Growth Sector Boundaries Research Articles

Time evolution and spatial distribution of temperature in YBCO bulk superconductor after pulse field magnetizing

The time evolutions of temperature rise ΔT(t) after pulse field magnetizing have been measured on the surface of a cryo-cooled YBaCuO bulk superconductor. The temperature rise ΔT increases with increasing pulse field strength, and a quite large temperature rise (ΔTmax ∼ 18.8 K) is observed just before the trapped magnetic flux reaches the central region of the bulk. The epoxy resin, impregnated and coated to the bulk crystal for mechanical reinforcement, prevents the heat exhaust towards the cold stage of the refrigerator and it needs much time to recover its initial temperature. The spatial distribution of ΔT(t) has indicated that the magnetic fluxes tend to enter into the bulk, avoiding the 4-fold growth sector boundaries of the bulk crystal.

Elastic deformation in a crystal plate where lattice–parameter mismatch is present between adjacent growth sectors. II. Measurement of lattice tilts by synchrotron X–ray reticulography

Synchrotron X–ray reticulography measures lattice–plane orientation variations point by point on the crystal with microradian resolution capability. A fine–scale X–ray–absorbing mesh placed close to the crystal in the back–reflected diffracted beam of ‘white’ X–rays splits the beam into an array of microbeams whose direction differences are measured from the mesh–bar shadow shifts that result from controlled changes of the distance between the mesh and the recording high–resolution photographic plate. In the present work, lattice tilts were measured on either side of a growth–sector boundary outcropping at the surface of a single–crystal synthetic diamond cut and polished parallel to (110) in which the displacements and strains due to lattice–parameter mismatch at coherent growth–sector boundaries have been analysed in part I. Attention was concentrated on a crystallographically well–defined planar segment of a boundary separating two sectors, each of uniform, but significantly differing, concentration of substitutional nitrogen impurity, and for which the anisotropic elasticity theory of part I provided quantitative relations between the lattice–parameter relative difference, Δa/ā, and the lattice tilts due to coherency strains at the boundary. This enabled a novel method for determining Δa/ā to be realized, using reticulographic measurements of tilts of near–surface lattice planes alone. The paper explains the reticulographic technique fully. Factors affecting the quality and reliability of reticulographic records are examined in detail. For the growth sectors concerned, the reticulographic measurement Δa/ā = (1.10 ± 0.10) × 10−5 is in accord with an earlier finding by synchrotron X–ray double–crystal diffractometry, slightly revised as recommended in part I, Δa/ā = (1.20 ± 0.07) × 10−5. The closeness of the findings by two quite different methods confirms the conclusion from X–ray topography that the growth–sector boundary was free from misfit dislocations compensating the lattice–parameter mismatch. On mismatch boundaries in crystals too highly absorbing for transmission X–ray topography, such comparisons of reticulographic and diffractometric measurements would reveal information otherwise inaccessible by non–destructive methods.

Synchrotron white beam topography characterization of physical vapor transport grown AlN and ammonothermal GaN

Structural defects in AlN single crystals grown by the sublimation method and GaN single crystals grown by the ammonothermal method are characterized by synchrotron white-beam X-ray topography in conjunction with optical microscopy. AlN platelets are either of (1 1 2 ̄ 0) or (0 0 0 1) type depending on the growth conditions. Dislocation densities of the order of 10 3 cm −2 or lower are observed in some crystals. X-ray topographs reveal the presence of growth sector boundaries, inclusions, and growth dislocations that indicate slight impurity contamination. The 2H crystal structure of GaN single crystals obtained by the ammonothermal method was verified by Laue X-ray pattern analysis. GaN crystals grown are of the order of 1 mm in size and are either (0 0 0 1) platelets or [0 0 0 1] prismatic needles. Generally, prismatic needles are characterized by lower degree of mosaicity than (0 0 0 1) platelets.

