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The MgO-MgAl2O4 eutectic was directionally solidified via micro-pulling down method in the form of rods with 2–3 mm diameter. MgAl2O4 single crystals (with orientation) were used as crystallization seeds. At low pulling rates, especially 0.15 mm/min triangle-like cross-section was observed, which was linked to the eutectic MgAl2O4 following the crystallographic direction of the seed. MgO precipitates in the form of lamellae and rods with median equivalent diameter ranging from 0.19 to 0.85 μm, depending on the pulling rate. The preferred crystallization direction was for both phases, however notable traces of other directions, e.g. , and were found as well.

International audience; Al2O3-YAG-ZrO2 eutectic ceramic rods of 5 mm in diameter were grown by micro-pulling down technique. The seeding and the solidification rate affect microstructure, morphology, crystallography, and thermal stress of the solidified ceramics. The ternary eutectic grown through zirconia (111) seed had inhomogeneous and irregular cellular microstructures. At the stationary stable regime, the microstructure spacing (λ) depends on the pulling rate (v). Under solidification rate of 0.5 mm.min−1, the rods grown by using eutectic poly-crystal, (100), (111) YAG, and c(0001), A(1−210), M(10−10) sapphire seeds, the YAG and ZrO2 phases are oriented along the direction parallel to the growth direction. The zirconia (111) seeding X-ray diagram eutectic presents additional peaks and the monoclinic ZrO2 phase appears at the solidification rate of 1 mm.min-1. The rods grown through ZrO2 seeding are more stressed than those solidified by using eutectic, YAG and sapphire seeds, respectively.

International audience; Spectroscopic and luminescent properties of europium (Eu), erbium (Er), thulium (Tm) doped LiGd(WO4)2 fibers crystals, present high performances for investigation in phosphorus and laser applications. We have successfully grown 2 at % Eu, Er and Tm-doped LiGd(WO4)2 singles-crystals fibers by the Micro Pulling Down (μ-PD) technique (melting point above 1115 °C) using a pulling rate in the range of 0.08–0.15 mm/min. The crystallization interface was flat, with meniscus length equal to the fiber radii. The absorption and emission spectra were measured at room temperature. The absorption and emission cross sections of the Eu3+, Er3+, and Tm3+ transitions were evaluated. For the erbium cation we register 4S3/2 → 4I15/2, 2H11/2 → 4I15/2 transitions in the visible and 4I13/2 → 4I15/2 in IR range. The emission spectra recorded in the visible and infrared range with fluorescence correspond to 1G4→3F4 +3F2, 3F3→ 3H6, 3H4 → 3H6, and 1G4 → 3H5 for the thulium, instead for the europium we have 5D1→7F1,2 and 5D0 → 7F0-1-2-3-4, transitions. This last one presents an excellent structural probe for investigating the local environment of Eu3+ dopant in LiGd(WO4)2 host. The fluorescence lifetimes associated to these intense transitions were investigated. The polarized IR and Raman spectra of LiGd (WO4)2 single crystal fiber were measured, parallel and perpendicular to the fibers growth direction. We observed a bonds at 915 cm-1 for IR and 913 cm-1 for Raman corresponding of the symmetric stretching mode of the isolated tetrahedra (WO4)-2 group.

This paper addresses several aspects of the µ-PD growth technology as applied to submillimeter diameter sapphire tubes for UFD application. The μ-PD method has been successfully adapted for single crystal sapphire tube growth. A compound crucible made possible the growth of single crystal sapphire tube as small as around 0.70–0.72 mm in outer diameter and 0.28–0.29 in inner diameter over 160 mm in length at growth rate of 2–4 mm/min along 〈0 0 1〉 direction. An Ir crucible with a die composed of an equivalent hole and Ir wire was heated by RF coil in N2 atmosphere. The μ-PD method has been successfully adapted for single crystal sapphire tube growth. Grown crystal tube showed good XRC value of 30.2 arcsec.

During crystal growth in heat exchanger method (HEM) system, the shape of the growth interface changes with the proceeding of the growth process, which limits the crystal size and reduces the quality of the crystal. In this paper, a modified HEM system is proposed to control the interface shape for growth of sesquioxide crystals. Numerical simulation is performed to predict heat transfer, melt flow and interface shape during growth of high melting sesquioxide crystals by the heat exchanger method. The results show that a flat or slightly convex interface shape is beneficial to reduce the solute pileup in front of the melt/crystal interface and decrease the radial temperature gradient inside the crystal during growth of sesquioxide crystals. The interface shape can be controlled by adjusting the gap size d and lower resistance heater power during growth. The growth rate and the melt/crystal interface position can be obtained by two measured temperatures.

Cross-sectional shape-controlled Fe-Ga alloy crystals for energy harvester applications were grown using the micro pulling down (μ-PD) method. The investigation of material concentrations along the growth direction reveals that a high growth rate of 5.0 mm/min raises the effective segregation coefficient of Ga, k eff (Ga), and ensures high concentration homogeneity. However, the high growth rate was speculated as causing non-preferentially oriented portion formation that decreases the magnetostrictive property. The magnetostriction 3/2λ = 286 ppm was achieved for a good oriented sample (i.e. the misorientations from 〈100〉 were less than 7.5°.) with the Ga concentration of 16.8 at%. A prototype vibration energy harvester using a plate-shaped Fe-Ga alloy grown at 5.0 mm/min showed comparable or superior performance to the device using commercially available alloys. By leveraging the advantages of near net-shape controlling and a higher growth rate than other crystal growth techniques, the μ-PD method is expected to emerge as a new technique for mass-producing Fe-Ga alloys as materials for energy harvester applications.

