luminescent characteristics of the single crystals are studied.     

Oxygen-conducting crystals of La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript>: Growth and main properties

Single crystals of the anionic conductor La₂Mo₂O₉ are grown by crystallization from a nonstoichiometric melt. Their polymorphism and domain structure, as well as the temperature dependences of conductivity and dielectric permittivity, are studied. In the temperature range 750–600°C, the conductivity of these crystals is as high as 10^?1–10^?2 Ω^?1 cm^?1.     

Study of melt dynamics in crystal growth of Pb1−xSnxTe by the inverted Bridgman method

Experiments with crystal growth of Pb_1−xSn_xTe by the inverted Bridgman method confirm the flow transition in the melt through succeeding stages of unsteady (turbulent) convection, periodically unsteady convection, one-vortex steady motion, two-vortex motion and in the end, lack of any detectable convection — in the range of Rayleigh numbers and ratios of melt height to ampoule diameter given by Müller et al. [J. Crystal Growth 70 (1984) 78]. Additionally, quasi-steady axially asymmetric flow between the first two stages has been observed. Its direction is opposite to the direction of the vortex formed in the subsequent stage of crystal growth. The two-vortex flow, beginning when the melt height equals the ampoule radius, is unsteady and periodically changes the liquid-solid interface shape.     

A new optical medium—Cd<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>F<Subscript>2</Subscript> single crystals

For the first time, single crystals of the Cd_0.75Sr_0.25F₂ solid solution with the fluorite structure are grown from melt by the Bridgman-Stockbarger method. The composition of these single crystals corresponds to the composition congruently melting at the minimum point on the phase diagram. The maximum diameter of the crystal is 50 mm; the maximum height is 30 mm. The vickers microhardness of the semitransparent crystals equals 191 ± 43 kg/mm². The transmission cutoff in the IR range is ～10 μm.     

Effect of ultrasound on the growth striation and electrical properties of Ga<Subscript>0.03</Subscript>In<Subscript>0.97</Subscript>Sb single crystals

The growth striation of impurity segregation and electrical properties of Ga_0.03In_0.97Sb single crystals grown by the Czochralski method in an ultrasonic field have been investigated. It is established that ultrasonic irradiation of the melt during growth significantly decreases the growth striation (in particular, it eliminates striations spaced at a distance of more than 14 μm). The Ga_0.03In_0.97Sb single crystals grown in an ultrasonic field had a higher charge-carrier mobility and thermoelectric power in comparison with the single crystals grown without ultrasound.     

The numerical simulation of heat and mass transfer during growth of a binary system by the travelling heater method

The influence of convection and heat and mass transfer on the shape and position of melt/solid interfaces and on radial composition segregation is analysed numerically for the travelling heater method growth of a binary alloy in a vertical transparent ampoule. Results are presented for crystal and melt with thermophysical properties similar to Cd_xHg_1−xTe with the assumption that the pseudobinary CdTe-HgTe phase diagram is true. The two-dimensional axisymmetric heat transfer equation, hydrodynamical equation and convective diffusion equation are included in the mathematical model. The rates of crystal growth and dissolution are supposed to be proportional to the compositional supercooling in the melt near the interfaces. It is shown for the conditions when convection is absent that the interfaces are asymmetrically positioned respectively to the heater centre line. Intensive convection makes their position more symmetrical but the length of the liquid zone greater. The flow pattern in the melt appears to be greatly influenced by solutal gravitational convection. The nonlinear dependence of the melt density on the temperature and composition are used in the model. The cases when speed of the heater is antiparallel (stable density stratification) or parallel (unstable stratification) to the vector of gravitational acceleration are considered.     

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.     

Growth of Cr<Superscript>4+</Superscript>: LiGaSiO<Subscript>4</Subscript> single crystals by floating-zone melting technique

The problems of growth of new promising laser crystals Cr⁴⁺: LiGaSiO₄ by the crucible-free floating-zone method with optical heating are considered. The use of high axial temperature gradients with intense stirring of the melt makes it possible to obtain crystals of satisfactory optical quality from stoichiometric melt, despite the incongruent character of the compound melting.     

ACRT forced convection and its effects on solute segregation and heat and mass transfer during single crystal growth

A numerical simulation study was carried out for CdZnTe vertical Bridgman method crystal growth with the accelerated crucible rotation technique (ACRT). The convection, heat and mass transfer in front of the solid‐liquid interface, and their effects on the solute segregation of the grown crystal can be characterized with the following. ACRT brings about a periodic forced convection in the melt, of which the intensity and the incidence are far above the ones of the natural convection without ACRT. This forced convection is of multiformity due to the changes of the ACRT parameters. It can result in the increases of both the solid‐liquid interface concavity and the temperature gradient of the melt in front of the solid‐liquid interface, of which magnitudes vary from a little to many times as the ACRT wave parameters change. It also enhances the mass transfer in the melt in a great deal, almost results in the complete uniformity of the solute distribution in the melt. With suitable wave parameters, ACRT forced convection decreases the radial solute segregation of the crystal in a great deal, even makes it disappear completely. However, it increases both the axial solute segregation and the radial one notably with bad wave parameters. An excellent single crystal could be gotten, of which the most part is with no segregation, by adjusting both the ACRT wave parameters and the crystal growth control parameters, e.g. the initial temperature of the melt, the temperature gradient, and the crucible withdrawal rate. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anisotropy of the Mechanical Properties of TbF<Subscript>3</Subscript> Crystals

