The influence of temperature gradient and lowering speed on the melt-solid interface shape of GaxIn1-xSb alloy crystals grown by vertical Bridgman technique

Radially homogeneous bulk alloys of GaxIn1-xSb in the range 0.7 < x < 0.8, have been grown by vertical Bridgman technique. The factors affecting the interface shape during the growth were optimised to achieve zero convexity. From a series of experiments, a critical ratio of the temperature gradient (G) of the furnace at the melting point of the melt composition to the ampoule lowering speed (v) was deduced for attaining the planarity of the melt-solid interface. The studies carried out on directional solidification of Ga0.77In0.23Sb mixed crystals employing planar melt-solid interface exhibited superior quality than those with nonplanar interfaces. The solutions to certain problems encountered during the synthesis and growth of the compound were discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

Nanoindentation of Bridgman YBCO samples

In this study, the mechanical properties of YBa2Cu3O7−x, obtained by the Bridgman technique, were examined using a Berkovich tip indenter on the basal plane (0 0 1). Intrinsic hardness was measured by nanoindentation tests and corrected using the Nix and Gao model for this material. Furthermore, Vickers hardness tests were performed, in order to determine the possible size effect on these measurements. The results showed an underestimation of the hardness value when the tests were performed with large loads. Moreover, the elastic modulus of the Bridgman samples was 128 ± 5 GPa. Different residual imprints were visualised by atomic force microscopy and a focused ion beam, in order to observe superficial and internal fracturing. Mechanical properties presented a considerable reduction at the interface. This effect could be attributed to internal stress generated during the texturing process. In order to corroborate this hypothesis, an observation using transmission electron microscopy was performed.

Growth, magnetotransport, and magnetic properties of ferromagnetic (In,Mn)Sb crystals

In1−xMnxSb crystals are grown with different Mn doping concentrations (x = 0.006, 0.01, 0.02, and 0.04) beyond the equilibrium solubility limit by the horizontal Bridgman technique. Structural, magnetic, and magnetotransport properties of the grown crystals are studied in the temperature range 1.4–300 K. Negative magnetoresistance and anomalous Hall effect are observed below 10 K. The anomalous Hall coefficient is found to be negative. The temperature dependence of the magnetization measurement shows a magnetic ordering below 10 K, which could arise from InMnSb alloy formation. Also, the saturation in magnetization observed even at room temperature suggests the existence of ferromagnetic MnSb clusters in the crystals, which has been verified by scanning electron microscopy studies. The carrier concentration increases with Mn doping, and this results in a decrease of resistivity. The carrier concentration and mobility at room temperature for the doped crystals are ∼ 2×1019 cm−3 and ∼ 200 cm2/V s, respectively. The observed anomalous Hall effect suggests the carrier mediated ferromagnetism below 10 K in In1−xMnxSb crystals.

Orientation Selection and Microstructural Evolution in Directionally Solidified Tb0.3Dy0.7Fe1.95

Tb0.3Dy0.7Fe1.95 alloy was directionally solidified by using a modified Bridgman technique at a wide range of growth rates of 5 to 100 cm/h. The directionally grown samples exhibited plane front solidification morphology up to a growth rate of 90 cm/h. Typical island banding feature was observed closer to the chilled end, which eventually gave rise to irregular peritectic coupled growth (PCG). The PCG gained prominence with an increase in the growth rate. The texture study revealed formation of strong aOE (c) 311 > texture in a lower growth rate regime, aOE (c) 110 > and ``rotated aOE (c) 110 > aEuroe in an intermediate growth regime, and aOE (c) 112 > in a higher growth rate regime. In-depth analysis of the atomic configuration of a solid-liquid interface revealed that the growth texture is influenced by the kinetics of atomic attachment to the solid-liquid interface, which is intimately related to a planar packing fraction and an atomic stacking sequence of the interfacial plane. The mechanism proposed in this article is novel and will be useful in addressing the orientation selection mechanism of topologically closed packed intermetallic systems. The samples grown at a higher growth rate exhibit larger magnetostriction (lambda) and d lambda/dH owing to the absence of pro-peritectic (Tb,Dy)Fe-3 and formation of aOE (c) 112 > texture, which lies closer to the easy magnetization direction (EMD).

Space growth studies of Ce-doped Bi12SiO20 single crystal

Ce-doped Bi12SiO20 (BSO) single crystal was grown on board of the Chinese Spacecraft-Shenzhou No. 3. A cylindrical crystal, 10 mm in diameter and 40 mm in length, was obtained. The morphology of crystals is significantly different for ground- and space-grown portions. The space- and ground-grown crystals have been characterized by Cc concentration distribution, X-ray rocking curve absorption spectrum and micro-Raman spectrum. The results show that the quality of Ce-doped BSO crystal grown in space is more homogeneous and more perfect than that of ground grown one. (C) 2004 Published by Elsevier B.V.

Buoyancy driven flow and its stability in a horizontal rectangular channel with an arbitrary oriented transversal magnetic field

An MHD flow is considered which is relevant to horizontal Bridgman technique for crystal growth from a melt. In the unidirectional parallel flow approximation an analytical solution is found accounting for the finite rectangular cross section of the channel in the case of a vertical magnetic field. Numerical pseudo-spectral solutions are used in the cases of arbitrary magnetic field and gravity vector orientations. The vertical magnetic field (parallel to the gravity) is found to be he most effective to damp the flow, however, complicated flow profiles with "overvelocities" in the comers are typical in the case of a finite cross-section channel. The temperature distribution is shown to be dependent on the flow profile. The linear stability of the flow is investigated by use of the Chebyshev pseudospectral method. For the case of an infinite width channel the transversal rolls instability is investigated, and for the finite cross-section channel the longitudinal rolls instability is considered. The critical Gr number values are computed in the dependence of the Ha number and the wave number or the aspect ratio in the case of finite section.

Desenvolvimento de um dispositivo para obtenção de monocristais de ligas à base de cobre

This paper describes the drawing, construction and optimization of a device, which can be used to obtain single crystals of different metallic materials with melting point from 550 to 1050°C. Components of ease obtaining and of low cost were used. The device was based on the modified Bridgman technique and it was used to obtain single crystals of copper-based alloys. The temperature axial profiles and a difference less then 1% in the temperature between the wall and the center of the ceramic tube in the critical region for obtaining single crystals of good quality indicated that the oven presents a good thermal stability. Single crystals of CuZnAl and CuAlAg alloys of good quality were growth and characterized using optical microscopy and Laüe X-ray back reflection.