Preparation Of Single Crystals Research Articles

Design and Development of Instrumentations for the Preparation of Platinum Single Crystals for Electrochemistry and Electrocatalysis Research. Part 2: Orientation, Cutting, and Annealing

In this contribution, which is the second paper in a series, we report on the design and development of several pieces of equipment, which facilitate the preparation of a hemispherical single crystal with a desired crystallographic surface structure starting with a spherical Pt single crystal. The pieces of equipment include a dual, high-resolution charge-coupled device (CCD)-based camera for acquiring Laue X-ray back-scattering patterns to orient spherical single crystals, a precision custom-designed jig for cutting and polishing pre-oriented single crystals, and an induction annealing system with controlled gaseous atmosphere for obtaining well-ordered and defect-free single crystal surfaces. Firstly, the paper describes the dual CCD camera setup, which allows acquiring, processing, and analyzing Laue back-scattering patterns in a digital format. The single crystal holder comprising a goniometer, the CCD-based detection system, and an optomechanical system together allow simple, adaptable, quick, and accurate single crystal orientation. Secondly, the paper presents details of a high-precision jig used in the cutting and polishing of single crystals. The jig setup includes a goniometer supporting a holder in which a single crystal is mounted and two micrometers. It maintains the desired single crystal surface parallel to the polishing disk on which abrasive materials are dispersed and polishing cloths are mounted. The micrometers allow monitoring the polishing rate and maintaining the desired single crystal surface exactly parallel to the polishing disk. Thirdly, the paper describes details of the annealing system. It consists of an induction-annealing furnace with a custom-made coil, a custom-designed quartz cell that facilitates single crystal annealing under controlled atmosphere conditions. Optimization of the induction annealing parameters and conditions, which determine the final quality of single crystal surfaces, is described in detail. Finally, the paper explains the unique aspects of this setup and methodically describes the operating procedures required to obtain a hemispherical single crystal with an atomically flat surface.

Infrared optical characterization and energy transfer of Na5Lu9F32 single crystals co-doped with Er3+/Tm3+ grown by Bridgman method

This paper reported on successful preparation of Na5Lu9F32 single crystals co-doped with ∼2mol% Er3+ and various Tm3+ concentrations from 0.7mol% to 3.2mol% by Bridgman method. The J-O intensity parameters of Er3+ were calculated and analyzed according to the absorption spectra. The fluorescence decay curve at Er3+:4I13/2 level was measured to investigate the luminescent properties of the Er3+/Tm3+ co-doped Na5Lu9F32, and the energy transfer process between Er3+ and Tm3+. An intense 2.7μm emission was achieved with Tm3+ ions sensitizing Er3+ ions under the 800nm LD pumping. The maximum emission intensity at 2.7μm was obtained at about 3.2mol% doping concentration of Tm3+ when the concentration of Er3+ ions was fixed at ∼2mol% in the current research. The calculated maximum value of emission cross section at 2.7μm was 2.22×10−20cm2, and energy transfer efficiency from Er3+:4I13/2 to Tm3+:3F4 was 78%. The electric dipole-dipole interaction was dominant for the energy transfer from Er3+ to Tm3+ ions by using Inokuti-Hirayama’s model.

Superconductivity and magnetic fluctuations developing in the vicinity of strong first-order magnetic transition in CrAs

We report single crystal preparation, resistivity, and nuclear quadrupole resonance (NQR) measurements for new pressure-induced superconductor CrAs. In the first part, we present the difference between crystals made by different thermal sequences and methods, and show the sample dependence of superconductivity in CrAs. In the latter part, we show NQR data focusing the microscopic electronic state at the phase boundary between the helimagnetic and the paramagnetic phases. They suggest strongly that a quantum critical point is absent on the pressure-temperature phase diagram of CrAs, because of the strong first-order character of the magnetic transition; however, the spin fluctuations are observed in the paramagnetic phase. The close relationship between the spin fluctuations and superconductivity can be seen even in the vicinity of the first-order magnetic transition in CrAs.

