Defects of different sizes in large paratellurite single crystals

Paratellurite single crystals have good acoustooptical properties that are important for various devices, such as deflectors, modulators, and tunable noncollinear filters. Paratellurite single crystals of up to 80 mm in diameter and 100 mm in height were grown using the Czochralski method from ultrapure melts. Optical anomalies in the grown crystals—gas bubbles, striations, impurity inclusions with nearby stresses, and regions with high dislocation densities—were studied with chemical, X-ray, and optical methods.     

On the nature of growth hillocks on sodium chlorate crystals

Optical examination of as-grown {100} surfaces of sodium chlorate crystals grown from aqueous solution revealed the presence of elliptical growth hillocks. The hillocks were present on both enantiomorphous forms and originated from dislocations, inclusions, and microcrystals attached to the growing surface. The value of the surface entropy factor equal to 4.55 at 313 K suggests that crystals grow via/or with the participation of dislocation mechanism, and the hillocks are dislocation growth centers. Compound mechanism controlled growth of some crystals because edge nucleation and dislocation centers operated simultaneously on the same surfaces.     

On the Growth Morphology of K2Cr2O7 (KBC) Crystals

The morphology of potassium dichromate (KBC) crystals grown under different conditions by solvent evaporation method is investigated. Observations of the examination of asgrown surfaces and inclusions, and of the realtion between dislocations and inclusions are presented. The results indicate that the change in the morphology of KBC crystals can be associated with the dislocation structure in the crystal.     

Propagation behavior of threading dislocations during physical vapor transport growth of silicon carbide (SiC) single crystals

The dislocation formation and propagation processes in physical vapor transport (PVT) grown 4H silicon carbide (4H–SiC) single crystals have been investigated using defect selective etching and transmission electron microscopy (TEM). It was found that while the growth initiation process generally increased the density of threading dislocations in the grown crystal, for certain areas of the crystal, threading dislocations were terminated at the growth initiation. Foreign polytype inclusions also introduced a high density of dislocations at the polytype boundary. In the polytype-transformed areas of the crystal, almost no medium size hexagonal etch pits due to threading screw dislocations were observed, indicating that the foreign polytype inclusions had ceased the propagation of threading screw dislocations. Based on these results, we argued the formation and propagation of the threading dislocations in PVT grown SiC crystals, and proposed the dislocation conversion process as a plausible cause of the density reduction of threading dislocations during the PVT growth of SiC single crystals.     

CZ法生长参数对TeO2晶体质量的影响

本文主要讨论CZ法生长TeO2晶体中温度梯度、拉速、转速等工艺参数对晶体质量的影响,分析了晶体开裂、包裹物等宏观缺陷以及位错等微观缺陷的形成机理.从晶体形态、包裹体和位错密度变化等方面探讨了晶体生长参数与晶体缺陷之间的内在关系.     

Spontaneous polarization of triglycine selenate and triglycine fluoberyllate

Spontaneous polarization of Triglycine Selenate and Triglycine Fluoberyllate was investigated with crystals produced under various growing conditions. Spontaneous polarization of TGSe crystals grown at the Curie temperature is of the greatest value. The higher the supersaturation of the solution from which TGSe crystals were grown, the greater the spontaneous polarization. TGFB crystals grown at high temperatures are of greater value of spontaneous polarization than those grown at low temperatures.     

Etching Figures in Neodymium Gallate and Yttrium Aluminate Crystals

The dislocations existing in single crystals of neodymium gallate and yttrium aluminate grown by the Czochralski technique have been studied by means of etch pits. The data concerning their solubility in cases of different directions of a face orientation, various treatment temperatures and several enchant types are reported. The investigation of etch pits in the twinned YAlO₃ and NdGaO₃ crystals showed that twins are formed during a growth process. In the [110]‐pulled NdGaO₃ crystals the discrepancy between the twin and matrix parts of a crystal is accommodated by the dislocation congestion and the dislocation low‐angle boundaries whereas in [010]‐pulled YAlO₃ crystals the microcracks perform this function.     

Crystal growth of potassium perchlorate in gelatin gels

The suitability of gelatin gel for the growth of good quality single crystals of potassium perchlorate has been investigated. Growth in a more rigid and simple apparatus has been accomplished and described here. The grown crystals were identified by X-ray analysis. A study of the relation of crystal morphology to concentration of feed solutions and growth temperature has also been made. Studies made on chemical etching of the cleavages have revealed that the crystals are relatively perfect. At times, large liquid inclusions which introduce stresses in the crystals are responsible for a large dislocation concentration.     

