Dislocation internal friction and temperature dependence of yield stress in high-purity molybdenum single crystals

High purity molybdenum single crystals (residual resistivity ratio ≈ 6 · 10⁴) were studied by means of computer-controlled internal friction technique at frequencies of about 100 kHz in the temperature range 6 to 300 K. The amplitude dependences of decrement were measured within the vibrational strain amplitude 10⁻⁷ to 10⁻⁴. It was established that the temperature dependence of ultrasonic amplitude providing a constant level of reversible dislocation deformation coincides well in relative units with the temperature dependence of the critical resolved shear stress at 20 to 180 K.     

Variation of low temperature internal friction at microplastic deformation of high purity molybdenum single crystals

Amplitude and temperature spectra of ultrasound absorption in weakly deformed high purity molybdenum single crystals of different orientations were measured. The results were discussed in terms of parameter changes related to quasiparticle- or dislocation oscillations, respectively, dislocation-point defect interactions as well as defect generation at microplastic deformation.     

Dielectric,piezoelectric, elastic properties and internal friction of TGSe crystals with large unipolarity

In this work we have studied influence of temperature and external electric field on dielectric, elastic, piezoelectric properties and internal friction of D, L-α-alanine doped triglycine selenate crystals. Experimental result analysis allows to conclude that ferroelectric materials with stable physical properties may be created on doping crystals foundation.     

X-ray investigations of friction stressed α-Fe single crystals

A translation of a α-Fe single crystal on a glass plate causes elastic and plastic deformations in regions near the surface. The dislocation density caused by the deformations and its dependence on the friction way were determined from Rocking curves. After having reached a certain friction way the monocrystalline surface layer changes into a polycrystalline layer. At the same time a friction texture develops within the polycrystalline layer.     

Modulus and internal friction in phosphate-silicate bioactive glass

The real and imaginary parts of the dynamic shear modulus, G′ and G″, respectively, of a “bioactive glass” Na₂O, CaO, SiO₂, P₂O₅ have been measured from 10^?4 Hz to 1 Hz at temperatures from 160 K to 610 K. The mechanical loss tangent of the glass (T_g = 816 K) at 1 Hz shows two relaxation regions: one centred at 312 K and the second at 585 K. The low-temperature peak appears in the same region as the peak attributed to Na ion motion in silicate glasses. The modulus of the glass is 32 GPa at 295 K. The spectrum of the high temperature peak has a broad distribution of relaxation times with a half width of five decades of frequency, and Arrhenius “activation energy” of 164 kJ mol.^?1, and the amplitude of this relaxation decreases on cooling. The similarity of these features with those observed in rigid molecular and other types of glasses suggests that the relaxations observed in the bioglass may be more appropriately considered as an intrinsic property of the non-periodic arrangement of atoms or ions in a solid than as being due to the diffusion of specific types of ions in it. It is pointed out that isothermal and isochronal measurements of internal friction in glasses do not give the same relaxation rate at the same temperature, due mainly to a rapid decrease in the amplitude of relaxation with temperature. The shear, Young's and bulk moduli of the glass are, 31.9, 76.6 and 43.0 GPa, respectively, and the Poisson's ratio is 0.20.A sample of the same bioglass containing 0.05% more water showed a shoulder in its tan φ at ～ 400 K and a peak at ～ 560 K, with little change in its modulus or T_g. Thus the presence of water above a certain amount had less significant effect on the internal friction of the bioactive glass.     

Ain single crystals

Single crystals of aluminum nitride up to 1 cm long and 0.3 in diameter have been grown by a sublimation-recondensation technique at about 2250°C. The starting material is prepared by the direct reaction of aluminum and nitrogen at 1850°C. The crystals are grown at a rate of 0.03 cm/hr. in sealed tungsten crucibes in an rf heated tungsten furnace. They are amber in color and have the wurtzite structure.     

Specific Features of the Formation of Gallium,Indium, Bismuth,and Antimony Nanoparticles

Crystallography Reports - Gallium, indium, bismuth, and antimony nanoparticles were obtained by vacuum evaporation technique onto glass carbon substrates at an argon gas pressure of 6 × 103 Pa...     

Total internal reflection in anisotropic crystals

Examples of total internal reflection manifestation have been considered on the basis of a solution to boundary problems of crystal optics using the Berreman matrix method and applying the Mathematica-5 system. It is shown how optical activity manifests itself in the total internal reflection and how this effect can be used to monitor the quality and homogeneity of film coatings.     

Evolution of twin-boundary geometry in Bismuth crystals with an increase of load

The effect of an increase in an external static load on the shape of wedgelike twins formed in the vicinity of stress concentrators in Bi crystals has been studied. A new method for investigating the intermediate stages of mechanical twinning in metals is suggested. It is shown that the applied load is not the determining factor in the development of plastic deformation via twinning in metal crystals.     

Impact damage in MgO single crystals

Optical absorption has been used to study the impact damage in MgO and MgO:Li single crystals. The results are similar to that obtained in compressed crystals, except in MgO:Li with stable Li° defects, in which the impacts do not produce an increase of the 5.7 eV absorption band.     

Included and occluded grains in iron single crystals

The paper presents some experimental results concerning the occurrence of stray grains in high-purity iron single crystals grown by the strain-anneal method. The experimental results indicate that the stray grains are either the unabsorbed grains from the polycrystalline matrix with twin orientation or true annealing twins. The iron crystals with a small number of stray grains can be prepared when a steep temperature gradient is used during growth.     

Dislocation formation and motion in germanium single crystals

The dislocation structure of germanium single crystals used in IR optics is investigated. The effect of high-temperature annealing on the dislocation distribution in Ge single crystals is shown.     

Ordering and magnetostriction in Fe alloy single crystals

Short-range and long-range ordering in α-Fe terminal solid solution phase (A2 phase with bcc structure) influences its physical, mechanical, magnetic and magnetostrictive behavior. Single crystal sample forms are ideal for examining order in these alloys using X-ray and neutron scattering techniques. Limited structural information available suggests that the lattice of A2 phase at room temperature contains a mixture of regions with local atomic environments similar to those expected in the long-range ordered structures in stable/metastable equilibrium with the A2 phase. The nature and extent of these regions are sensitive to alloy composition and the thermal history. The lattice strain modulations result from the nature of solute atom distribution (short-range ordering) in each region and impact the physical, mechanical, corrosion and magnetic behaviors. A need for a fundamental understanding of ordering in Fe and other alloys through structural evaluations of local atomic environments in alloy single crystals is suggested in this review.     

Low-angle boundary investigation in silicon single crystals

Low-angle boundaries in Si single crystals grown from the melt in [111], [100], [112], [110], [118] and [115] directions were investigated by chemical etching, copper decoration technique and X-ray topography. — LAB of four types were found in planes parallel to the crystal growth axes. Rearrangement of dislocations from slip bands into LAB was observed in heavily-doped Si crystals. The origin of LAB in melt grown Si crystals is discussed. It is shown that these boundaries are well interpreted in terms of dislocation alignment formation in the thermal stress field of the growing crystal.     

Growth and morphology of p-terphenyl single crystals

The results of a preliminary investigation of the growth and morphology of p-terphenyl crystals grown by sublimation and by solvent evaporation methods are reported. It was observed that lozenge–shaped (001) crystal plates are obtained from xylene and benzene solution while dendritic crystals by sublimation. Crystallographic orientation of the plates and microscopic observations of as-grown crystal surfaces are also described.