Ferroelectric glass-ceramics

Abstract

High-Temperature Flux Growth as a Tool for the Preparation of Mixed-Framework Metal-Y Silicates: A Systematic Evaluation of the Influence of Experimental Parameters

We report new aspects of the application of the flux-growth method for the preparation of single crystals of silicates, in particular, mixed-framework (octahedral–tetrahedral) metal-Y silicates, in air. The detailed investigations involve flux-growth syntheses in the system BaO–K2O–Y2O3–SiO2–MoO3, in which various important run parameters have been varied in a systematic way (heating and cooling rates, Tmax and duration of holding step, continuous or stepwise cooling, total duration of run, amount of MoO3 solvent, Y2O3/SiO2 molar ratio, size and filling volume of platinum crucible). The results demonstrate that the crystallization of various silicate structure types are strongly controlled by the Y2O3/SiO2 molar ratios and the amount of MoO3 solvent in the precursor mixtures. A decrease of the Y2O3/SiO2 ratio, i.e., an increasing amount of SiO2, promotes an increasing structural complexity of the silicates; nesosilicates crystallize at comparatively low SiO2 concentrations, sorosilicates at intermediate o...

Phase-field crystal modelling the nucleation processes of graphene structures on different substrates

Two-dimensional materials with unique and excellent physical and chemical properties have attracted much attention in recent years. Among the two-dimensional materials, graphene or grapheme-like materials with honeycomb structure can be mainly prepared by the chemical vapor deposition (CVD) method. The key of this method is to select the substrates and control the nucleation and growth process of honeycomb structures. Graphene prepared by CVD contains many structure defects and grain boundaries, which mainly arise from nucleation process. However, the nucleation mechanism of graphene prepared by CVD method is not very clear. In addition, more than ten kinds of metal substrates can be used as substrate materials in CVD methods, such as Cu and Ni, which have nearly always face-centered cubic (FCC) structures and similar functions in the preparation process. In order to better describe the nucleation of graphene and understand the influences of metal substrates, we introduce the structural order parameter into the three-mode phase-field crystal model to distinguish the low-density gas phase from condensed phases. Nucleation processes of graphene on substrates with different symmetries are studied at an atomic scale by using the three-mode phase-field crystal model, which can simulate transitions between highly correlated condensed phases and low-density vapor phases. Simulation results indicate that no matter whether there is a substrate in the nucleation process, firstly gaseous atoms gather to form amorphous transitional clusters, and then amorphous transitional clusters gradually transform into ordered graphene crystals, with continuous accumulation of new gaseous atoms and position adjustment of atoms. In the nucleation process, five membered ring structures act as a transitional function. When grown on the substrate with a good geometric match with the honeycomb lattice, such as (111) plane of FCC metals, the graphene island has small structural defects. However, when grown without a substrate or on the substrate with a bad geometric match, such as (100) plane of FCC metals, the graphene island contains many structural defects and grain boundaries, which are not conducive to the preparation of high quality graphene. Compared with the (100) crystal plane of the tetragonal cell, the (110) crystal plane of the rectangular cell is favorable for the preparation of graphene single crystals with less defects. Therefore, the appropriate metal substrate can promote the nucleation process of graphene and reduce the formation of distortions and defects during the nucleation and growth of graphene.

Single crystal preparation and x-ray structure analysis of non-peripherally alkyl-substituted phthalocyanine blends

Single crystals of non-peripherally alkyl-substituted macrocycle molecules, such as octahexylphthalocyanine (C6PcH2), octapentylphthalocyanine (C5PcH2), octahexyltetrabenzotriazaporphyrin (C6TBTAPH2), and their blends were prepared. The crystal structures of C6PcH2 and C5PcH2, which were determined by single-crystal X-ray structure analysis, were identified as monoclinic lattices, while that of C6TBTAPH2 was identified as a triclinic lattice. Despite the similarity between the crystal structures of C6PcH2 and C5PcH2, the single crystals grown from the blended solutions of C6PcH2 and C5PcH2 were based on a triclinic lattice. On the other hand, in the case of the single crystals composed of C6PcH2 and C6TBTAPH2, another type of crystal structure did not appear. The crystal structures of these single crystals are discussed by taking the differences in the alkyl-substituent length and the core structure into consideration.

Simulation and Experimental Studies on Grain Selection Behavior of DD5 Single Crystal Superalloy

Optimization design and simulation of the spiral selector in the process of single crystal preparation were studied. Based on the analysis of simulation and experiment results, the grain structure and orientation in different section height at starter block and spiral part have been discussed. The influence and mechanism of spiral selector parameters on the behavior of the crystal selection were proposed. The design standard of the spiral selector was put forward.