Internal defect structures of olivine crystals

Defect structures of olivine crystals (Czochralski grown forsterite, flux grown forsterite and natural olivine) were studied by means of chemical etching method, X-ray topography and light scattering tomography. Two etchants were used for revealing the dislocation sites; one is the etchant described by WEGNER , CHRISTIE , another is that by DESAI , JOHN . It was found that great care was needed in identifying dislocation sites using these etchants since they attack the impurity sites as well as dislocation sites. The results obtained are as follows; (1) The Czochralski grown forsterite and flux grown forsterite were free from sub-boundaries and the dislocation density was smaller than that of a natural olivine. There existed many sub-boundaries in the natural olivine. (2) X-ray topographic study showed that (i) the dislocation lines of the Czochralski grown forsterite consisted mainly of straight segments nearly parallel to the low index direction, whereas (ii) no dislocation lines corresponding to the etch pits were observed in the flux grown forsterite. (3) The study by light scattering tomography showed that there existed various types of scattering centers in these olivine crystals and that the density and shape were different among them.     

Elektronenmikroskopische Untersuchungen zur Rißausbreitung bei der Zugverformung gewalzter Molybdän-Einkristalle

The effect of dislocation structure on mechanical properties, crack propagation and fracture was investigated in molybdenum single crystals predeformed by rolling to produce a homogeneously distributed dislocation structure or a cell structure. The rolled crystals were notched and deformed by tension at various temperatures (493, 293 and 193 K). It is shown, that the crystals with cell structure ((111) [112 ] orientation) have the higher strength, but the crystals with homogeneous structure ((001) [110] orientation) are more ductile. In cell structure cracks propagate catastrophically without pronounced necking. The homogeneous structure becomes unstable during tensile loading above the transition temperature, but crack propagation occurs slowly involving complete necking of the crystal. At low temperatures (193 K) cleavage fracture on {100} planes takes place both in the crystals with homogeneous and cell structure.     

Röntgentopographische Untersuchung von KDP-Kristallen

The dislocation configuration arising in KDP crystals grown from the solution has been studied by X-ray diffraction topography method (Lang-method). The space orientation of dislocations and their Burgersvektor directions are determinated. The dislocations density did not exceed 10³ cm⁻², and there are areas which were free form dislocations. The sources of dislocations were classified as inclusions of mother liquor and foreign particles respectively.     

Glow Curves of Thermally Pretreated KCl:Mn2+ Crystals

Thermoluminescence studies of KCl crystals doped with 0.5 mole% of Manganese both in “as grown” state and after quenching them from various elevated temperatures indicate that the position of the glow peaks is found to depend upon the state of dispersion of impurity. In quenched crystals two additional peaks one around 130 and other around 215°C are observed. Dipoles near dislocations are suggested to be responsible for 130°C peak and 215°C peak to a complex formed by the associated of one or more Mn²⁺ ions with a single vacancy or an aggregate of vacancies, the complex being situation in the dislocation region.     

Evolution of dislocation structures in a crystal under deformation

The system of equations describing the dislocation kinetics which provides plastic deformation in fcc and bcc metal crystals over a wide range of temperatures and stresses has been studied. The general types of solution and the two-parameter diagram of solution bifurcation are obtained as functions of stresses and temperatures. The diagrams of various types of solution are compared with the diagram of experimentally observed dislocation structures.     

The morphology of succinic acid crystals: The role of solvent interaction

Succinic acid crystals grown from aqueous solutions are platy with a (100) basal plane and side faces (111) and (011), while crystals grown from iso-propanol are needle-like with (100) and (010) planes. These habits are not predicted from PBC analyses. In this study, the role of solvent interaction is related to habit controlling factors in the screw dislocation mechanism. The solvent interaction with various faces of succinic acid crystals was determined with the aid of molecular mechanics calculations. The observed habits from water and from iso-propanol could be explained satisfactorily in a semi-quantitative way.     

Properties of Doped GaSb Single Crystals Grown by the Czochralski Method

The specific electrical properties and average dislocation density of GaSb crystals are shown and discussed regarding various elements presented as dopant. The single crystals were grown by the Czochralski method without encapsulant in a flowing atmosphere of molecular hydrogen, on the one hand, and of atomic hydrogen, on the other hand. The results are summarized in the Table II.     

