Twinning in hydrothermally grown synthetic quartz as revealed by etch structures

Etch structures obtained by HF etching on habit and cleaved rhombohedral surfaces of synthetic quartz grown by hydrothermal crystallization technique, indicative of twinning in them are described, illustrated and discussed. The twin traces appear in the form of lines of dis-continuity in [1121] and [1211] directions. Etch pits within the parallelogram-shaped bound areas are oppositely oriented with respect to those on the rhombohedral surface of the main crystal. The form of twinning observed is found to be of parallel lattice type and the surface within and outside the bound areas are coplanar in most of the cases. The rhombohedral faces of the twinned crystals are found to be geometrically related to each other as if one part is derived from the other by a rotation of 180° about [1210] direction. Discontinuation in the crystal lattice along the twin trace is evidenced by obstructions in the normal development of an etch pit. Deep penetration of twin traces and parallelogram-shaped regions, enclosing etch pits of opposite orientation (twinned areas), well within the crystal structure is demonstrated by comparison of etch patterns on matched rhombohedral cleavages and the results on their successive etching. The type of twinning displayed by the crystals is discussed in the light of models suggested. Causes for the generation of twinning in synthetic quartz are explained to lie in the availability of twinned nuclei in the seed plates used for hydrothermal crystallization of quartz.     

Revelation of microtwinning in hydrothermally grown synthetic quartz by growth structures

Growth structuress on prism surfaces of synthetic quartz grown by hydrothermal crystallization technique, indicative of microtwinning in them are described, illustrated and discussed. The microtwins are revealed by the misorientation of the growth structures, and it is observed that microtwinning is manifested in different forms. Twinned domains appear in the form of strictly oriented, square striated (stepped) structures with inclined surfaces, seemingly overlapping square striated structures, square and irregular regions demarcated by black line-like boundaries, patch-like structures enveloping irregularily bound domains, tongue-like terraces bordered by irregular line of discontinuity of varying height and the regions with both differently shaped as differently oriented growth structures. From the orientations of the square shaped growth structures, it is shown that crystals consist of domains which are in twin relationship to the main crystal. Twins by rotation around an axis perpendicular to (10ī0) with rotation angles of 60°, 90°, and 180° have been observed. Critical examination of some twin boundaries delineated by black line-like matter, with the application of multiple beam interferometry and FECO reveal that the black boundary is a ridge (line-elevation). The line elevation along such a twin boundary is explained to be as a result of preferential adsorption of impurity atoms along the trace of the boundary. It is further observed that discontinuity in crystalline structure along the twin boundary leads to growth forms with distorted morphology thus establishing strong dependence of growth forms on the underlying crystalline structure. Causes for generation of the microtwins (twinning on a microscale) in synthetic quartz are discussed.     

The electrolytical coloration of synthetic quartz crystals with induced growth striations

Electrolytical coloration of quartz crystals with induced smoky quartz striations has been investigated, and compared with the arrangement of smoky quartz stripes after X-irradiation. Investigations have been made on z-, s-, −x- and +x-regions of the crystal after application of an electrolytical current in z-direction.     

Nature of radiation defects in synthetic quartz according to the small-angle neutron scattering data

The supraatomic structure of single crystals of synthetic quartz in the initial state with a dislocation density of 570 cm^?2 and after irradiation in the VVR-M reactor at the Petersburg Nuclear Physics Institute with fast neutrons having the energy E _n > 1 MeV in the range of fluences F _n = 7.7 × 10¹⁷ ?2.1 × 10²⁰ neutrons/cm² has been studied by small-angle scattering of thermal neutrons. It is established that fast neutrons form point, linear, and volume lattice defects throughout the entire sample volume. Large-volume structures (nuclei of the amorphous phase) in quartz, reaching ～100 nm in size, occupy a small total volume (～1.5%) even at the maximum fluence 2.1 × 10²⁰ neutrons/cm². The majority of damage is related to the point defects with the radius of gyration of 1–2 nm and linear defects, which give comparable contributions up to several percent.     

Inclined Dislocations in Synthetic Calcite Crystals

A large number of perfect (100) cleavages were obtained by cleaving the laboratory grown synthetic calcite crystals. By etching such cleavages in 20% ammonium chloride solution, it is established that the pits indicate the sites of dislocations in the crystals. This is further confirmed by comparing the etch patterns on matched cleavage surfaces. Eccentricity of the pits has been attributed to the inclined nature of dislocations. Existence of parallel dislocations seems to be due to the purity of the crystal. These observations are verified by comparing etch patterns produced on opposite faces of a thin flake (0.048 mm thick) and also by successive etching and polishing a cleavage surface. It is conjectured that curl-bottomed pits nucleate at the sites of screw dislocations in the crystal. The implications are discussed.     

Dislocations in BZS and PMN pyrochlores

The dislocations observed in Bi_3/2ZnSb_3/2O₇ (BZS) and Pb_1.83Mg_0.29Nb_1.71O_6.39 (PMN) pyrochlores are described. An attempt is made to determine the Burgers vectors.     