La2Zr2O7 crystals with a melting point of 2283 °C are grown via the micro-pulling-down (μ-PD) method using Mo and W crucibles to expand the possibility of material research of functional single crystals with high melting points by the μ-PD method. La2Zr2O7 crystals grown using Mo and W crucibles under an Ar + 3% H2 atmosphere are composed of a La2Zr2O7 main phase, which includes Mo and W. However, a La2Zr2O7 crystal without W can be grown under an Ar atmosphere using the μ-PD method using a W crucible and deoxygenated ZrO2 insulators. After post-annealing in air at 1000 °C, the La2Zr2O7 crystal without W becomes colorless and transparent, indicating a transmittance exceeding 70% in wavelengths ranging from 450 to 800 nm.

A surface crack defect is normally found in low pressure castings of Al alloy with a sudden contraction structure. To further understand the formation mechanism of the defect, the mold filling process is simulated by a two-phase flow model. The experimental results indicate that the main reason for the defect deformation is the mismatching between the height of liquid surface in the mold and pressure in the crucible. In the case of filling, a sudden contraction structure with an area ratio smaller than 0.5 is obtained, and the velocity of the liquid front increases dramatically with the influence of inertia. Meanwhile, the pressurizing speed in the crucible remains unchanged, resulting in the pressure not being able to support the height of the liquid level. Then the liquid metal flows back to the crucible and forms a relatively thin layer solidification shell on the mold wall. With the increasing pressure in the crucible, the liquid level rises again, engulfing the shell and leading to a surface crack. As the filling velocity is characterized by the damping oscillations, surface cracks will form at different heights. The results shed light on designing a suitable pressurizing speed for the low pressure casting process.

In the present work, a combined 2D-3D numerical simulation was performed to study the effect of shape change in the graphite crucible on the heat transfer, flow pattern, mass transport, and electromagnetic field during top seeded solution growth of SiC considering the dissolution of carbon during crystal growth. The graphite crucible shapes at each growth process time were predicted using 2D axisymmetric steady global heat and mass transfer simulations. The crucible geometries obtained for each time step, including the predicted crucible shapes, were used for 3D unsteady simulations. The investigation revealed a significant effect of the shape change of the crucible on the temperature, Lorentz force distribution induced by the radiofrequency heating system, flow pattern, carbon concentration in the solution, and growth rate of SiC.

International audience; Single La3Ga5.5Ta0.5O14 (LGT) crystals have been grown by using the Czochralski technique with inductive heating. Some ingots exhibit imperfections such as cracks, dislocations and striations. Numerical modeling is applied to investigate the factors affecting the shape of the crystal-melt interface during the crystallization of ingots having 3 cm in diameter. It was found that the conical shape of the interface depends essentially on the internal radiative exchanges in the semi-transparent LGT crystal. Numerical results are compared to experimental visualization of the growth interface, showing a good agreement. The effect of the forced convection produced by the crystal and crucible rotation is numerically investigated at various rotation rates. Increasing the crystal rotation rate up to 50 rpm has a significant flattening effect on the interface shape. Applying only crucible rotation enhances the downward flow underneath the crystal, leading to an increased interface curvature. Counter rotation between the crystal and the crucible results in a distorted shape of the interface. (C) 2017 Elsevier B.V. All rights reserved.

Two iridium crucibles with one and five capillaries at a nozzle were developed for the growth of Ce-doped Y3Al5O12 [Ce:YAG] single crystals by the micro-pulling-down [μ-PD] method. The purpose of the study was to examine the effect of the capillary number on the Ce distribution in the radial direction of the crystals. The crystals grown from 2 mol% and 5 mol% Ce-doped YAG melts were then cut perpendicular to the growth direction and polished to produce specimens suitable for the measurement of Ce distribution. The Ce:YAG crystals grown using the crucible with one capillary [Ce:YAG(1 C)] had greater Ce content in the central portion of the crystal when compared to its peripheral parts. On the other hand, in the case of the Ce:YAG crystal grown using the crucible with five capillaries [Ce:YAG(5 C)], the increased Ce concentration was detected in five specimen sections positioned just below the capillaries. The results indicated that increase of the number of capillaries is effective practice that results in an improvement of the radial homogeneity of the single crystals grown by the μ-PD method.

We numerically investigate the melt-crystal interface shape during the early stage of the solidification process when the crystal diameter increases. The contact angle between the melt-crystal interface and the crucible bottom wall is found obtuse during this stage, which is unfavorable for the crystal quality. We found that the obtuse contact angle is caused by the thermal resistance difference between the sapphire crystal and melt as well as the insufficient cooling effect of the crucible bottom. Two approaches are proposed to suppress the obtuse contact angle. The first approach is to increase the emissivity of the outer surface of crucible bottom. The second approach is to install a heat shield near the crucible bottom. The reduction of the emissivity of the heat shield is also favorable for the suppression of the obtuse contact angle. Compared with the increase of the emissivity of the crucible bottom, the installation of a heat shield is a more effective approach to prevent the appearance of an obtuse contact angle for the sake of reliability since a molybdenum heat shield can be reused and will not induce other impurities.