TbF₃ (sp. gr. Pnma) crystals up to 40 mm in diameter have been grown from melt by a Bridgman technique. The anisotropy of their mechanical properties is studied for the first time. the technical elasticity constants are calculated, and room-temperature values of Vickers microhardness for the (010) and (100) planes are measured. The shape of indentation impressions is found to correlate with Young’s modulus anisotropy for TbF₃ crystals.     

Formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet grown by horizontal directed crystallization method

It is shown that the formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet (YAG) grown by the method of HDC is caused by local accumulation of impurities, disturbance of morphological stability of the crystallization front and capture of inclusions and impurities in the nodal region of the melt two‐vortex convection. Studied is the influence of thermal and geometrical parameters of the melt and the shape of the crystallization front on the conditions of the formation of the capture of inclusions.     

Influence of solidification of binary eutectic lamellar systems on surface tension driven convection in zero gravity conditions

The effect of solidification of the lamellar binary eutectic system on the onset of surface tension driven convection (so-called Marangoni instability) is studied in a zero gravity environment. Some main general conclusions concerning the possibility for onset of the Marangoni convection within the melt can be drawn from the analysis, viz., the curvature of the free surface has a destabilizing effect on the onset of the flow; the increased perturbed heat transfer rate from the system stabilizes the melt; the onset of the solutal Marangoni convection closely depends on the ratio of the lamellae half-widths and the solutal Marangoni instability is more sensitive against the perturbations than the temperature Marangoni one.     

Simulation of temperature and flow fields in an inductively heated melt growth system

The goal of the research presented here is to apply a global analysis of an inductively heated Czochralski furnace for a real sapphire crystal growth system and predict the characteristics of the temperature and flow fields in the system. To do it, for the beginning stage of a sapphire growth process, influence of melt and gas convection combined with radiative heat transfer on the temperature field of the system and the crystal‐melt interface have been studied numerically using the steady state two‐dimensional finite element method. For radiative heat transfer, internal radiation through the grown crystal and surface to surface radiation for the exposed surfaces have been taken into account. The numerical results demonstrate that there are a powerful vortex which arises from the natural convection in the melt and a strong and large vortex that flows upwards along the afterheater side wall and downwards along the seed and crystal sides in the gas part. In addition, a wavy shape has been observed for the crystal‐melt interface with a deflection towards the melt. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

旋转磁场对空间浮区内流场及浓度场的影响

采用全浮区模型数值研究了旋转磁场作用下熔区内热毛细对流流动特性,分析了磁场强度对流场及浓度场的影响.研究发现,无磁场时,熔体内杂质浓度场和流场呈现三涡胞对称振荡特征;温度场主要由扩散作用决定,呈对称分布.旋转磁场作用下,Ma数基本保持不变.当磁场强度B0≤1 mT时,熔体内杂质浓度场和流场与无磁场时结构类似,但旋转磁场的搅拌作用使得熔体内周期性振荡提前出现,且当旋转磁场产生的洛伦兹力相对较大时,表面张力产生的三维振荡对流得到很好地抑制.B0=5 mT时,周向波动被完全抑制,熔区内流场和浓度场呈二维轴对称分布.旋转磁场对熔体流动产生的轴向抑制作用和周向搅拌作用,都有助于熔体流动的稳定性、浓度分布以及温度分布的均匀性,从而有利于高质量晶体的生长.     

Numerical investigation of heat transport and fluid flow during the seeding process of oxide Czochralski crystal growth Part 2: rotating seed

In this paper, the role of seed rotation on the characteristics of the two‐dimensional temperature and flow field in the oxide Czochralski crystal growth system has been studied numerically for the seeding process. Based on the finite element method, a set of two‐dimensional quasi‐steady state numerical simulations were carried out to analyze the seed‐melt interface shape and heat transfer mechanism in a Czochralski furnace with different seed rotation rates: ω_seed = 5‐30 rpm. The results presented here demonstrate the important role played by the seed rotation for influencing the shape of the seed‐melt interface during the seeding process. The seed‐melt interface shape is quite sensitive to the convective heat transfer in the melt and gaseous domain. When the local flow close to the seed‐melt interface is formed mainly due to the natural convection and the Marangoni effect, the interface becomes convex towards the melt. When the local flow under the seed‐melt interface is of forced convection flow type (seed rotation), the interface becomes more concave towards the melt as the seed rotation rate (ω_seed) is increased. A linear variation of the interface deflection with respect to the seed rotation rate has been found, too. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)