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.     

Electrical Processes Occurring at the Moment of Cleaving NaCl Crystals

The electrical processes occurring on cleaving tempered NaCl crystals have been studied by decoration methods on the scale of electron microscopy. The decorating agent, gold, was evaporated at the moment of performing the cleavage. The obtained decoration pictures differed from those described in the literature. Features similar to the propagation of waves were observed. They begin on cleavage steps and are mostly parallel to 〈100〉. On interaction of the “waves” with the steps or with other “waves” there arise black “threads” distinguished, the same as the wave boundaries, owing to a very high contrast on account of the higher density of decorating particles. The waves and threads are interpreted as microbreakdowns, which have also a two-stage character - stages of wave and thread formation, propagate along definite crystallographic directions, and occur at the boundary of strained sites. The charge sign of the waves is determined from the degree of coalescence of decorating gold particles. The detected waves reflect the occurrence of specific polarization states in local sites of the surface. These states are induced by local electric fields of a very high intensity occurring on cleaving the crystals. These polarization states disappear in 10-15 s after the cleavage is made due to neutralization of the charges. Analogy is drawn between polarization structures in form of waves and stable linear polarization bridges occurring in crystals between oppositely charged point defects and their assemblies.     

Dendritic Growth of Potassium Dihydrogen Phosphate Crystals in Silica Gels

Dendritic growth of potassium dihydrogen phosphate (KDP) crystals in silica gels at room temperature is reported. Branching along directions perpendicular to the arms and dendrites growing in mutually perpendicular 〈100〉 and 〈010〉 directions are illustrated. Initial stages and surface of a dendrite are illustrated and described. Also explained are the crystallites growing on the dendrite which finally lead to the formation of platelets.     

Deformation and microhardness studies on KClO4 single crystals

The deformation characteristics of KClO₄ single crystals have been studied by the methods of static and dynamic indentation on (001) plane. The cracks produced by the dynamic indentation have been interpreted in terms of slip-twin interactions. Also, the load dependence of Vickers microhardness and its anisotropy in this crystal are reported. The observed hardness anisotropy has been used to confirm the indices of the slip system 〈101〉 〈111〉 operative in this crystal at ordinary temperatures.     

Crystal growth and dislocation structure of gallium antimonide

Single crystals of GaSb have been grown by the Czochralski method under reducing conditions. Crystals were grown in the 〈100〉, 〈111〉, and 〈112〉 directions. The 〈111〉 growth direction was found to be the most suitable for the successful and reliable crystal growth. Dislocation densities in 〈111〉 oriented crystals were examined by chemical etching. The etch pits density in these crystals didn't exceed the value of 1 × 10² cm⁻².     

Evaporation Model of NaCl Cleavage Faces around Edge Dislocations in Vacuum

It is shown in the present paper that the evaporation of edge dislocations in the form of circular steps takes place in NaCl crystals by the evaporation of these steps in a high vacuum and in a temperature region of 350–500°C. The distances of steps are regular. This regularity is explained by means of a suggested model. This model explains also the change in the evaporation rate depending upon the density of dislocations. This explanation is based on the existence of an effective charge at the emergence point of the edge dislocations a/2 〈110〉. {110} with the surface planes {100}. This charge interacts with another one formed on the faults of steps. As a result of this interaction a modulation is observed of the formation of a new step in the emergence point. This means that the same is observed in the case of step distances too.     

Morphology and orientation relations of BaCl2 precipitates in NaCl single crystals

In the present paper morphology and orientation relations of BaCl₂ precipitates in NaCl single crystals are described. It is shown that BaCl₂ precipitates of large dimensions are formed at the dislocations of a/2〈110〉{100}, the dislocation lines of which are oriented in the directions 〈210〉.     

Structural Defects in Type I Diamonds

Natural gem diamonds of Type I single crystals were observed with an ultra high voltage transmission electron microscope in order to characterize structural defects such as dislocation, dislocation loops, and platelets. The results of analyses indicated that edge dislocations with Burgers vector 1/2 [011 1] and 60° dislocations which were inclined at an angle of 60° to 〈011〉 directions were present in the diamonds. Dislocation loops were concluded to be in interstitical character. It was speculated that an impurity associated with the platelets was silicon and dislocation loops were formed by dislocation motion.     