The noncontact crucible (NOC) method was proposed for obtaining Si single bulk crystals with a large diameter and volume using a cast furnace and solar cells with high conversion efficiency and yield. This method has several novel characteristics that originate from its key feature that ingots can be grown inside a Si melt without contact with a crucible wall. Si ingots for solar cells were grown by utilizing the merits resulting from these characteristics. Single ingots with high quality were grown by the NOC method after furnace cleaning, and the minority carrier lifetime was measured to investigate reduction of the number of impurities. A p -type ingot with a convex growth interface in the growth direction was also grown after furnace cleaning. For p -type solar cells prepared using wafers cut from the ingot, the highest and average conversion efficiencies were 19.14% and 19.0%, respectively, which were obtained using the same solar cell structure and process as those employed to obtain a conversion efficiency of 19.1% for a p -type Czochralski (CZ) wafer. Using the cast furnace, solar cells with a conversion efficiency and yield as high as those of CZ solar cells were obtained by the NOC method.

Platinum (Pt) crystalline fibers were grown from the melt by the micro-pulling-down (μ-PD) method using the ZrO 2 ceramics crucible. The diameter of the grown Pt fiber was controlled by the ϕ1 mm outlet made at the bottom of the crucible and the Pt fiber of 0.95±0.03 mm in diameter and over 5 m in length was obtained at 10 mm/min pulling-down rate. In addition, the Pt fiber was grown at 1–110 mm/min pulling rates while the liquid-solid interface reached the bottom of the crucible and the crystal growth became unstable at 120 mm/min pulling rate. Few grain boundaries were observed in the scanning electron microscopy image of the Pt fibers and there were some spots with high intensity in the pole figures.

In this study, the effect of the temperature and flow fields generated by the rotation of the crucible and the crystal on the convexity of a c-axis, large-diameter sapphire crystal during the Czochralski growth process is investigated numerically. The thermal stress distributions in different sizes of crystal are also considered. The computational results show that the convexity and the thermal stress of the crystal are strongly dependent on the crucible and crystal rotation rates. The counter rotation between the crucible and the crystal results in a flatter crystal-melt interface, compared to the case of no crucible rotation or crystal rotation. Maximum thermal stress occurs at the highest curvature of the crystal-melt interface which appears near the center of the growing crystal, and the value is directly proportional to the crystal's size. Moreover, there is a significant decrease in the von Mises stress for the crystal-melt interface with lower convexity due to a reduction in the temperature gradient in the radial direction along the interface. As the crystal length gets larger, the maximum von Mises stress rapidly reduces.

We employ finite-element modeling to assess the effects of the accelerated crucible rotation technique (ACRT) on cadmium zinc telluride (CZT) crystals grown from a gradient freeze system. Via consideration of tellurium segregation and transport, we show, for the first time, that steady growth from a tellurium-rich melt produces persistent undercooling in front of the growth interface, likely leading to morphological instability. The application of ACRT rearranges melt flows and tellurium transport but, in contrast to conventional wisdom, does not altogether eliminate undercooling of the melt. Rather, a much more complicated picture arises, where spatio-temporal realignment of undercooled melt may act to locally suppress instability. A better understanding of these mechanisms and quantification of their overall effects will allow for future growth optimization.

Numerical analysis is an effective tool to research the industrial Czochralski (CZ) crystal growth aiming to improve crystal quality and reduce manufacturing costs. In this study, a set of global simulations were carried out to investigate the effect of crystal-crucible rotation and pulling rate on melt convection and solid–liquid (SL) interface shape. Through analyses of the simulation data, it is found that the interface deformation and inherent stress increase during the crystal growth process. The interface deflection increases from 7.4 to 51.3 mm with an increase in crystal size from 150 to 400 mm. In addition, the SL interface shape and flow pattern are sensitive to pulling rate and rotation rate. Reducing pulling rate can flat SL interface shape and add energy-consuming. Interface with low deflection can be achieved by adopting certain combination of crystal and crucible rotation rates. The effect of crystal rotation on SL interface shape is less significant at higher crucible rotation rates.

A three-dimensional simulation model is used to study the oxygen concentration distribution in silicon crystal during the Czochralski growth process under a transverse uniform magnetic field. The flow, temperature, and oxygen concentration distributions inside the furnace are calculated for different crystal lengths. There is significant variation in the flow structure in the melt with the growth length. The results show that in the initial stages, there is a decrease in the oxygen concentration at the crystal-melt interface as the length of the growing crystal increases. As the crystal lengthens further, a minimum value is reached after which the oxygen concentration increases continuously. This trend is consistent with that shown in the experimental results. The variation of the oxygen concentration with the growth length is strongly related to the depth of the melt in the crucible and the flow structure inside the melt. Better uniformity of the axial oxygen concentration can be achieved by proper adjustment of the crucible rotation rate during the growth process.