Growth-Sector Boundaries and Growth-Rate Dispersion in Potassium Alum Crystals

Crystals of potassium alum, pure and slightly doped with Cr 3+ , were grown from aqueous solution by slow temperature lowering. In addition, short re-dissolution periods were introduced in order to provoke growth defects and changes of growth rates. Crystal slices of about 1 mm thickness were studied by conventional LANG X-ray diffraction topography using MoKa radiation. For Cr-doped crystals, boundaries between {100}, {100} and {111} growth sectors appear by pronounced dynamical X-ray topographic contrast similar to that of stacking faults. Re-dissolution experiments provoke the formation of inclusions on {100} faces, followed by an increase of the { 100} growth rate by the factor of about six, relative to the neighboured {111} faces. X-ray topographs show that this-increase is correlated with the formation of dislocations, which interestingly have pure-edge character. During further growth these dislocations penetrate the {100}-{111} growth sector boundary and vanish from the {100} face, which slows down and finally adopts its former growth rate before re-dissolution.

Fluid inclusions in sphalerite as negative crystals: a case study

The crystal morphology of vacuoles of fluid inclusions in some transparent, low-iron and relatively low-temperature sphalerites from the vein and replacement Pb-Zn ore deposits of the Madan ore district, Bulgaria, was studied both by optical microscopy in oriented thin sections and by SEM on open cleavage surfaces. The vacuoles represent negative crystals bounded by faces of d {110}, o {111} and - o {111} forms together with small faces of a {100}, e {210}, n {211}, p {221}, - n {211} and - p {221} forms. Their corners and edges are rounded. The primary inclusions, formed mainly at 200–220 °C, have an isometric, elongated, tubular, spindle-like or acute-angled habit depending on their position and the influence of the growth defects (growth zones, subgrain and sector boundaries, twin planes, etc .). The secondary fluid inclusions, healing fractures in sphalerite crystals mainly at 160–185 °C, are strongly controlled by the thickness and local configuration of the crack surfaces. They are flat, irregular or isometric in shape. It is suggested that the fluid inclusions in the low-T sphalerite usually preserve their initial high-energy and non-equilibrium crystal morphology formed during periods of rapid growth.

The perfection and defect structure of organic hourglass inclusion K 2SO 4 crystals

Hourglass inclusion crystals of K 2SO 4 were grown from aqueous solutions containing the dye acid fuchsin, and studied by synchrotron white-beam X-ray topography and reciprocal space mapping. Both self-nucleated and larger, seeded dye-included crystals were prepared, as well as comparable undoped crystals. While the dye modified the crystals’ habit strongly, X-ray topographs showed it had no influence on their dislocation configurations, which were typical for solution-grown crystals. No kinematical contrast arising from the presence of the dye was observed that indicated dye-induced strain in the crystal lattice. Growth sector boundaries were visible in the dyed crystals but not in undoped crystals, implying there was a slightly higher lattice mismatch across growth sector boundaries in the dye-included crystals. Reciprocal space maps of small areas on an hourglass inclusion crystal within either a dye-included growth sector or an undoped growth sector showed single peaks with the same perfect crystal rocking curve width and no dilatation or tilt of the host lattice resulting from the dye's presence. These results showed hourglass inclusion crystals can be grown in which the presence of the dye disturbs the crystalline structure of the host salt minimally, and that hourglass inclusions have the nature of a solid solution.

Growth defects in BiB 3O 6 crystals observed with white-beam synchrotron topography

The growth defects in BiB 3O 6 (BIBO) crystals have been investigated by white-beam synchrotron radiation topography for the first time. It is found that inclusions, dislocations and growth sector boundaries are the primary growth defects nearby the seed. The area away from the seed is nearly free of defects. Based on the experimental observations, the formation mechanism of brown region in BIBO crystals is discussed. Twins and growth sector boundarie exist in the brown region, which is the key reason resulting in brown presentation. The approaches to reduce and eliminate the defects are presented.

Synchrotron radiation topographic characterization of L-arginine phosphate monohydrate crystals

The growth defects in solution grown L-arginine phosphate monohydrate (LAP) organic crystals were investigated by white-beam synchrotron radiation topography. The crystals were cut into slices in different directions. The transmission topographies showed the dislocations, growth striations, growth sector boundaries and inclusions in both (100) slice and (001) slice with different reflection. We also presented the contrast of microbe, which is a severe problem in LAP crystal growth. The topography with 015 reflection showed the dislocations originated from the surface of the seed and following the (001) and (100) direction, and the Burgers vectors of those dislocations were determined. The dynamic images of growth sector boundaries were also showed clearly.