Dislocations (Solitons) in anharmonic crystals

Static dislocations (solitons) in an anharmonic lattice are studied within the framework of the Frenkel-Kontorova model. The dislocation-induced fields corresponding to the displacement vector and the stress tensor are calculated, and their properties are analyzed. The process of soliton nucleation is discussed in terms of the kinetics of the excited phonon subsystem of a loaded crystal. The expressions describing the nucleation time and the force and the energy conditions of a dislocation (soliton) nucleation are derived.     

Precipitation-induced Dislocations in Crystals of NaCl:Ni

Using the decoration technique, the dislocation structure has been observed in regions localized near precipitates in nickel-doped NaCl crystals. The results are interpreted in terms of the stress-operated mechanism for the generation of prismatic dislocations by the precipitates. Normally only two of twelve possible slip directions operate for 〈110〉 rods. This is accounted for in terms of the climb and disappearance of dislocation loops corresponding to the other directions. {100} plates produce loops spreading along for 〈110〉 directions.     

Dislocations and grain boundaries in semiconducting rubrene single-crystals

Assessing the fundamental limits of the charge carrier mobilities in organic semiconductors is important for the development of organic electronics. Although devices such as organic field effect transistors (OFETs), organic thin film transistors (OTFTs) and organic light emitting diodes (OLEDs) are already used in commercial applications, a complete understanding of the ultimate limitations of performance and stability in these devices is still lacking at this time. Crucial to the determination of electronic properties in organic semiconductors is the ability to grow ultra-pure, fully ordered molecular crystals for measurements of intrinsic charge transport. Likewise, sensitive tools are needed to evaluate crystalline quality. We present a high-resolution X-ray diffraction and X-ray topography analysis of single-crystals of rubrene that are of the quality being reported to show mobilities as high as amorphous silicon. We show that dislocations and grain boundaries, which may limit charge transfer, are prominent in these crystals.     

X-Ray Studies of Dislocations in Crystals Deformed by Bending

In the present work the results obtained by means of X-ray and etching methods in determination of dislocation density in the case of germanium single crystals plastically deformed by bending around various crystallographic directions have been compared. They prove that the method of counting the etch pits gives the underrated values of the dislocation density when it is of the order 10⁶ cm⁻². The best agreement between the results obtained by means of X-ray method and by chemical etching is observed for bending around the direction [111] and for etching of the faces of type (111).     

Dislocations in silicon observed by high-voltage,high-resolution electron microscopy

Dislocations in deformed silicon crystals have been studied by high-resolution electron microscopy with the axial illumination along the [110] direction using a 1 MV electron microscope. Extended 60 dislocations, Z-shape faulted dipoles and stacking fault tetrahedra were observed in atomic level. The results demonstrated the potentiality of highvoltage, high-resolution electron microscopy for the study of atomic configurations of structural defects.     

Anomalously Large Burgers Vectors of Screw Dislocations in Gallium Nitride Nanowires

Crystallography Reports - The results of structural studies of GaN nanowires containing screw dislocations are presented. It is found that the length of the Burgers vector of dislocations may reach...     

Burgers Vectors of Dislocations in Creep-deformed Fe3Si Single Crystals

In creep-deformed Fe₃Si single crystals the Burgers vectors of the dislocations were examined by transmission electron microscopy. The Burgers vector in a sample deformed under conditions of 60 MPa and 575–600 °C was of the type 1/2 〈110〉, whereas 〈111〉 superlattice dislocations were not found. 1/2 〈110〉 is the shortest translation distance in the D0₃ superlattice structure of Fe₃Si.     

Dislocations of salol crystals grown by the Czochralski method

Crystals of salol were grown by the Czochralski method in three different pulling directions to examine the crystallographic orientation effect of the seed. They were characterized by the etch pit method and X-ray projection topography. It was found that the dislocation density was 2 × 10³−1 × 10⁴/cm² and that the configuration of dislocations was straight. The running directions of dislocations strongly depend on the pulling directions; i.e., [11 0] and [1 10] for the crystal grown in [100] axis, [11 0], [1 10] and [110] for the crystal pulled along [112] axis and [010] for [010] axis crystal.     

Estimation of Core Energy of Dislocations from Etching Data

From data on the activation energy of dissolution at a surface and at a dislocation for the {100} planes of MgO crystals the dislocation core energy is estimated employing Schaarwächter's theory of etch pit formation.     

Electric twinning in quartz by temperature gradient

This paper presents a new method for obtaining electric twins in quartz crystal: thermal treatment in a temperature gradient at about 500 °C, that means under phase transition point. + 5X quartz crystal plates for resonators were used; a temperature gradient of 15–25 °C was applied for 4–5 hours along the Y axis (the place length). For + 5X resonators, the diminution of the resonant frequency and the increase of the inductance were plotted as a function of the level of twinning.     

Growth flawing and strain in hydrothermal quartz

With the aid of optical methods (including interphako microscopy) combined with chemical analysis at selected microareas (X-ray microprobe analyser) it is shown that some macro-defects arise during the growth of quartz single crystals due to the incorporation of foreign particles which are gathered in groups. Frequently, the strain in such crystals is inherited from the seeds. Therefore, the emphasis is laid on the optical investigation of strain in quartz.