N-benzyl-2-methyl-4-nitroaniline (BNA) fiber single crystals were grown by the micro-pulling down (µ-PD) method. Crucible material and its shape were selected based on wetting of the crucible material by liquid BNA. As a result, BNA fiber single crystal with about 1–2 mm diameter was successfully grown. Powder XRD analysis and X-ray rocking curve measurements were performed. Widely-tunable THz-wave generation from 4 THz to 14 THz was demonstrated using the BNA fiber crystal grown by µ-PD method.

A vertical Bridgman (VB) crystal growth process was established using modified micro-pulling-down (μ-PD) crystal growth system with a removable chamber that was developed for the growth of deliquescent halide single crystals because conventional μ-PD method does not allow growth of large bulk single crystals. Eu:SrI2 crystals were grown from the melt of (Sr0.98Eu0.02)I2 composition using carbon crucibles. Undoped μ-PD SrI2 crystals were used as seeds that were affixed to the bottom of the crucible. All the preparations preceding the growths and the hot zone assembling were performed in a glove box with Ar gas. Then the removable chamber was taken out of the glove box, attached to the μ-PD system, connected with a Turbo Molecular pump, and evacuated down to 10−4 Pa at ~300 °C. After the baking procedure, high purity Ar gas (6N) was injected into the chamber. The crucible was heated by a high frequency induction coil up to the melting point of Eu:SrI2. After melting the starting materials, the crucible was displaced in downward direction for the crystal growth and then cooled down to room temperature. Thus, 2 in. and crack-free Eu:SrI2 bulk crystals were produced. The crystals had high transparency and did not contain any visible inclusions. The crystals were cut and polished in the glove box and then sealed in an aluminum container with an optical window for characterization. The details of the crystal growth are discussed.

Growth of 2-in. diameter Ce-doped (La , Gd) 2 Si 2 O 7 (La-GPS) scintillating crystals by Czochralski method using Ir crucible is reported. The composition of the host material was approximately equal to La 0.5 Gd 1.5 Si 2 O 7 and the concentration of the Ce 3+ -activator was either 0.5 or 1.5 at.% with respect to the total content of the rare-earths forming the host crystal matrix. Effects of the hot zone construction including inductive coil position, presence/absence of the after-heater, rotation rate and other growth parameters on the crystal quality are discussed in some details. The crystals produced in optimized conditions were colorless, transparent, uniform in their shape, crack- and inclusions-free, and demonstrated smooth glass-like surface. The length of the crystals’ cylindrically-shaped body parts exceed 100 mm. The growth results were well reproducible. The main disadvantage of the growth process is associated with short lifetime of the Ir crucible and its deformation caused by thermal expansion of the pre-solidified melt at each heating stage.

In this study, the installation of insulation blocks in the hot zone is utilized to assist in the growth of multi-crystalline silicon ingots with 800 kg of silicon charge using the seeded directional solidification method. A transient global numerical simulation is carried out to investigate the heat and mass transport during growth process. At a higher solidification fraction, lower concavity of the crystal–melt interface near the crucible wall can be obtained as compared to the standard model. The lowest concavity and highest energy saving is achieved when insulation blocks are added to the side of a directional solidification block and to the low part of the side insulation. The simulation results for this design also show a reduction of the melt velocity. The average oxygen concentration is slightly higher along the crystal–melt interface, compared to the standard one.

Small wustite (Fe1−xO) crystals were grown using the micro-pulling-down technique. Eutectoid decomposition of the grown crystals was suppressed by fast cooling associated with fast crystal pulling at a rate of 50 mm/min. Crystals grown at lower rates contained magnetite as a second phase indicating the beginning decomposition. Additionally, in those crystals the original wustite of near-eutectoid composition ( x ≈ 0.05 ) was decomposed into two wustite phases of which one was iron-poor, x ≈ 0.09 , the other instead iron-rich, near-stoichiometric, x ≈ 0.02 .

A new approach to β-Ga 2 O 3 single crystal growth was studied, using the vertical Bridgman (VB) method in ambient air, while measuring the β-Ga 2 O 3 melting temperature and investigating the effects of crucible composition and shape. β-Ga 2 O 3 single crystals 25 mm in diameter were grown in platinum–rhodium alloy crucibles in ambient air, with no adhesion of the crystals to the crucible wall. Single crystal growth without a crystal seed was realized by (100) faceted growth with a growth direction perpendicular to the (100) faceted plane.

We carried out global transient simulation of impurity distribution in multi-crystalline silicon grown by directional solidification using appropriate software. Non-metallic impurities such as carbon, nitrogen and oxygen originate from the furnace parts and each impurity atom was segregated into the mc-Si ingot based on their solubility in the crystal. During the solidification process the temperature distribution causes melt fluctuation in the Si melt, which is controlled by applying an external body force that leads to a uniform distribution of impurity atoms. Here the uniform distribution of impurity atoms was obtained by rotating the crucible at 10 rpm and the investigations were also carried out without crucible rotation and with a crucible rotation rate of 3 rpm. In this paper we have analyzed the segregation of non-metallic impurity atoms and chemical reactions between the impurity atoms, wherein three types of simulations were carried out and their results analyzed.

