Growth Of Large Single Crystals Research Articles

Top-seeded growth of superconducting (Ba1−ϰKϰ)BiO3 crystals by an electrochemical method

A method is described for the growth of large single crystals of cubic BKBO. The improved technique uses top-seeded growth from Na-free compositions through use of a BKBO reference electrode. By careful control of over-potential it is possible to control the K content (ϰ) and homogeneity in the crystals. For ϰ = 0.38 the highest T c was obtained (32 K) with a sharp transition ( ΔT = 1 K). Details are reported for the crystal growth process and the superconducting properties.

Mathematical Model for the Simulation of Crystallization of CdTe in a vertical Bridgman Furnace.

ABSTRACTTemperature measurements in a crystal growth ampoule of CdTe (Cadmium Telluride) are very difficult. Mathematical simulation is a very powerful tool to predict the behavior and temperature distribution during crystal growth. We applied this technique to the bulk growth of large single crystals of CdTe. The simulation revealed that for CdTe, it is possible to create a convex interface shape during growth, necessary for single crystal growth. The controlling parameter is the temperature profile along the ampoule. The temperature gradient is rather meaningless, as we can show with our simulations.We will present some crystals grown under good and bad thermal conditions.

Computer simulation of CdTe crystal growth and application

In a step towards intelligent material processing, we studied the effect of the temperature distribution in the growth ampoule on the crystallization process. We constructed a mathematical model to calculate the temperature distribution in the sample, using the temperature profile in the furnace. In the experimental part, this profile was accurately imposed by our modified vertical Bridgman furnace with 12 independent zones. This equipment was applied to pure CdTe, which is known to be a difficult material with which to achieve large single crystal growth. After optimization of the temperature profile and the other growth parameter, we grew several large single crystals.

Single crystals of a chimeric T7/T3 RNA polymerase with T3 promoter specificity

Two RNA polymerases homologous to bacteriophage T7 RNA polymerase - bacteriophage Sp6 and T3 RNA polymerases - were screened for crystallization under conditions identical or similar to those reported for the growth of large single crystals of T7 RNA polymerase. A number of mutant T7 RNAPs were also screened under these conditions, as were three chimeric RNA polymerases consisting of T7 RNAP N-terminal and T3 RNAP C-terminal sequences. One chimeric polymerase and two mutant polymerases crystallized readily under T7 RNAP crystallization conditions. The chimeric polymerase crystallized in a space group different from T7 RNA polymerase: orthorhombic with unit cell parameters a = 75A˚, b = 98A˚, c = 159A˚; space group P2 12 1 2 1 and 4 molecules per unit cell. This chimeric enzyme exhibits T3 promoter specificity and will make it possible to investigate how structural differences between the T3 and T7 RNA polymerase promoter recognition domains determine their different promoter specificities.

Structural and defect characterization of CuInS 2 single crystals grown under elevated pressures

By using an argon overpressure, large CuInS 2 single crystals were produced. Upon modification of the temperature gradient over the melt a change of structural features was induced. Low temperature gradients resulted in the growth of large single crystals, whereas for increased temperature gradients sheet-like material was prepared. The lamellar material cleaved along the (112) planes as revealed by reflection high-energy electron diffraction, and the appearance of Kikuchi lines indicates good crystallinity. Within the limits of X-ray diffraction the material was shown to be single-phase CuInS 2. IR measurements were employed for comparison of materials with different structural properties. Possible origins for the new lamellar structure are discussed. Additional information obtained by a new angle-resolved reflection spectroscopy on the defects in CuInS 2 single crystals is presented. The method permits the room temperature detection of small variations of the complex dielectric function ϵ. The variation of ϵ = ϵ 1 + ige 2 position in the band gap. The defect levels determined from this method are compared with photoluminescence and transmission spectroscopy results.

Growth of large single crystals of meta-nitroaniline

Large single crystals of metal-nitroaniline (m-NA) have been grown from solution by the lowering-temperature method. A small seed was used in the solution and a large single crystal with high optical quality, measuring 30×40×50 mm ( a× b× c) was g The growth conditions and results of this crystal are described.

Phase Relations in the Cu‐In‐S System and Growth of Large CuInS2 Single Crystals

The phase relations in the metal portion of the Cu‐In‐S system have been investigated by differential thermal analysis (DTA) and x‐ray diffraction (XRD). The pseudobinary reveals a region of liquid immiscibility indicating the extension of the two liquid region from the Cu‐S binary to the In‐S binary. This two liquid region is intersected by two eutectics which originate at the quasibinary system. In addition, the growth of large single crystals of have been facilitated by growth under elevated argon pressures. Growth in large temperature gradients results in a lamellar type phase, which shows good optical and electrical properties. Data from XRD, reflection high energy electron diffraction, and rocking curves are presented on the structural and morphological properties, and photoluminescence was used for a defect characterization of this material.

