Amplitude dependence of the internal friction of alkali-halide crystals in an electric field

The influence of an electrical field on the internal friction of an alkali-halide crystal (AHC) was investigated for relative deformation amplitudes corresponding to separation of dislocations from fastening centers, and for higher amplitudes when plastic deformation of the specimen occurs in an ultrasonic wave field. The influence of the electrical field in the deformation domain under consideration reduces to direct action on charged dislocations, re-orientation of dipole fastening centers, and activation of sources in block boundaries.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 5–11, August, 1989.The author is grateful to Dr. N. A. Tyapunina for valuable comments, remarks, and unchanging interest in the research.     

Internal friction of deformed zinc single crystals

Zinc single crystals with the side in a (0001) basal plane were elongated and the internal friction measurements were carried out as a function of temperature in the mode of a flexural vibration. Two relaxation peaks were observed to appear: one at around 500°K and the other at about 570°K. Each activation energy was obtained 0.70±0.08eV and 1.01±0.06eV, respectively, by the peak shift method. The experimental results were discussed in terms of dislocations in pyramidal slip system {$\text{11}$22} 〈11$\text{2}$3〉 and twinning dislocations in the planes {$\text{1}$012} 〈10$\text{1}$1〉, respectively.     

Dislocation interaction with radiation defects in alkali-halide crystals

A mechanism of room-temperature irradiation-induced strengthening of alkali-halide crystals (AHCs) is suggested. It is shown that the deformation-stimulated luminescence is a result of the destruction of hole color centers, which strengthen AHCs, by dislocations.     

Bulk modulus of alkali-halide mixed crystals

By using the bulk moduli of the pure and components we calculate, for various compositions, the isothermal bulk modulus of the following mixed crystals: NaCl-NaBr, KCl-KBr and KBr-Kl. The calculated values are in good agreement with the most recent experimental data.     

Optical characteristics of alkali-halide crystals doped with nickel ions

Scientific-Research Institute of Mechanics and Physics at the Saratov State University, 112-A, Bolshaya Kozach'ya Str., Saratov, 410071, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 3, pp. 235–238, May–June, 1995.     

Positron states in alkali-halide single crystals

Detailed consideration is given to the annihilatory decay of positron states in real alkali-halide single crystals of defective structure. Representations of the exciton-positron states in the matrix of the crystal and close to a lattice defect are analyzed. On the basis of these representations, expressions are derived for the yield of the three-quantum decay process and the intensities of the components contributing to two-quantum annihilation; the expressions agree with existing experimental data. It is shown that the greatest contribution to the three-quantum decay arises from an exciton-orthopositronium state located in the vicinity of the defect.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 76–79, October, 1974.     

Off-center substitutional ions in alkali-halide crystals

The potential wells of alkali and halogen ions as impurities in alkali halides are investigated by means of a deformation-dipole model with single-ion parameters. The calculations indicate that Li⁺ is off center in seven and F^? in six of the sixteen rocksalt-type crystals considered. In about half of the off-center systems the configuration has D_4h symmetry if the impurity is kept at its lattice position. The minimum-energy configuration of the off-center system KCl:Li⁺ is calculated in detail, and the influence of hydrostatic pressure is investigated. Our results are in qualitative agreement with experiment.     

Metallization of alkali-halide crystals under superhigh pressures

An estimation, based on thermodynamical considerations, of the pressure under which the NaCl crystal transforms into the metallic state, was carried out. Using the method of composite atomic orbitals, the thermodynamic potentials of dielectric and metallic phases of the NaCl crystal were calculated. The equations of state were obtained for both phases in a wide range of pressures, from 0 to 2000 kbar. From the point of intersection of the curves of thermodynamic potentials of two phases, the determination was made of the pressure of metallization equal to 1350 kbar. The temperature effects were not taken into account.Translated from Izvestiya VUZ, Fizika, No. 3, pp. 57–62, March, 1973.     

Formation of near-defect excitons in alkali-halide crystals

Pulsed-spectrometric research shows that the presence of defects, including those that are electrically neutral with respect to the crystal lattice, has a significant influence on the distribution of the radiation-induced electron excitations. This is evident in the electron-excitation sink in the vicinity of defects and the formation of localized excitons around impurities in ionic crystals. This influence of defects on the electron-excitation distribution is probably due to deformation of the lattice in the region of the defect. It is shown that, in the region of the defect, there is oscillating potential relief, the presence of which leads to the capture of charge carriers and their localization in this region. Lattice distortion because of deformation in the region of the defect changes the mutual distribution of the ion pairs. This creates conditions for the effective conversion of electronic excitations to localized near-defect dihalide excitons, which are different from those created in an ideal lattice. Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 94–108, November, 1996.     

Internal friction in cd+zn alloy single crystals

Internal friction measurements were used for the examination of Cd + Zn alloy single crystals. It was established that the interaction energy between solute Zn atoms and dislocations in basal planes is 0·12 eV.The authors thank Dr. P.Luká, CSc., for valuable discussions.     

Influence of an electric field on the amplitude dependence of internal friction of alkali-halide crystals at low amplitudes

Application of an electric field of intensity 10⁵–10⁶V·m^–1 to alkali-halide crystal specimens results in the appearance of an amplitude dependence of the internal friction (IF) in the low amplitude domain of the relative deformation 10^–7–10^–6, where the amplitude dependence of the IF has a peak. A physical model is proposed that is based on the assumption of shifting of the dislocation under the action of the electric field into a new less secure equilibrium position. The growing and decreasing branches of the IF peak are described within the framework of this model. The question of the amplitude dependence of dynamic IF losses is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 47–50, December, 1989.In conclusion, the authors are grateful to Doctor of Physicomathematical Sciences N. A. Tyapunin for discussing the research, useful remarks, and comments.     

Temperature dependence of young's modulus for alkali-halide crystals

This apparatus gives readings for Young's modulus E and for the velocity of sound c as functions of temperature t. It is found that — dE/dt for the halides of Na and K increases with the lattice energy in a regular fashion.I am indebted to Professor A. A. Vorob'ev for direction and assistance in this work.     

Evidence for a positron-exciton insulator in alkali-halide crystals

The angular correlation of annihilation photons for single crystals of 60% KCl-40% KBr solid solutions and X-irradiated NaBr crystals were measured. For 60% KCl-40% KBr samples the measurements of the angular correlation curves were carried out under an external magnetic field of 13.0 kG. The experimental data and theoretical estimations show that thermalized positrons, captured by free cation vacancies, form the positron centre of F₄-type; if the positrons are localized near the complex defects, containing the cation vacancies, the formation of peculiar “positron-exciton complex” of the positronium-like type is realized.