Design and Development of Instrumentations for the Preparation of Platinum Single Crystals for Electrochemistry and Electrocatalysis Research. Part 1: Semi-Automated Crystal Growth

In this contribution, we report on a novel design of semi-automated system for the growth of spherical platinum (Pt) single crystals. The system is based on the flame fusion methodology, where the crystal melting/solidification process is controlled by the vertical movement of a hydrogen–oxygen flame by using an actuator. The paper systematically examines the impact of several process variables on the crystal growth. First, the hydrogen–oxygen flame is optimized through control of the gas flow rate and the mixing ratio to ensure the formation of high-quality platinum single crystals. The procedure of crystal growth is documented in a step-by-step manner, starting with cleaning of the Pt wire, followed by the initial formation of metallic sphere, and ending with repetitive zone refining combined with chemical etching. The equilibrium shape of the platinum single crystals is discussed, and the individual low and high Miller index facets identified and visualized. The critical step in the single-crystal growth, the repetitive zone refining, is semi-automated in order to ensure the highest quality crystals and reproducibility, and to minimize any human error.

Hole Transfer Property at Single Crystal Prepared from Triphenylamine-Derivative Based on Solubility and Supersolubility Curves

In this report, we describe anisotropic hole transport in a triphenylamine-derivative single crystal prepared by a solution method with solubility and supersolubility curves. Triphenylamine derivatives are commonly used as a hole-transport material for organic devices. In the electrophotographic photoconductors, the materials are used in an amorphous form, in which charge carrier mobility is in the order of ~104 cm2V-1s-1. For realizing a further high mobility as an organic semiconductor, preparation of a single crystal seems to be a promissing way. In this study, a single crystal of a trihenylamine derivative (TPA : α-Phenyl-4'-[(4-methoxyphenyl)phenylamino]stilbene) was prepared and its anisotropic hole transport property was measured. Firstly, solubility and supersolubility curves were measured employing a tetrahydrofuran (THF) as a solvent. Based on the results, a single crystal preparation was conducted using 45 wt.% TPA solution with a cooling rate of 0.125 °Ch-1 started from 35°C for 48 h, resulted in a crystal of 8 x 0.8 x 0.4 mm. A polarizing microscope observation demonstrated an extinction angle, which ensures that the TPA single crystal is obtained. Next, current-voltage properties of the TPA single crystal were measured in a vacuum chamber connected to a source meter (Keythley 2612A). For the measurement, A set of Au parallel electrodes with a distance of 20 μm were vacuum deposited on the crystal. From the results, long-axis (direction of 8 mm at TPA single crystal) current is larger than the short-axis (direction of 0.8 mm at TPA single crystal) current, which reveals anisotropic hole transport in the crystal is observed. This can be well explained by a molecular orientation of the crystal structure. Figure 1

Effect of HClO4 Concentration on Oxygen Reduction Reaction Activity at Pt and Pt-Co Alloy Single Crystal Electrodes