Controlled synthesis of Cu2O cubic and octahedral nano‐ and microcrystals

Cubic and octahedral Cu₂O nano‐ and microcrystals were selectively synthesized via a simple wet chemical reduction route at room temperature, with CuCl₂ and NaOH as starting reactants, and ascorbic acid or hydrazine hydrate as the reducer. Hydrazine hydrate could be preferentially adsorbed on different crystal faces of Cu₂O, affecting the growth rate along the 〈100〉 to that along the 〈111〉 direction, which resulted in the formation of octahedral Cu₂O crystals. When ascorbic acid was used as the reducer, the growth rate along the 〈100〉 to that along the 〈111〉 direction was different, which resulted in the formation of cubic Cu₂O crystals. The size of cubic and octahedral Cu₂O crystals could be varied by adjusting the molar ratio of OH^– to Cu²⁺. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the incorporation mechanism and distribution mode of impurities in potassium acid phthalate crystals grown from aqueous solutions

Mechanism of impurity structure formation in crystals grown from aqueous solutions has been studied on the example of potassium acid phtalate (abbreviated hereafter as KAP) single crystals. Gold decoration technique at an electronmicroscopic scale has been applied to the study of the distribution of uncontrolled impurities on KAP cleavage face (010) after 10, 20 and 30 days of growth, taking into consideration different growth rates in 〈001〉 and 〈001 〈 directions. A technique for visualization of impurities in water, based on the adsorption of these impurities by the surface of amorphous film of nitrocellulose (parlodion) and the vacuum decoration with gold of these impurities, has been developed. Differences in the impurity structure of KAP regions located in 〈001〉 and 〈001〉 directions from the seed have been established. In 〈001〉 direction after 20 days of growth impurity assemblies 0.1—0.4 μm in size are revealed, and in 〈001〉 direction heterogeneous impurity structure is revealed only after 30 days of growth. The real (impurity) structure of KAP outside impurity assemblies is quite homogeneous and is the same throughout the whole crystal volume, the impurities incorporating mainly into complex active centres. From comparison of the changes in time of the impurity structure of water used for crystallization solutions and the impurity structure of KAP crystals a conclusion is made that the impurity structure of crystals is “programmed” in the impurity structure of crystallization solutions which regularly changes with time, i. e. impurities from different kinds of assemblies which are selectively adsorbed by the growing crystal faces. The role of the adjacent to the growing face interfacial layers which control the growth rate and have a complex impurity structure is stressed.     

Long-Term Changes in Mechanical and Electrical Characteristics of CdTe Crystals after Their Exposure to a Weak Pulsed Magnetic Field

Long-term changes in mechanical and electrical properties of p-type CdTe single crystals have been revealed after their exposure to a weak pulsed magnetic field (B = 1 T, ν = 12 Hz, t_exp = 10 min). A nonmonotonic increase in the hardness of crystals (presence of two peaks) and a nonmonotonic decrease in their specific dark conductivity (three peaks) have been observed. The peaks of changes in mechanical and electrical properties correlate on the time scale. It is shown that the intensity of observed effects depends on the crystal orientation with respect to the direction of magnetic induction vector B. In particular, the observed changes in properties for B || 〈111〉 are twice as large as those for B || 〈110〉. Possible mechanisms of the observed effect are discussed.     

Radial and axial impurity distribution in high-purity germanium crystals

To grow high purity germanium (HPGe) crystals in an underground environment for ultra-low background experiments is being studied. In the present work, HPGe crystals along 〈100〉 direction have been grown by the Czochralski method. In order to investigate the distribution of the impurities as a function of length for a grown crystal, i.e. the axial direction, we fabricated a system to measure the resistivity along the axial direction at both room temperature and liquid nitrogen temperature. The distribution of the impurities along the radial direction was measured with a Hall Effect System. The results show that the carrier concentration in some crystals grown in a hydrogen atmosphere has an impurity level of about 10¹⁰/cm³, which meets the requirements of detector-grade crystals.     

Oriented inclusions in single crystals of potassium dihydrogen phosphate

Different forms of oriented inclusions in single crystals of potassium dihydrogen phosphate (KDP) grown by gel method and from aqueous solutions are reported. Small rod like chain and channel types of liquid inclusions are illustrated. These inclusions are oriented along 〈001〉, 〈011〉 and 〈010〉 directions and are attributed to mother liquor trapped in the body of the crystal during growth.     

Effect of different barium concentrations in KCl crystals on X-ray diffuse scattering

Using the X-ray diffuse scattering technique, KCl crystals with various Ba impurity concentrations (0.0027–0.353 at. %) have been studied. Isointensity curves for all the crystals studied were constructed, which permitted discovering a strong concentration dependence of the diffuse scattering intensity. Starting with 0.0027 at. % Ba the Guinier-Preston zones appear in the {100} planes. At higher Ba concentrations their number (up to 7 planes in the zone) and sizes increase. The limiting Ba solubility in the KCl lattice is shown to be less than 0.0025 at. %. The diffuse spot elongation in the 〈130〉 directions at Ba concentration of 0.012 at. % results from diffraction effects of summation of spaces stress vectors acting in the 〈100〉 direction. The analysis of non-uniform Ba distribution in KCl gave the form and character of segregates which are described by a two-phase model. Shown is the effect of various impurity concentrations on the coherent coupling of the substance and matrix.     

