TEM and X-ray investigations of defect structure of PbSnTe crystal

The Pb_0.8Sn_0.2Te single crystal grown by the Bridgman technique was examined by X-ray and TEM methods. The X-ray reflection topography revealed that the PbSnTe crystal consisted of monocrystallinic blocks with linear dimensions of 1–5 mm separated by low angle boundaries of tilt-twist character. “As grown” defects observed by TEM method have been identified as single perfect dislocations and dislocation pairs. A mean density of dislocations inside the crystal blocks was no more than 10³ cm⁻². Except “as grown” defects rows of mobile dislocations were observed. All of dislocations lines were characterized by the same type of Burgers vector, i.e. b = 1/2a〈110〉.     

X-ray investigations on the defect structure of KCl with Cd++ impurities

A systematic defect characterization by X-ray diffraction was carried out on crystalline KCl system with Cd⁺⁺ impurities at various levels, viz. 2, 4, 6, 8, and 10 mole%. Quantitative estimation of the amount and nature of defects was done from the integrated X-ray intensity measurements of the samples. Further analyses of the experimental data indicate enhancement of the Debye-Waller factor with concentration of Cd⁺⁺ impurities. The measured density and the cell constant values at room temperature yield vacancy estimations for the system. The observed change of Bravais lattice of the system for Cd⁺⁺ concentrations from 4 mole% with appreciable enhancement of intensity of Bragg reflections of mixed indices are reported and discussed.     

Screw dislocation core structure and plastic deformation of BCC Metals

The core structure and an energy distribution around a screw dislocation core in model bcc lattice have been investigated in both unstressed and stressed states to clarify the controlling factors which determines the core type and the shape of PEIERLS potential. In the case of iron total four types of core structure were obtained, namely, unpolarized, polarized, split and high energy position and the shape of PEIERLS potential was so-called camel hump type which gives a steadfast explanation for the presence of a hump on the yield stress — temperature curve of iron single crystal. The calculated results for the spatial distribution of the PEIERLS potential around a core show that the range of distribution is relatively small in the low PEIERLS stress case (iron), but is large in high PEIERLS stress case (vanadium).     

Defect recovery after 77 K plastic deformation in bismuth

Dopplerbroadening measurements were performed in 77 K deformed bismuth in the temperature range between 80 K and 410 K. An important trapping effect was observed. Two recovery stages were found, one at 230 K and the other at 380 K. The measurements were compared with the results obtained from positron annihilation lineshape measurements in as-received polycrystalline bismuth samples of different purities, and in room temperature deformed bismuth samples. In all samples a recovery stage at 380 K was found, which is ascribed to the annealing of dislocations. Lifetime measurements were performed in the as-received bismuth samples. For dislocations a lifetime of 289 ps was found.     

Effect of the defect structure character in calcite single crystals on X-ray diffraction

The paper presents experimental results for the dependence of the integral intensity of anomalous transmission T_i and Laue reflection R_i of X-rays on the structural quality of calcite single crystals as obtained by a two-crystal spectrometer. The relation between X-ray dynamic and kinetic scattering as a function of the sample thickness, densities of perfect dislocations in perfect CaCO₃ crystals and of atom-vacancy complexes in calcite crystals with „background”︁ has been found. Distortions due to perfect grown-in dislocations in calcite are shown to exceed those produced in crystals with „background”︁. The latter appear to be more X-ray transparent. A comparison with results of twin layer thickening experiments on CaCO₃ crystals of different qualities again points to the different nature of these distortions. In CaCO₃ crystals with the dislocation density of up to 2 × × 10³ cm⁻², the X-ray scattering, in our experiments, was consistent with the dynamic diffraction theory, while at higher dislocation densities, the X-ray scattering markedly differs from it.     

X-ray investigations of surface roughnesses

The unique potentialities and prospects for practical use of the X-ray scattering method as applied to the study and testing of surface roughnesses are considered. The high sensitivity, informative capability, and reliability of this method are demonstrated by using numerous examples. The results obtained by the X-ray scattering method at different wavelengths are compared with the available data of atomic-force microscopy.     

X-ray absorption near edge structure spectroscopy (XANES) investigations of amorphous alloys

The paper outlines recent successes in deriving particular structural information about amorphous alloys from X-ray absorption near edge structure (XANES) spectra. Examples of such information are (1) an estimation of the validity of structural models, (2) evidence for three-body-correlations and (3) the detection of preferred chemical bonding and a resulting microphase segregation in multicomponent amorphous alloys. The examples presented help to assess the potential of the relatively new method of XANES calculations and will stimulate further studies of non-crystalline materials.     

Role of twinning in plastic deformation

A new concept of the structure of yttrium-aluminum garnet (Y₃Al₅O₁₂) has demonstrated the possibility of forming inversion twins in the (111) plane. The twinning processes are shown to be responsible for stress relaxation during the growth and plastic deformation of Y₃Al₅O₁₂ single crystals. This way of stress relaxation can be used to describe the plastic deformation of other crystals, at least cubic ones.     

Study of the defect structure of paratellurite crystal using multiwave diffraction and normal X-ray diffractometry methods

Multiwave X-ray diffraction has been used to study the structure of crystalline samples. A cycle of local measurements of rocking curves (RCs) of the (220) and (371) reflections under conditions of multiwave diffraction (MD) has been carried out in a paratellurite crystal. The data obtained are used to compare the sensitivity to structure defects of two-beam diffraction with that of MD, which makes it possible to study the X-ray wave phase. The comparison has revealed a higher ability of the phase-sensitive method to detect defects.     