Growth-dependent properties of KTP crystals and PPKTP structures

Growth of optically uniform and single ferroelectric domain KTP crystals is of prime importance for frequency-conversion applications. In the course of KTP growth from pure self-fluxes the flux becomes enriched in potassium causing a gradual increase of potassium content in the crystal as well. We have shown that such an effect can be well characterized by a corresponding increase in the Curie temperature of the crystal. Establishment of the potassium concentration gradients is followed by charge separation and production of a built-in electric field, which can be enhanced or diminished also by the incorporation of charge-compensating residual impurities. The magnitude of the built-in electric field is directly proportional to the projection of the potassium concentration gradient on the crystal's Z-axis, and it defines the domain direction in immersion seeded or different configurations of the top-seeded growth of KTP crystals. Detailed investigation of the domain formation mechanisms has allowed us to suggest a number of ways of growing single domain crystals, such as top-seeded growth with pulling in the Z-direction. Pulling in the X-direction is shown to yield predominantly bi-domain crystals. The formation of bi-domains and complex domain structures along the growth sector boundaries is explained in terms of edge-like and apex-like growth perturbations, respectively, which are due to temperature fluctuations at the growth interface. The knowledge of parameters influencing the domain formation mechanisms has allowed us to develop a technique for obtaining as-grown periodic domain structures necessary for large aperture (high-power) frequency conversion applications. © 2001 Kluwer Academic Publishers

X-ray Topographic Characterization of L-Arginine Phosphate Monohydrate Crystals

L-arginine phosphate monohydrate (LAP) organic crystals were investigated by X-ray Lang topography. Selected topographs of nearly perfect seeded grown and self-nucleated crystals show that typical defects inside are grown-in and post-growth dislocations, growth sector boundaries, and microbes, while their features are presented and discussed. No structural defects associated to the presence of step bunching on the (100) surface of the crystal have been observed by X-ray topography.

Growth and sector zoning in a beryl crystal

The structural defects and minor element concentrations of a beryl crystal from Brumado (Bahia, Brazil) were studied by X-ray diffraction topography and electron probe microanalysis. Examination showed that crystal growth was divided into two main stages, with significant differences with regard to defect density and variations in minor element concentrations, particularly Mg and Na. In the first growth stage, compositional variations and low defect density were observed; in the second stage, there was a decrease in impurity content and a sharp rise in defect density. Reconstruction of the growth history allowed the growth-sector boundaries to be located and related to compositional variations. In the first growth stage, minor element concentrations varied sharply when crossing the boundaries between the pinacoidal-pyramidal and pyramidal-prismatic growth sectors, whereas they decreased smoothly in the prismatic sector. They were therefore interpreted to be sector and chemical zonings respectively. Only chemical zoning was detected in the second stage of crystallisation.

Transmission double–crystal synchrotron studies of synthetic diamond using the Haruta stereo–pairs technique

The Haruta method of obtaining a stereoscopic effect by a small rotation about the diffraction vector was used for the first time in the case of synchrotron X–ray double–crystal topography. Double–crystal experiments were performed on a 1.5 x 4 x 4mm 3 slab cut from a cuboctahedral synthetic diamond in the arrangement where the asymmetric 220 diamond reflection was matched by the 331 reflection from a silicon monochromator selecting 1.0 A radiation. The double–crystal topographs provided intense contrast for dislocations, stacking faults, growth–sector boundaries and other defects, often accompanied by distinct interference fringes. The images were strongly angle dependent and appropriate Haruta pairs were matched from series taken at positions on the rocking curve separated by small increments. The pairs exhibited a good stereoscopic effect for most of the defects, and also for the cases of many interference fringes. The stereoscopic effects were also compared with those obtained in single–crystal Haruta pairs in exactly the same geometry. It was found that some fringes, associated with some growth–sector boundaries and stacking faults, did not, however, produce a good stereoscopic effect, but the fringes appeared visible on the exit surface. These various features were confirmed by simulation of the stereoscopic effects in computer–calculated images of dislocations and stacking faults.