Pt-based alloys such as Pt-Fe, Pt-Co and Pt-Ni, have attracted much attention as cathode catalysts with enhanced activities for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs).1 Recently, we have found by use of an electrochemical quartz crystal microbalance (EQCM) and a rotating disk electrode (RDE) that the specific adsorption of perchlorate anion on a Pt-skin/Pt-Co alloy polycrystalline electrode was stronger than that on bulk-Pt, and that the kinetically-controlled current densities jk for the ORR at the Pt-skin/Pt-Co decreased with increasing HClO4 concentration more steeply than that in the case of bulk-Pt, due to the blocking of the active sites by the specifically adsorbed perchlorate anion. 2 In practical PEFCs, Pt-based nanoparticles dispersed on carbon supports are employed in the catalyst layer, and the nanocatalyst surfaces usually consist of low-index crystal facets such as (111) and (100). Recently, we have established a facile method for preparation of Pt-Co alloy single crystals with desired Co contents,3 and have revealed the strong dependence of the ORR activity jk on the Co content at Pt-skin/Pt100-xCox(111) electrodes prepared by annealing under pure H2 atmosphere.4 In the present research, we have evaluated jk at well-defined Pt-skin/Pt-Co alloy single crystal electrodes as a function of HClO4 concertation [HClO4] by using the rotating disk electrode (RDE) method in order to clarify the effect of specific adsorption of perchlorate on the ORR activity. The preparation of Pt-Co alloy single crystal electrodes has been described elsewhere.3 Prior to the electrochemical measurements, well-defined (1 × 1) surfaces of polished crystal electrodes were freshly prepared by heating to 1170 K in H2, and subsequent cooling in H2 for the (111) and (100) planes or 1% CO/He streams for the (110) plane.3 This heat treatment resulted in the formation of a Pt-skin layer on the Pt-Co alloy single crystal surface with the same atomic arrangement as the underlying crystal, confirmed by low energy ion scattering (LEIS) and low energy electron diffraction (LEED).4 Figure 1 shows cyclic voltammograms (CVs) at a Pt-skin/Pt81Co19(111) electrode acquired in various concentrations of HClO4 purged with N2. The ohmic loss was corrected based on impedance measurements. The CVs exhibited characteristic, highly reversible features, i.e., the hydrogen underpotential deposition (HUPD) wave and the so-called butterfly wave, with a broad peak around 0.85 V, in the surface-oxidation region. At 0.05 M ≤ [HClO4] ≤ 0.2 M, no significant changes were observed in the HUPD region. In contrast, with increasing [HClO4], it was found that the double layer currents increased and the surface oxidation wave shifted to higher potentials due to specific adsorption of perchlorate anion, similar to the polycrystalline Pt-Co alloy.2 Figure 2 shows jk values of Pt73Co27(111)-RDEs at 0.9 V vs. RHE in air-saturated HClO4 solutions as a function of [HClO4]. As [HClO4] increased from 0.05 to 0.2 M, the jk values decreased, similar to the case of the polycrystalline Pt-Co alloy.2 The decrease in jk can be ascribed to the blocking of the ORR active sites on the Pt-skin layer by perchlorate anions. However, the jk value in the 0.01 M HClO4 solution was significantly lower than those for other concentrations. The lower jk value in 0.01 M HClO4was presumably due to the low activity of protons, which are consumed in the ORR on the surface. This work was supported by the funds for the “SPer-FC Project’’ of NEDO (Japan) and a Grant-in-Aid No. 25410007 for Scientific Research MEXT of Japan.

Epitaxially Grown Pt and Pt-Ir Thin Films: Effect of the Deposition Conditions on the Electro-Oxidation of Ammonia

Ammonia (NH3) is a highly toxic gas, a major environmental pollutant, and a potential fuel for fuel cells. Thus, the electrooxidation of NH3 has important applications in NH3 safety sensors, NH3 decontamination in wastewater and power production. However, on most electrode materials, NH3 oxidation reaction proceeds with a high overpotential, low current density, and rapid poisoning rate. Better electrocatalysts for this reaction would lower the NH3 detection threshold in sensors, increase the rate of NH3 removal for decontamination, and boost power of NH3 fuel cells. Platinum is the electrocatalyst that shows the highest current density at the lowest overpotential for catalyzing the oxidation of NH3 to N2. The electrooxidation of NH3 on Pt is further complicated by the fact that the reaction rate strongly depends on the metal surface structure. In alkaline medium, the electrooxidation of ammonia on Pt occurs almost exclusively on surface sites with (100) symmetry, especially on wide terraces. Accordingly, the preferred way to study the effect of alloying Pt with other elements would be to rely on a series of mixed Pt-M alloy single crystals with the appropriate (100) surface termination. However, the preparation of single-crystals is difficult. In the case of Pt-Ir, the situation is even more complicated since the Pt-Ir binary phase diagram shows that Pt and Ir are barely miscible at temperature below 1000°C, which could translate into insurmountable technical difficulty in the preparation of Pt-M alloy single crystals. In recent years, Pulsed Laser Deposition (PLD) has emerged as an effective method for preparing thin films with preferential orientation and kinetically stable alloys. In this work, we will study the influence of different deposition parameters (composition, temperature and thickness) on the electro-oxidation of ammonia. To achieve this, a combination of X-ray diffraction (ϴ - 2ϴ scans, rocking curves and pole figures) and atomic force microscopy will be used to get information about the surface organisation and the length of the terraces. Then, electrochemical measurements will be performed to confirm the preferential (100) surface orientation and evaluate the electrochemical performances of the various films for the oxidation of NH3. It will be shown that the current for the electro-oxidation of NH3 varies with the Pt content and the thickness of the film (see Fig. 1). For the thinnest films, the role of Ir atoms in helping the formation of large (100) terraces will be emphasized. Figure 1 Variation of the current density for the electro-oxidation of NH3 with respect to the Pt content. The data were collected from the current at 0.71 V vs RHE during cyclic voltammetry (20 mV.s-1) in 0.1M NaOH + 0.1M NH3. Figure 1