Growth of large single crystals of YBa 2Cu 3O 6+x with various values of x

Large single crystals of YBa 2Cu 3O 6+x for inelastic neutron scattering studies have been grown. Relationship between the growth conditions and the amount of the flux inclusion, which is important for the oxygen number control, is discussed.

Single crystals of a chimeric T7/T3 RNA polymerase with T3 promoter specificity and a nonprocessive T7 RNAP mutant.

Two RNA polymerases homologous to bacteriophage T7 RNA polymerase, bacteriophage Sp6 and T3 RNA polymerases, were screened for crystallization under conditions identical or similar to those reported for the growth of large single crystals of T7 RNA polymerase (Sousa, R., Rose, J. P., Chung, Y. J., Lafer, E. M., and Wang, B.-C. (1989) Proteins 5, 266; Sousa, R., Lafer, E. M., and Wang, B.-C. (1990) J. Crystal Growth, in press; Sousa, R., and Lafer, E. M. (1990) Methods 1, in press). A number of mutant T7 RNAPs were also screened under these conditions as were three chimeric RNA polymerases consisting of T7 RNAP N-terminal and T3 RNAP C-terminal sequences. One chimeric polymerase and two mutant polymerases crystallized readily under T7 RNAP crystallization conditions. The chimeric polymerase crystallized in a space group different from T7 RNA polymerase: orthorombic with unit cell parameters a = 75 A, b = 98 A, c = 159 A; space group P2(1)2(1)2(1) and 4 molecules/unit cell. This chimeric enzyme exhibits T3 promoter specificity and will make it possible to investigate how structural differences between the T3 and T7 RNA polymerase promoter recognition domains determine their different promoter specificities. One of the mutant polymerases successfully crystallized was an enzyme which can carry out promoter recognition and abortive transcription but cannot carry out processive transcription. Its structure may provide information on the nature of the conformational changes undergone by T7 RNAP in the abortive-processive switch. Crystals of the second mutant T7 RNA polymerase were unsuitable for x-ray analysis.

Crystallization and preliminary X-ray investigation of lipoxygenase 1 from soybeans.

Soybean lipoxygenase 1 has been crystallized by the vapor diffusion method in 8-10% polyethylene glycol (average Mr 3400), 0.2 M sodium acetate buffer, pH 5.2-5.6, at a protein concentration of 6-12 mg/ml. Microseeding was employed to obtain growth of large single crystals. The crystals, which diffract to at least 2.2-A spacings, are monoclinic and of space group P2(1). Cell constants are: a = 95.4, b = 94.2, and c = 50.4 A and beta = 91.4 degrees. The calculated value of Vm (2.41 A3/Da) is consistent with the probable presence of one molecule of lipoxygenase/crystallographic asymmetric unit (Z = 2).

The growth of large single crystals

It is possible to obtain a wide range of nicely formed crystals utilizing solution methods and commonly available materials and apparatus.

Large single crystals of mercuric iodide from the vapour phase; preparation of a space experiment

Recently, the vapour growth of large single crystals has been recognized as an attractive new field in materials research under microgravity conditions and mercuric iodide as a model substance for the growth experiments in space. Presently we are involved in the development of a sophisticated growth facility for the European Space Agency in which long-term (up to 6 months) vapour growth (computer controlled) experiments can be performed under microgravity conditions (telescience). There are several prerequisites in the development of this facility, which have been identified as separate technical or scientific tasks of the project and are discussed in this paper: (1) high resolution in situ measurements of the growth rate of the crystals as a function of crystallographic orientation, (2) crystal surface temperature measurements for evaluation of the actual supersaturation, which is the driving force for the growth, (3) a cooling system capable adjusting the cooled area to the increasing crystal size (in order to avoid thermal stresses in the crystal). For automatic control of the growth, the dependence of the growth rate on supersaturation for various starting materials (doping, nonstoichiometry) has to be known in advance; for this purpose the transport rate will be measured in a separate precursor space experiment (DCMF).

The Protein Crystallization Facility (PCF) for EURECA

Research on the structure of molecules by X-ray diffraction analysis requires large single crystals. However, the dynamic behavior of proteins caused by their high molecular weight prevents the growth of large single crystals if this process is disturbed by thermal convection. For example, protein single crystals grown under terrestrial (1 g) conditions are limited to dimensions in the order of 0.1 mm, whereas the size of crystals, grown under (quasi) space conditions has been 5 times larger (pilot experiment CRYOSTAT, Spacelab). Under EURECA conditions (e.g. no μg disturbances), the result in regularity of crystal growth and size is expected to be much better. In this paper an overview is given of the protein crystallization facility which includes Experiment-, Service- and Secondary Cooling Module, and its interfaces to the EURECA Carrier. At the end, there will be presented a short mission profile concerning cooling-, power- and data exchange requirements.