Studies on large uniaxially grown benzophenone single crystals

〈110〉, 〈010〉 and 〈100〉 oriented uniaxial benzophenone crystals were grown by uniaxially solution‐crystallization method of Sankaranarayanan ‐ Ramasamy (SR). The experimental parameters involved in the present study were investigated in detail and a constant growth rate was achieved by compensating the loss of growth units in the solution. A transparent uniaxial benzophenone crystal having dimension of 500 mm length and 55 mm diameter was grown at room temperature for the first time in the literature. In contrast to the conventional solution growth method, the growth rate along each direction was measured at ease during the respective growth experiment by monitoring the elevation of the solid‐liquid interface and found to be 2, 4 and 6 mm/day along the 〈110〉, 〈010〉 and 〈100〉 directions respectively for a chosen supersaturation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies on twin boundaries in calcite crystals

Natural single crystals of calcite have been cleaved along (100) planes and cleavage faces have been etched in 2% and 3% citric acid solutions. Etching produces twin boundaries oriented in 〈010〉 directions. The etch pits on the two sides of the twin boundary are oppositely oriented. It has been conjectured that the rows of pits might have been formed due to etching of dislocations on twin boundaries. One to one correspondence of twin boundaries has been established on matched cleavage faces. This is further confirmed by studying the induced twin regions produced on a (100) cleavage plane by indenting that plane itself. The implications are discussed.     

Microstructures on {111} faces of stannic iodide single crystals

Single crystals of stannic iodide (SnI₄) havebeen grown using the controlled reaction between SnCl₂ and KI by diffusion process in silica gel medium. Orange to reddish octahedral stannic iodide crystals up to 3–4 mm in size have been grown at room temperature. Optical studies have been made on the various surface structures of {111} faces of the asgrown crystals. On octahedral faces of these crystals, triangular-shaped hillocks with growth layers in the 〈110〉 directions have been observed. Occasionally, growth spirals on octahedral faces have also been reported. Close loops of growth fronts have been investigated and have been interpreted. It has been suggested that two-diemensional nucleation, spreading and pilling up of triangular growth layers is mainly responsible for the growth and occasionally the growth is due to screw dislocations. The implications are discussed.     

Microplasticity of CsI crystals

The study of the mechanisms of plastic deformation of CsI crystals has found the participation of not only the main {110} 〈100〉 slip system but also of the secondary one {110} 〈110〉. Besides that, production and motion of point defects (or small prismatic loops) take place. The gliding on secondary slip system and the deformation accounted for by the generation and motion of point defects is facilitated at low temperatures and high deformation rates. The character of the motion and multiplication of dislocations in the main slip system is investigated. From the temperature and stress dependence of the mobility of isolated dislocations quantitative data on the thermally activated motion of edge dislocations on the main slip system have been obtained. It is shown that, as in the case of other alkali halides, the thermally activated motion of edge dislocations in CsI crystals on {110} 〈100〉 system is limited by their interaction with local obstacles.     

Growth and dissolution of BaFCl crystals

Single crystals of BaFCl have been growth by flux technique using BaF₂ and BaCl₂. Etching with formic acid revealed dislocation etch pits on (001) cleavage faces of the crystals, at room temperature. The influence of etching parameters such as undersaturation, temperature and concentration of poison in the etchant is studied. Decreasing the undersaturation of formic acid by reducing the percentage of water and increasing the temperature of the etchant were found not to have any effect on the morphology of etch pits. However, as the CdCl₂ poison concentration is gradually increased, the orientation of the pits change from 〈100〉 to 〈110〉 at high concentration.     

X-ray topographic investigation of growth defects in natural calcium fluoride crystals

Calcium fluoride crystals have been cleaved along {111} faces and the freshly cleaved faces have been chemically etched in 2.6 N nitric acid solution. The etched faces have been optically studied. One-to-one correspondence of dislocation etch pits have been established on the matched cleavage faces and on the opposite sides of thin flakes. The same crystal has been studied using X-ray topographic technique. By using 022 - and 02 2 reflections, stereopair projection topographs were studied and compared with the optical micrographs. The close resemblance between dislocation etch pits and dislocation out-crop images has been established. The orientation of the Burgers vectors of the dislocation lines has been identified using AgKα radiation with 111 -, 11 1- and 1 11 reflections. It has been confirmed that Burgers vectors of dislocation lines lie parallel to 〈110〉 directions. The implications are discussed.