Preparation and characterization of single crystals [Ln(TBPO)4(NO3)2]NTf2 (Ln = Eu, Gd)

Two single crystals [Ln(TBPO)4(NO3)2]NTf2 (Ln=Eu, Gd) were prepared and characterized by element analysis, single crystal X-ray diffraction, PXRD, FT-IR, TGA and fluorescence spectroscopy. The two compounds have similar coordinate structures, in which the central metal ion is coordinated by four TBPO (Tri-n-butylphosphine oxide) molecules and two bidentate nitrates, while NTf2−(bis(trifluoromethylsulfonyl)imide anion) acts as the counter anion. The packing modes of the two crystals are same. The two single crystals are the focus on 8-coordinate tetra-TRPO complexes (TRPO is Trialkyphosphine oxides).

A Screening Approach for the Discovery of Mechanochromic Gold(I) Isocyanide Complexes with Crystal-to-Crystal Phase Transitions.

Mechanoinduced phase transitions of emissive organic crystalline materials have received much attention. Although a variety of such luminescent mechanochromic compounds have been reported, it is challenging to develop mechanochromic compounds with crystal-to-crystal phase transitions in which precise structural information about molecular arrangements can be obtained. Here, we report a screening approach to explore mechanochromic compounds exhibiting a crystal-to-crystal phase transition. We prepared 48 para-substituted (R(1)) phenyl[para-substituted (R(2)) phenyl isocyanide]gold(I) complexes designated R(1)-R(2) (six R(1) and eight R(2) substituents) and then performed three-step screening experiments. The first screening step was selection of emissive complexes under UV light, which gave 37 emissive R(1)-R(2) complexes. The second screening step involved evaluation of the mechanochromic properties by emission spectroscopy. Twenty-eight complexes were found to be mechanochromic. The third screening step involved preparation of single crystals, reprecipitated powders, and ground powders of the 28 mechanochromic R(1)-R(2) complexes. The changes in the powder diffraction patterns of these complexes induced by mechanical stimulation were investigated. Two compounds exhibited a crystal-to-crystal phase transition upon mechanical stimulation, including the previously reported H-H complex. Single crystals of the as-prepared and ground forms of the newly discovered CF3-CN complex were obtained. Density functional theory calculations indicated that the mechanoinduced red-shifted emission of CF3-CN is caused by formation of aurophilic interactions. Comparison of the crystal structures of CF3-CN with those of the other complexes suggests that the weaker intermolecular interactions in the as-prepared form are an important structural factor for the observed mechanoinduced crystal-to-crystal phase transition.

1.8 μm luminescent properties and energy transfer of Yb3+/Tm3+ co-doped α-NaYF4 single crystals

This paper reports on successful preparation of α-NaYF4 single crystals co-doped with ∼1.9 mol% Tm3+ and various concentrations (3.85 mol%, 7.69 mol%, 11.54 mol%, 15.38 mol%) of Yb3+ by using a flux-Bridgman method. The fluorescence decay curve was measured to investigate the luminescent properties of the Yb3+/Tm3+ co-doped α-NaYF4, and the energy transfer process from Yb3+ to Tm3+; the J-O intensity parameters of Tm3+ were further calculated and analyzed according to the absorption spectra. Results show that, an intense 1.8 μm emission was achieved with Yb3+ as sensitizer for Tm3+ in the α-NaYF4 single crystal under the excitation of 980 nm LD (Laser Diode) because of the strong energy transfer from Yb3+ to Tm3+. The maximum emission intensity at 1.8 μm is obtained at about 15.38 mol% doping concentration of Yb3+ when the concentration of Tm3+ ions is fixed at ∼1.90 mol% in the current research. Moreover, the calculated maximum value of emission cross section at 1.8 μm is 1.63 × 10−20 cm2 for 3.85 mol% Yb3+/1.9 mol% Tm3+ sample, and the obtained energy transfer rate (WET) and energy transfer efficiency (η) are 1543 s−1 and 83.8%, respectively. Our analysis of the fluorescence dynamics indicates that electric dipole-dipole interaction is dominant for the energy transfer from Yb3+ ions to Tm3+ ions by using Inokuti-Hirayama’s model.