Structural studies on improved crystals of the photosystem I reaction centre from Phormidium laminosum

Improved crystallization methods led to the growth of large single crystals of the photosystem I reaction centre isolated from the thermophilic cyanobacterium Phormidium laminosum. Although the crystals exhibited a high degree of mosaicity, some preliminary X-ray diffraction studies were performed. The highest order reflections found correspond to interplanar spacings of approx. 0.8 nm. In conjunction with electron microscopy of thin three-dimensional crystals, a triclinic or monoclinic crystal system with unit cell dimensions 30 × 18 × 18 nm was assigned. In addition, our data suggest the presence of four trimeric complexes per unit cell, which may be organised as two face-to-face pairs.

Growth of large single crystals of oxide superconductor YBa 2Cu 3O X

Single crystals of YBa 2Cu 3O X having a large aspect ratio (thickness/diameter) have successfully been prepared using a CuO or a BaO CuO flux method. The crystals show a sharp superconducting transition above 90 K. Crystal growth proceeds in the condition that solid and liquid coexist and a peritectic reaction among them plays an important role. In this investigation, an experiment was held at various growth-temperatures and composition of flux for the purpose of obtaining crystals of higher quality.

Equilibrium pressures of oxygen above YBa2Cu3O7±x up to 2,000 bar

The interaction of oxygen with the high-temperature superconducting oxides is very important because several phenomena that influence the superconducting properties, such as the orthorhombic to tetragonal phase transformation, are dependent on the oxygen stoichiometry. In spite of this, many of the basic thermodynamic pressure data remain unpublished. The existing information indicates that the decomposition of YBa2Cu3O7–x starts at T = 400 °C at Po2 = 1 bar (ref. 1), and that the compound melts incongruently2. Pressure data and corresponding melting points are therefore needed, to ascertain if it is possible to change the phase diagram at higher oxygen pressures so that the compound melts congruently. If this were feasible, then the growth of large single crystals from a stoichiometric melt could be possible. Here we present the equilibrium oxygen pressure curve for the YBa2Cu3O7±x decomposition (P–T phase diagram) up to 2,200 bar and 1,200 °C. To construct the three-dimensional P–T–x phase diagram of the pseudo-binary system O2–YBa2Cu3O7±x, we have also developed methods for measuring the T–x diagram at high pressure, and we present the first data at 10 bar oxygen pressure.

Containerless growth of large single crystals of TiAl

Titanium aluminides based upon TiAl are potential high temperature materials having low density, high modulus, good oxidation resistance, and do not disorder with increasing temperature. Because of the lack of ambient temperature ductility their utilization is limited. Some investigations have been carried out to further understand the mechanical behavior of these intermetallics. Other research indicates that the mechanical properties of single crystal compounds, as well as alloyed single crystal compounds can have superior properties. In order to begin studies of the basic mechanical properties of these aluminides, an investigation to grow relatively large single crystals of TiAl was undertaken. Mechanical property investigation of the pure compound as well as alloyed single crystal material are objectives of the program. Alloying has the potential or improving the properties of this L1/sub o/ intermetallic.

Melt-processible rare earth-Ba-Cu-O superconductors based on molten Ba-Cu oxides

Ba-Cu oxides with certain compositions were found to be meltable or partly meltable at a relatively low temperature of 950 °C. High-quality, dense, and void-free high-temperature superconductors based on rare earth(RE)-Ba-Cu oxides of the form REBa2Cu3O6.5+x have been made by reactions between molten Ba-Cu oxides and solid RE-containing materials at the same temperature. This has allowed superconductive components to be made in a wide variety of shapes. This melt process will significantly alter oxide superconductor preparation procedures, and will allow growth of large single crystals aiding in the understanding of the mechanism of superconductivity and in the search for superconductivity at even higher transition temperatures.

Growth of large single crystals from aqueous solution: A review

The growth of large single crystals from aqueous solution remains an important challenge. The physical mechanisms involved in such growth and the problems entailed for successful growth processes are reviewed. Approaches to these problems are discussed with emphasis on recent research progress. Coverage includes solution preparation, crystallizer technology, bulk supersaturation control, and measures to avoid solution inclusion flawing. Although current production goals will probably not be met in the near future, fundamental advances are being made in understanding the general process of crystallization from solution.

Growth of large single crystals of KTiOPO 4 (KTP) from high-temperature solution using heat pipe based furnace system

A process is reported for crystal growth of KTiOPO 4 from its solution in K 6P 4O 13 using a seeded, slow cooling technique. A new furnace system is reported for use in the process, its key feature being a heat pipe providing for a high degree of spatial temperature uniformity throughout the growth solution. Initial surface dissolution appears necessary to achieve flaw-free growth immediately off a seed. Avoidance of solution inclusion flawing in advanced stages of growth requires a crystal orientation configuration and rotation pattern that does not give rise to stable regions of uncirculating growth solution. Through the process, 10-day growth runs routinely produce flaw-free crystals large enough to yield plates 10 × 10 × 7 mm 3 oriented in the optimal direction for second harmonic generation having properties measured to be at least as good as KTiOPO 4 grown by other methods.