Oxygen and carbon are the most common impurities in multi-crystalline silicon. The general mechanism for formation and transport of O and C in the solidification furnace is as follows: oxygen from the silica crucible comes into the melt and combines with a silicon atom and evaporates at the gas/melt interface in the form of silicon oxide (SiO). Argon inert gas, injected into the furnace chamber, carries the SiO to the hot graphite fixtures, where it reacts with carbon to form carbon monoxide (CO) and silicon carbide (SiC). CO is carried by the gas to the melt free surface, where it dissociates into carbon and oxygen. Finally, during solidification oxygen and carbon are incorporated into the crystal. A global furnace model accounting for heat transfer, melt flow, gas flow and impurity transport has been applied to investigate the oxygen and carbon formation and transport in a vertical Bridgman furnace during the holding phase when the furnace is at its hottest. A case study is performed to investigate the effect of the applied heating power on the carbon and oxygen concentrations in the melt prior to solidification.

The effect of accelerated crucible rotation technique (ACRT) on liquid phase diffusion (LPD) growth of Si x Ge 1− x crystal has been investigated numerically. Transient, axisymmetric simulations have been carried out for triangular and trapezoidal ACRT cycles. Natural convection driven flow in the early growth hours is found to be modified by the ACRT induced Ekman flow. Results also reveal that a substantial mixing in the solution can be induced by the application of ACRT in the later hours of growth which is otherwise a diffusion dominated growth period for LPD growth technique. A comparison is drawn to the cases of stationary crucible and crucible rotating at a constant speed examined previously for this growth system by Sekhon and Dost (J. Cryst. Growth 430 (2015) 63). It is found that a superior interface flattening effect and radial compositional uniformity along the growth interface can be accomplished by employing ACRT at 12 rpm than that which could be achieved by using steady crucible rotation at 25 rpm, owing to the higher time averaged growth velocity achieved in the former case. Furthermore, minor differences are also predicted in the results obtained for trapezoidal and triangular ACRT cycles.

A series of experiments are presented to understand the effects of crystal and crucible rotations on the thermal convection in a model Czochralski (Cz) configuration which consists of a crucible filled with the transparent 0.65 cSt silicone oil ( Pr =6.7) and a model crystal. The thermal convection is induced by the temperature difference between the crucible sidewall and the crystal sidewall. The results show that the critical Rayleigh number for the onset of instability of thermal convection increases with the increase of the crystal rotation rate without the crucible rotation. When the crucible rotates, the critical Rayleigh number is higher than that with standing crucible at small crystal rotation rates. After the flow destabilizes, a three-dimensional oscillatory convection is characterized by traveling spoke patterns at small crystal rotation rates. With the increase of the crystal rotation rate, the azimuthal propagating velocity of the spoke pattern increases. Furthermore, the spoke pattern dims gradually and gives way to the wave pattern. The crystal rotation has a slight effect on the spoke number until the spoke pattern disappears. Compared with the shallow pool, the crystal rotation makes the flow more likely to be disturbed in the deeper pool. On the contrary, the crucible rotation is more conducive to suppressing the oscillatory flow in the deeper pool.

Bulk single crystals of the perovskite Li x La (1− x )/3 NbO 3 , which is one of the materials used as the solid electrolyte in all-solid lithium-ion batteries, have been grown for the first time by the directional solidification method. The ionic conductivity measured in the growth direction of a single crystal wafer of Li x La (1− x )/3 NbO 3 with x =0.08 showed a maximum value of 1.9×10 −4 Scm −1 .

To improve the dopant homogeneity in the radial direction, the micro-pulling-down apparatus was modified for Ce-doped Y 3 Al 5 O 12 (Ce 3+ :YAG) crystal growth. Two effective crucible variants, diffusion-channel and multi-channel crucibles, were adopted to alleviate the inhomogeneity of dopant concentration in the radial direction. In the diffusion-channel model, two different inclination angles were investigated. The results demonstrate that the radial dopant distribution at the melt-crystal interface (i.e., the growth front) is improved notably by using the diffusion-channel crucible. Furthermore, the better radial distribution is achieved with the larger inclination angle. In the multi-channel model, more capillary–channels result in a smaller inflow velocity from every single capillary-channel with the same growth rate. Therefore, the effect of inflow on the dopant distribution is reduced, and thus the radial dopant homogeneity is improved apparently. Besides, although the symmetry of concentration distribution along the azimuthal direction is broken in the multi-channel model, the whole homogeneity of dopant at the melt-crystal interface is ameliorated.

A process of vacuum melting of quartz glass with the crucible filled quartz grit layer by layer is described. The experimental results attest fewer defects and greater light transmission in quartz glass obtained by layering.

Single crystal scintillators are extensively used in various radiation detection applications and their scintillation performances can be improved via co-doping. Therefore, in this study, tungsten-ion co-doped Ce:Gd3(Ga,Al)5O12 (Ce:GGAG) crystals were grown using the micro-pulling-down (μ-PD) method to investigate the effects of co-doping on their scintillation properties. The relationships between the W concentration, optical and luminescence properties, and radiation response of the W-co-doped Ce:GGAG crystals were evaluated. The W-co-doped Ce 0.5%:Gd3Ga3Al2O12 single crystals of diameter 3 mm and length 30–60 mm were grown by the μ-PD method. The light yield increased at W concentrations of 200 and 500 ppm and decreased at W concentrations above 1000 ppm. There was no significant change in the fast decay component of scintillation.