Growth, Defects and Electrooptic Properties of RbTiOAsO4 Crystal

RbTiOAsO4 (RTA) crystals of high optical quality were grown with flux method. The defects of RTA crystals are mainly growth striations, growth sector boundaries and sometimes ferroelectric domains. The refractive indices and electrooptic coefficients were measured together with dielectric constants, ionic conductivity and direct current resistivities. It is shown that RbTiOAsO4 is not only as good a nonlinear optical crystal as KTiOPO4 but also a superior electrooptic crystal.

Growth defects in flux grown RbTiOAsO 4 crystals observed with white-beam synchrotron radiation topography

The growth defects in flux grown RbTiOAsO 4 crystal have been investigated by white-beam synchrotron radiation topography. It is found that growth sector boundaries are the primary growth defects and they show strong X-ray kinematical contrast in the topograph. All the dislocations are growth induced and appear only in the near capping region. The area away from the capping region is nearly dislocation free. Growth bands show weak contrast in the X-ray topograph, which implies that the impurity contents are relatively low in various growth sectors and each growth sector is uniform in composition.

Characterization of protein and virus crystals by quasi-planar wave X-ray topography: a comparison between crystals grown in solution and in agarose gel

Quasi-planar wave reflection profile and X-ray topography studies have been done to characterize the mosaicity of solution- and gel-grown crystals of three proteins, turkey egg-white (TEW) lysozyme, thaumatin, and a bacterial aspartyl-tRNA synthetase (AspRS) as well as of one virus, tomato bushy stunt virus (TBSV). These materials are representative of a large range of molecular weight, overall particle shapes, crystals habits, packings, and solvent contents. Measurements of the full-width at half-maximum (FWHM) of reflections show that these different crystals have all a weak mosaicity. Topographs display the same features as those of the well-studied hen egg-white (HEW) lysozyme crystals: misorientation generated at the seed level for TEW lysozyme or thaumatin crystals and/or strains at growth sector boundaries for AspRS crystals. No growth defects are evidenced for TBSV crystals. For the study of crystals diffracting at lower resolution (AspRS and virus), a less absorbant sample holder, which facilitates crystal positioning in the X-ray beam, has been developed. The results obtained for solution- and gel-grown crystals do not show important differences. However, for TEW lysozyme and thaumatin crystals, one notices a larger dispersion of results in the solution case and an overall tendency for improved reproducibility of quality for gel-grown crystals.

Synchrotron radiation topographic observation of KTiOPO4crystals under an electric field

In situwhite-beam synchrotron radiation topographic observations under an electric field have been made on the KTiOPO4(KTP) family of crystals. The investigation shows a strong enhancement of diffracted intensity forhklreflections (l ≠ 0) and topographic contrast in the form of fine striations when the external electric field is parallel to the polar axis. Several kinds of doped and undoped samples with various grown-in defects, such as domain boundaries, growth striations, growth-sector boundaries, dislocations,etc., have been studied in detail. The results suggest that these defects have very little effect on the field-induced striations. It is believed that the movement of K^+ ions driven by the electric field leads to a local accumulation of charges and a lattice distortion. The strongly anisotropic conductivity is a governing factor in the explanation of the field-related phenomena in this kind of quasi-one-dimensional conductor.