Influence of plastic deformation on the photoconductivity of CdTe

Investigation of photoconductivity have been performed on p-type phosphorus doped CdTe (5 × 10¹⁵ cm⁻³) deformed by compression at room temperature. Using a technique of axial illumination, the contribution of the surface to the photoconductivity is suppressed. In the investigated energy range (0.08–1.54 eV), and at room temperature, a maximum of the signal of the non-deformed material is of found at 1.312 ± 0.009 eV, with a half width of 0.100 eV, whereas the 0.3% deformed material presents a maximum at 1.348 ± 0.009 eV with the same half width. At 223 K these peaks are shifted to higher energies, the half width remaining unchanged, and the amplitudes being ∼ 30 times higher.     

Growth,X-ray structure and optical investigations of epitaxial films of solid solutions of lithium niobate-tantalate

Processes of the liquid phase epitaxy of films of solid solution of lithium niobate-tantalate grown from the limited plane-parallel volume of the liquid phase is considered in the paper. Morphological and structure characterstics of films are investigated. The possibility of the effective use of the obtained structures as active elements of the integrated optics is shown.     

Inhomogeneities of the plastic deformation of MgZn2 single crystals

Single crystals of the Laves phase MgZn₂ of different chemical composition within the range of homogeneity were deformed by dynamic compression at temperatures from 300 to 500°C. The surfaces of the specimens were observed by light microscopy. Special types of inhomogeneities of deformation (Lüders bands, macro-slip steps) are described and first conclusions are drawn concerning the behaviour of dislocations in this substance.     

Study of characteristics of plastic deformation in amorphous Fe-Cr-Mo-V-B-Si alloy by the method of local deformation

Characteristics of plastic deformation in the amorphous Fe-Cr-Mo-V-B-Si alloy have been studied by the method of local deformation. It is established that plastic deformation in the rapidly quenched iron-based alloy proceeds by two channels. The model for interpreting the energy aspects of plastic deformation in amorphous materials is suggested.     

On the initial stage of plastic deformation of sulphur-doped gallium phosphide

The overall deformation behaviour between room temperature and 1000 K has been investigated by bending and uniaxial compression at small strains ≦ 0.1%. Ductile-to-brittle transition temperature was found at 44% of the melting point. Dislocations are generated mainly at surface irregularities. Whereas screw dislocations predominate at the beginning 30° and 60° segments become more important after cross slip and interaction of different slip systems.     

X-ray diffraction topography and diffuse scattering techniques applied to study the defect structure of plastically deformed al single crystals

X-ray diffraction topography and diffuse scattering techniques were used to study the defect structure formation of plastically deformed Al single crystals. The investigated X-ray scattering has been found out materially to depend upon the character of the dislocation structure (upon the geometry of the dislocation distribution). This dependence is manifested in different distribution of the intensity and in the changed form of the isointensity curves of diffuse and regular (Laue) reflections. In spite of the fact that the distribution of the internal stresses acting in different glide systems under conditions of uniaxial stretching is of complicated character, it is possible to trace the development of the glide process in the body of a sample and to obtain satisfactory interference patterns both of regular reflexions (on topograms) and of diffuse ones (on Laue photographs) up to severe deformations of a crystal at 300, 4.2, and 1.6 K. The following diffuse effects connected with structural changes in deformed crystals have been ascertained on the X-ray photographs:

• —diffuse regions are elongated in the reciprocal lattice space along the glide directions or other crystallographic directions;
• —these diffuse regions are split into separate areas along the directions of the said elongations;
• —the diffuse regions are changed in length: the diffuse reflexes are diffused or condensed;
• —the diffuse scattering isointensity curves are “zigzag”-shaped.

     

X-ray and neutron diffraction study of the defect crystal structure of the as-grown nonstoichiometric phase Y0.715Ca0.285F2.715

This work begins a series of papers aimed at studying the defect structure of nonstoichiometric phases R _{1 ? y} Ca _y F_{3 ? y} with a tysonite-type (LaF₃) structure. In the single-crystal structure of Y_0.715Ca_0.285F_2.715 with a tysonite-type small unit cell (sp. gr. P6₃/mmc, a = 3.9095(2) Å, c = 6.9829(2) Å; Z = 2; R _w = 2.16%), the displacements of Y³⁺ cations and F^2? anions from 6₃ symmetry axes were observed for the first time. The X-ray diffraction pattern shows weak satellites insufficient for structural calculations. The LaF₃ structure type is stabilized up and down on the temperature scale due to anion vacancies and the symmetrizing effect of Ca²⁺ cations lying on 6₃ symmetry axes. At 120°C the fluoride-ion conductivity in the nonstoichiometric phase Y_0.715Ca_0.285F_2.715 is five orders of magnitude higher than that in the stoichiometric phase β-YF₃. The transition to a superionic state is caused by a deviation from stoichiometry and is not associated with reconstructive phase transformation.     

X-ray investigations of BaLaGa3O7 single crystals

X-ray investigations have been carried out on single crystals of BaLaGa₃O₇. Debye temperature as well as thermal expansion coefficients were determined, and values of which are respectively