A numerical simulation study has been carried out to investigate the influence of steady crucible rotation on the LPD growth of SixGe1−x. Results reveal the effectiveness of suppressing natural convection driven flows with the application of ampoule rotation. Improvement in the uniformity of radial composition of the growing crystal is predicted after two hours of growth for the remaining simulated growth period. Further, a marginal reduction in the growth interface curvature due to crucible rotation is also observed in the results. Numerical computation shows the potential of crucible rotation as a viable alternative to static magnetic field in inhibiting buoyancy induced flows in the LPD growth of SixGe1−x.

Separation and purification of the Si crystal during solidification process of hypereutectic Al–30Si melt under traveling magnetic field (TMF) were investigated in the present study. The results showed that under a proper condition the Si-rich layer can be formed in the periphery of the ingot while the inner microstructure is mainly the Al–Si eutectic structure. The intense melt flow carries the bulk liquid with higher Si content to promote the growth of the primary Si phase which is first precipitated close to the inner wall of the crucible with a relatively lower temperature, which resulting in the remarkable segregation of the primary Si phase. The impurity contents of the refined Si can be reduced to a very low level. The typical metallic impurities have removal fraction higher than 99.5%. In addition, there is a significant difference in the P contents between the primary and eutectic Si phases, which might be ascribed to the formation of AlP phase that acts as the heterogeneous nucleation sites. Furthermore, a considerable amount of Fe-containing particles with a size about 100–300 nm is found inside the eutectic Si phase, indicating an unintended entrapment of Fe in Si.

A 2D finite element method is employed to compute electromagnetic field as well as volumetric heat generation in an oxide Czochralski crystal growth system considering different shapes of metal crucible and different configurations of induction coil. The results show undeniable roles of crucible corner shape and setup of the RF-coil under the crucible in producing desirable heat pattern and avoiding common issues in the CZ growth systems.

Two popular materials for multicrystalline Si ingot growth of the PV industry, Si 3 N 4 and fused quartz, are working as composited material, tested and used to make industrial scale crucible. The main purpose of this composite material is to working as crucible for overcoming the low thermal conductivity of single fused quartz crucible during Si ingot process. Certain ceramic properties tests of the composite material, like porosity, density, are done with various percent of Si 3 N 4 /fused quartz, and thermal shock test did as well. These results prove that our composite material is feasible to make square crucible for Si ingot process. Thus we simulate multicrystalline Si ingot growth and experiments are done by industrial scale G5 crucible made by the composite material with optimal ratio of Si 3 N 4 /fused quartz. These results show that since composite crucible has higher thermal conductivity, the more heat flux could penetrate the bottom of crucible for Si directional solidification, correspondingly the temperature distribution, interface of solid-liquid Si, growth speed and grain structure, these kinds of key features of Si ingot process can be improved. The thermal profile analysis and photoluminescence picture show the improvement of Si ingot process using this composite crucible. Finally the considerations of industrial mass production using this kind of composite crucible are discussed.

Flux growth involves dissolving the components of the target compound in an appropriate flux at high temperatures and then crystallizing under supersaturation controlled by cooling or evaporating the flux. A refractory crucible is generally used to contain the high temperature melt. The reaction between the melt and crucible materials can modify the composition of the melt, which typically results in growth failure, or contaminates the crystals. Thus one principle in designing a flux growth is to select suitable flux and crucible materials thus to avoid any reaction between them. In this paper, we review two cases of flux growth in which the reaction between flux and Al$_2$O$_3$ crucible tunes the oxygen content in the melt and helps the crystallization of desired compositions. For the case of La$_5$Pb$_3$O, Al$_2$O$_3$ crucible oxidizes La to form a passivating La$_2$O$_3$ layer which not only prevents further oxidization of La in the melt but also provides [O] to the melt. For the case of La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$, it is believed that the Al$_2$O$_3$ crucible reacts with NaAsO$_2$ and the reaction consumes oxygen in the melt thus maintaining an oxygen-free environment., Comment: 5 pages, 4 figures, to appear in Journal of Crystal Growth

Due to the phase transition near 920 °C and hygroscopicity, the growth of BaCl 2 single crystals is difficult. However, owing to the suppression of the cubic–orthorhombic phase transition by La substitution and careful handling to prevent contact with the starting powders and moisture in the air, crack-free BaCl 2 single crystals were grown by the micro-pulling-down technique under ambient pressure. In addition, photo- and radio-luminescence in non-activated and Eu 2+ -activated compounds were reported for scintillator applications.

Ce-doped Lu2xGd2−2xSiO5 (LGSO:Ce) fiber-shaped crystals (x = 0.5) were grown by the micro-pulling down (µ-PD) technique. To optimize the activator concentration for achieving the best scintillation parameters, the cerium concentration in the melt was varied in the range from 0.01 to 1.5 at.%. Distributions of Gd3+ and Ce3+ in LGSO:Ce crystals grown by the µ-PD and Czochralski (Cz) techniques were compared. The spatial distribution of cations across the LGSO:Ce scintillation crystals grown by the µ-PD technique is studied using wide-field microscopy under simultaneous excitation of two types of Ce-related centers and confocal microscopy under the selective excitation of Ce3+ in CeO6 crystallographic sites. It is revealed that the fiber-shaped crystals contain a single crystal core surrounded by crystalline material with a higher density of inclusions and cracks that are predominantly directed along the crystal axis. The formation of inclusions and cracks is interpreted by a nonuniform radial distribution of LGSO:CE cations.