Optical microscopic, synchrotron X-ray topographic and reticulographic study of homoepitaxial CVD diamond

Surface topography and crystal-lattice perfection of homoepitaxial layers deposited by microwave plasma CVD on (0 0 1) and near-(0 0 1) facets polished on HPHT synthetic diamond are described. Optical micrographic techniques included birefringence, Nomarski and 2-beam interference. The synchrotron X-ray experiments comprised Laue topography plus a recently developed sensitive misorientation-measuring technique, reticulography. Two special circumstances enhanced information yield from the experiments. First, the substrate crystal was unusually strain-free and had a very low dislocation content. Second, epilayer growth had taken place in two stages, depositing thicknesses of 10 μm and 30–34 μm, respectively. This double deposition complicated the observations, but added features of scientific and practical interest. Epilayer cracking finally present had occurred almost entirely before the second growth stage. With assistance from quantitative data provided by reticulography, the X-ray diffraction properties of the substrate and epilayers are analysed. Lattice misorientations on the untreated lower surface of the substrate were only ∼1 arcsec except close to growth-sector boundaries and dislocation outcrops. The final epilayer growth surface above areas where cracking in the first epilayer was absent or sparse exhibited near-perfect-crystal diffraction behaviour.

An investigation of growth-induced defects in crystals of potassium hydrogen phthalate

Abstract The growth-induced defect structure of solution-grown crystals of potassium hydrogen phthalate (KAP) has been investigated using synchrotron X-ray diffraction topography. The majority of the crystals examined contained very low defect densities and levels of strain. Dislocation densities typically varied between about 5 and 15cm−2. The strain associated with growth sector boundaries was so low as to render them invisible in most topographic images. All crystals exhibited substantial sectorial variation in the extent of solvent inclusion, with growth sectors at one end of the crystal polar axis incorporating substantially higher levels than the other end. The relationship between the asymmetry of solvent incorporation and that of the growth-induced surface topology of KAP crystals has been examined using ex-situ atomic force microscopy. The dislocation density in most of the crystals studied also showed a pronounced sectorial dependence. A detailed characterization of growth dislocations was carried out. Dislocations with Burgers vectors [001], [100], 〈101〉 and 〈110〉 were observed with [001] being dominant. A substantial proportion of the observed dislocations occurred in pairs which adopted a v-shaped configuration. In some cases, the different line directions of the pair arose from different Burgers vectors for each dislocation of the pair. The divergence of the dislocations in other instances is attributed to nucleation of the pair on a growth sector boundary with each dislocation of the pair lying in a different growth sector and therefore adopting a different line direction.

An investigation of growth-induced defects in crystals of potassium hydrogen phthalate

Abstract The growth-induced defect structure of solution-grown crystals of potassium hydrogen phthalate (KAP) has been investigated using synchrotron X-ray diffraction topography. The majority of the crystals examined contained very low defect densities and levels of strain. Dislocation densities typically varied between about 5 and 15cm−2. The strain associated with growth sector boundaries was so low as to render them invisible in most topographic images. All crystals exhibited substantial sectorial variation in the extent of solvent inclusion, with growth sectors at one end of the crystal polar axis incorporating substantially higher levels than the other end. The relationship between the asymmetry of solvent incorporation and that of the growth-induced surface topology of KAP crystals has been examined using ex-situ atomic force microscopy. The dislocation density in most of the crystals studied also showed a pronounced sectorial dependence. A detailed characterization of growth dislocations was carri...

The relationship between crystal growth and defectstructure: a study of potassium hydrogen phthalate using x-raytopography and atomic force microscopy

An investigation of the defect structure of crystals of potassium hydrogen phthalate (KAP) and its relationship to the crystallization behaviour has been carried out using x-ray diffraction topography and atomic force microscopy (AFM). Crystals of KAP grown from aqueous solution were found to exhibit very low defect densities in the range 5 to 15 cm-2 and remarkably low levels of strain. The character and distribution of the dominant growth dislocation types were determined using x-ray topography. The most significant features of the dislocation structure were a tendency for certain dislocation types to nucleate in pairs and at growth sector boundaries. X-ray topography revealed sectorial variations in solvent inclusions and the complementary use of AFM has shown the relationship of this to growth spiral anisotropy on the (010) face of KAP crystals. Changes in KAP crystal morphology have been observed which result from extreme variations in dislocation density, leading to either spiral growth or, in the case of dislocation-free growth sectors, a two-dimensional nucleation mechanism. The bending of dislocations from one growth sector to another and the tendency of dislocations in this material to nucleate in pairs are discussed in the context of size-dependent crystal growth rates.