Analysis of synthetic diamond single crystals by X-ray topography and double-crystal diffractometry

Structural features of diamond single crystals synthesized under high pressure and homoepitaxial films grown by chemical vapor deposition (CVD) have been analyzed by double-crystal X-ray diffractometry and topography. The conditions of a diffraction analysis of diamond crystals using Ge monochromators have been optimized. The main structural defects (dislocations, stacking faults, growth striations, second-phase inclusions, etc.) formed during crystal growth have been revealed. The nitrogen concentration in high-pressure/high-temperature (HPHT) diamond substrates is estimated based on X-ray diffraction data. The formation of dislocation bundles at the film-substrate interface in the epitaxial structures has been revealed by plane-wave topography; these dislocations are likely due to the relaxation of elastic macroscopic stresses caused by the lattice mismatch between the substrate and film. The critical thicknesses of plastic relaxation onset in CVD diamond films are calculated. The experimental techniques for studying the real diamond structure in optimizing crystal-growth technology are proven to be highly efficient.     

Atomic force microscopy studies on liquid inclusions and induced defects of cadmium mercury thiocyanate crystal

Liquid inclusions and various defects accordingly induced on a nonlinear optical material of CMTC crystal were investigated by atomic force microscopy. Liquid inclusions are chiefly caused by formation of macrosteps, which result from impurity‐induced inhibiting of step growth and meeting of step trains advancing along different directions. Liquid inclusions induce generation of dislocations and even cracks within the crystal by three‐dimensional nucleation growth. Liquid inclusions also provide screw dislocation growth sources, leading to formation of spiral hillock trains with ridged tails. Etching experiments reveal circular hollow cores, indicative of screw dislocation growth, and negative crystals resulting from further crystallization in the liquid inclusions. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The influences of supersaturation on LPE growth of GaN single crystals using the Na flux method

The dependency of LPE growth rate and dislocation density on supersaturation in the growth of GaN single crystals in the Na flux was investigated. When the growth rate was low during the growth of GaN at a small value of supersaturation, the dislocation density was much lower compared with that of a substrate grown by the Metal Organic Chemical Vapor Deposition method (MOCVD). In contrast, when the growth rate of GaN was high at a large value of supersaturation, the crystal was hopper including a large number of dislocations. The relationship between the growth conditions and the crystal color in GaN single crystals grown in Na flux was also investigated. When at 800 °C the nitrogen concentration in Na–Ga melt was low, the grown crystals were always tinted black. When the nitrogen concentration at 850 °C was high, transparent crystals could be grown.     

Melt growth and post‐grown annealing of semiinsulating (CdZn)Te by vertical gradient freeze method

We present results of development of CdZnTe semi‐insulating crystals prepared by Vertical Gradient Freeze method in a 4‐zone furnace. We applied the way of growth of the crystal from the top when the first crystallization seed is created on the surface of the melt. The typical height of the crystals is 5 cm. Resistivity and photoconductivity profiles measured along the growth axis by contactless method are compared and their mutual correlation is explained based on a model of relative shift of the Fermi level and the midgap level present in the material. The influence of the Fermi level on electron trapping and recombination is summarized. We present here results of a two‐step annealing method aimed at reduction of Te inclusions while keeping the resistivity high. We employed CdTe:Cl VGF grown samples to eliminate Te inclusions observed in as grown crystals by two‐step post grown annealing in Cd and Te atmosphere and present a model of the processes leading to high resistivity material after annealing.     

声光晶体TeO2的生长及缺陷研究

本文研究了直接ＴeO２晶体中的主要晶体缺陷形成机理,讨论分析了Ｔ eO2单晶生长的工艺参数对晶体缺陷的影响,结果表明：晶体裂缝的主要与温度梯度有关,温度梯度大于２０－２５℃/cm及出现界面翻转时,易造成晶全的开裂,位错密度增加,晶体中的包裹体主要为气态包裹全,它的形成主要与籽晶的转速和晶体的提拉速率有关,转速１５－１８r/min,拉速０.55mm/h,固液界面微凹,可以减少晶体中的气态包裹体,晶体台阶由晶体生长过程中温度和生长速度的引起伏引起,当台阶间距较宽时,易形成包裹体。