The carbon contamination of alloys prepared by the electro graphite crucible is impossible to avoid due to the inherit reaction between the melt and the crucible. In this study, the TiFe-based alloy is prepared by VIM process using CaO crucible as well as the electro graphite crucible. The samples are examined by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Energy Dispersive Spectrometer (EDS), and the PCT curves are also measured. It is resulted that, the oxygen content of alloys melted by CaO crucible is almost equal to the one melted by graphite crucible and without the carbon contamination, meanwhile the carbon content of alloys obtained by the electro graphite crucible is 1860 ppm, which exceeds the tolerance of the commercial alloy (1000 ppm). The microstructure of the alloy melted by CaO crucible is dendrite, while it is composed of the equiaxed crystal with the lamellar structure and the spherical TiC particles distributed along grain boundaries or within the grain when melted by the graphite crucible; the interfacial reaction of the electro graphite crucible with TiFe alloy melt is serious and the interaction layer is formed up to 200 μm in thickness, the carbon in TiFe-based alloys forms TiC. The hydrogen desorption plateau pressure of alloys melted by CaO crucible is (0.11–0.4) × 10 5 Pa, and that by the graphite crucible is (0.6–1) × 10 5 Pa. This may imply that the CaO crucible may be the promising candidate for melting the high performance TiFe based hydrogen storage alloys.

For certain semiconductors with important applications, the existing unseeded bulk directional solidification crystal growth technique from the melt usually results in poor quality multi-crystalline ingots which causes the low yield of the commercial growth process. The multi-grained crystal growth is mainly caused by the large supercool of the melt, which not only results in a large section of ingot solidifying uncontrollably under spontaneous nucleation but also prohibits the ideal growth condition that small single crystal nuclei form at the very tip of the ampoule and grow into large single grains. To promote nucleation under the condition of small supercooling, a method was employed to induce nucleation by mechanical perturbation at a critical time during growth. The technique was applied to the bulk crystal growth process of Cd 1− x Zn x Te ingots. The comparison between the crystalline quality of the crystals grown with and without the mechanically induced nucleation shows that the yield of single crystalline can been vastly improved with the application of the technique.

Experiments and numerical simulations are conducted in order to study the causes and solutions for the Ti inhomogeneity problem in Ti doped sapphire Micro-Pulling-Down (μ-PD) growth. The measurement and modeling of the thermal and flow fields, electromagnetic field, Ti concentration in the molten zone and along the fibre axis are compared. For the mean Ti concentration along the fibre and temperature along the iridium crucible, the modeling results are consistent with experiments. Results showed that for high pulling rate, the mass transfer in the capillary is dominated by convection. Marangoni convection is strong in the meniscus due to the large temperature gradient, which has great impact on the Ti distribution for different fibre radii. For high pulling rate, Ti concentration increases quickly from the seed along the fibre axis, and reaches a constant value after about 0.5–2 mm. Radial segregation is high for large diameter fibres. The constant Ti concentration along the fibre axis is increasing when increasing the fibre radius from 0.2 to 0.6 mm. For 0.8 mm, it decreases due to the change of the vortex. At low growth rate, the transport in the capillary is diffusive, back to the crucible, which leads to a Scheil-like Ti distribution, in full agreement with the experimental results.

Kyropoulos crystal growth seeding process for silicon was studied with 3D modeling of the full furnace. The process had three heating zones (top, bottom and side) to improve the control of the horizontal and vertical thermal gradients in the melt; and, a square crucible to reshape the final crystal into a square horizontal section. Modeling of the starting configuration, where crystal growth from the seed was not possible experimentally, explained that the ascendant melt flow in the center is bringing hot melt to the seed. The addition of a ceramic tube as a radiation shield around the seeding zone and the increase of side heating were modeled numerically as solutions to reverse the melt flow direction. The applied solutions on the experimental furnace allowed the growth from the seed. The process was sensitive to symmetry loss. The asymmetric growth of the crystal towards one preferential direction was explained by a coupling between the sudden increase of emissivity due to solidification of silicon and the local decrease of convection on the side of the preferred growth direction. A symmetric growth was obtained in the model by lowering radiative cooling at the top of the melt surface during the first stage of the growth, and by homogenizing the melt using crystal rotation. As a result, symmetrical circular crystals were obtained experimentally using the same growth conditions without contact with the crucible and with no upward pulling.