Preparation of monoclinic Cu2SnS3 single crystal by chemical vapor transport with iodine

Single crystals of monoclinic Cu2SnS3 (CTS) were prepared by chemical vapor transport using iodine as a transport agent. A range of iodine concentrations from 1.5 to 3.0mg/cm3 was employed to determine its effect on crystal growth. The crystals were quenched after vapor transport to prevent the growth of additional, secondary CTS phases. A stoichiometrically balanced CTS product (with a composition ratio of Cu:Sn:S=2.05:1.01:2.94) was achieved using an iodine concentration of 2.0mg/cm3. The results of Raman scattering and X-ray diffraction analyses showed that the samples were CTS crystals with a monoclinic structure. The sample was confirmed to be a single crystal by selected-area electron diffraction patterns, which showed a regular array of spots consistent with monoclinic CTS.

Seeded Growth Route to Noble Calcium Carbonate Nanocrystal.

A solution-phase route has been considered as the most promising route to synthesize noble nanostructures. A majority of their synthesis approaches of calcium carbonate (CaCO3) are based on either using fungi or the CO2 bubbling methods. Here, we approached the preparation of nano-precipitated calcium carbonate single crystal from salmacis sphaeroides in the presence of zwitterionic or cationic biosurfactants without external source of CO2. The calcium carbonate crystals were rhombohedron structure and regularly shaped with side dimension ranging from 33–41 nm. The high degree of morphological control of CaCO3 nanocrystals suggested that surfactants are capable of strongly interacting with the CaCO3 surface and control the nucleation and growth direction of calcium carbonate nanocrystals. Finally, the mechanism of formation of nanocrystals in light of proposed routes was also discussed.

ChemInform Abstract: Review on Nanomaterials Synthesized by Vapor Transport Method: Growth and Their Related Applications

AbstractReview: 88 refs.

Structural and crystal chemical properties of alkali rare-earth double phosphates

When appropriately activated, alkali rare-earth double phosphates of the form: M3RE(PO4)2 (where M denotes an alkali metal and RE represents either a rare-earth element or Y or Sc) are of interest for use as inorganic scintillators for radiation detection at relatively long optical emission wavelengths. These compounds exhibit layered crystal structures whose symmetry properties depend on the relative sizes of the rare earth and alkali-metal cations. Single-crystal X-ray and powder neutron diffraction methods were used here to refine the structures of the series of rare-earth double phosphate compounds: K3RE(PO4)2 with RE = Lu, Yb, Er, Ho, Dy, Gd, Nd, Ce, plus Y and Sc – as well as the compounds: A3Lu(PO4)2, with A = Rb, and Cs. The double phosphate K3Lu(PO4)2 was reported and structurally refined previously, and it exhibited two lower-temperature phases. The compound K3Yb(PO4)2 reported here also exhibits a new second phase that occurs at T = 120 °C with a transformation to hexagonal P-3 space group symmetry and a Yb-ion coordination number reduction from seven to six. This latter result was confirmed using EXAFS. Comprehensive structural data and structural systematics are reported here for a number of alkali rare-earth double phosphates. Additionally, single-crystal growth methods for the preparation of large single crystals of these compounds are described, and the thermal expansion properties of the present series of alkali rare-earth double phosphates, as determined by both X-ray and neutron diffraction methods, are presented. These data represent a structural and thermal characteristics basis for continuing research on the use of alkali rare-earth double phosphates as scintillators for radiation detection – as well as for future studies of the fundamental phase properties of these compounds at elevated pressures.

Combustion Characteristic in Growth Chamber for Preparation of Single Crystal with Hydro-Oxygen Flame Fusion Method

Combustion characteristic in growth chamber for preparation of single crystal with hydrooxygen flame fusion method was investigated. The results show that along the centerline of growth chamber a peak temperature 3504.3 K could be reached when the flow rates of oxygen and hydrogen were 6 L/min and 20 L/min respectively. With the increasing hydrogen flow rate, the temperature of the center and the diameter of the central flame increased gradually in the chamber. With the increasing oxygen flow rate, the position of the peak temperature gradually moved down, which downward moved 5 mm when the central oxygen flow rate increased for 1 L/min, while the average temperature rose ca 230℃at a distance 110 mm to the nozzle. The diameter of hydrogen distribution circle had little effect on the center and radial temperature distributions, the central oxygen impact and the ignition position of the flame. As a result, the optimal position for single crystal growth could be easily acquired for the preset flow rates of the two gases and vice versa.