We propose a high-speed growth based on noncontact crucible method for obtaining large ingots with a constant diameter. In this method, the Si melt used has a large low-temperature region in its central upper part to ensure Si crystal growth inside it. Therefore, this method has the possibility of attaining a high growth rate using a high cooling rate because the growth rate is determined by the rate of expansion of the low-temperature region in the Si melt. The horizontal and vertical growth rates in Si melts were experimentally determined. At a cooling rate of 0.4 K/min, the horizontal growth rate reached 1.5 mm/min in the direction and 1.9 mm/min in the direction. These growth rates are higher than that of the cast method. The growth rate increased with the cooling rate. The vertical growth rate was determined to be 0.3–0.6 mm/min, and it tended to increase with increasing depth of the Si melt. The diameter of an ingot remained constant during pulling due to a high cooling rate of 0.4 K/min because the horizontal growth rate increased as the cooling rate increased and the melt temperature markedly decreased. An ingot with a constant diameter of 21 cm and a height of 7 cm was obtained inside a Si melt by the high speed growth using a crucible with 33 cm diameter.

A crucible cover is designed in a furnace for growing sapphire crystals by heat exchanger method. Global simulations of heat transfer are carried out to investigate its effects on the thermal field and melt flow in the crucible during the growth of sapphire crystal. It is found that the crucible cover has significant effect on the thermal field in the melt. When the crucible cover is installed, the radial temperature gradient in the melt at the melt–crystal interface decreases while the axial temperature gradient increases. The melt flow is weakened accordingly. The melt–crystal interface becomes flatter and the thermal stress in the crystal is reduced with the installed crucible cover. It can be therefore concluded that use of a crucible cover is favorable for crystal growth.

Ti-1100 alloys were melted in a controlled atmospheric induction furnace equipped with a CaO crucible. The microstructure, chemical composition, microhardness and metal–crucible interfacial reactions were systematically investigated. The results demonstrate that the primary solidification microstructure in the as-cast alloys was the typical Widmanstatten structure. The interactions between crucible and molten alloys are attributed to slight chemical dissolution and weak physical erosion. According to the line scanning analysis, the interfacial layer (α-case) thicknesses of Ti-1100 samples in the bottom and side wall are about 18 and 17 μm, respectively, which are slightly lower than those presented from microhardness tests (25 and 20 μm). The formation of α-case was caused by interstitial oxygen atoms. The standard Gibbs energy of reaction CaO(s)=Ca+O for Ti-1100 alloy was also determined. The equilibrium constant and the interaction parameter between calcium and oxygen were obtained as lg K=-3.14 and eCaO = 3.54.

We carried out transient global simulations of heating, melting, growing, annealing and cooling stages for the industrial directional solidification (DS) process. Two separate DS processes were performed with a covered crucible and an uncovered crucible to investigate the effect of a crucible cover on global heat transfer and silicon crystal growth. It is found that the cover blocks heat transfer from the heaters to the silicon domain significantly, and therefore influences the crystal growth through the entire DS process. For the melting of silicon feedstock, covering the crucible can lead to a significant increase in melting time, whereas it has little effect on the melting sequence. During the growing stage, the solidification time for the process with a crucible cover is much shorter than the process without a cover. The cover can also influence the melt convection near the free surface center, but it hardly changes the melt flow pattern deep in the crucible. For the annealing and cooling processes, heat transfer is not significantly affected by covering the crucible and the isotherm shapes in the silicon ingots are similar with and without a cover.

Growth of plate potassium niobate (KNbO3; KN) crystal from stoichiometric melt has been investigated by a micro-pulling-down (μ-PD) method. KN plate crystal with 1-2 mm×4-5 mm×35 mml dimensions was successfully grown using a platinum crucible with rectangular die of 4 mm×1 mm having a hole of 0.5 mm in diameter in its center. Obtained KN plate crystal did not contain K4Nb6O17 phase, coexisting with the potassium niobate phase when crystallization follows the phase equilibrium diagram. It appeared that sufficient supercooling was attained during the growth, and that the potassium niobate phase was stabilized in the melt. The parameters necessary for the reproducible growth of KN plate crystal were associated with a solid–liquid interface during the growth. Phase transition temperatures of the grown plate crystal agreed well with previously reported data, and sharp transitions were observed.

A small diameter Bridgman equipment was used to investigate the influence of two crucible materials (fused silica and graphite) and two coatings materials (Si3N4 and CaCl2) on the quality of the multicrystalline silicon ingots, with focus on the ingot detachment from crucible, grain size and orientation and precipitate formation. It was shown that using a CaCl2 encapsulating substance can lead to grains larger in size and more oriented along the axial growth direction for both the graphite and the fused silica crucible, although the detachment of the crystal from the crucible is only possible if a fused silica crucible was used. The layer of the SiC precipitates at the graphite crucible wall was found to be thinner if the CaCl2 encapsulant was used.

In this paper, we proposed a modified vacuum directional solidification system for producing multicrystalline silicon (mc-Si). A transient numerical model was carried out to simulate the process of mc-Si vacuum directional solidification which cannot be directly monitored. The temperature distribution, melt convection, melt–crystal (m/c) interface and thermal stress have been simulated. Simulation results show that the modified system is particularly suitable for growing high-quality crystal of mc-Si. The thermal stress of the silicon crystal decreases considerably due to the lower temperature gradient by installing a conical insulation unit, the m/c interface keeps slightly convex and the melt flow along the axis direction is relatively stronger by improving the heat transfer. The results of the experiment show that this modified system of mc-Si can obtain better crystal quality than the traditional vacuum directional solidification system.