Evaporation of doped NaCl crystals

In the present paper an investigation of the influence of impurity ions on the evaporation of NaCl crystals is reported. Monovalent impurities little influence the evaporation rate. The evaporating structures have changed only when there were extremal differences in the values of ionic radii. However, the bivalent impurities substantially influence the evaporation rate. This unfluence depends upon the fact whether the impurities are in non-associated or associated state with cation vacancies, respectively. This fact also affects the shape of evaporating structure.     

Structure sensitivity of relaxation phenomena in NaCl and KCl crystals doped with some divalent impurities (II) effect of plastic deformation

By studying: 1/the role of dislocations in the origin of the C-ITC-peak in undeformed crystals, 2/ the effect of plastic deformation upon the behaviour of this peak, and 3/ the recovery of the deformation-induced changes of the basic characteristics of this peak (H^C, T_M^C) it has been confirmed that dislocation lines surrounded by the Cottrell-like atmospheres can be considered as polarizable entities related with the high-temperature dielectrical response of as cleaved NaCl and KCl crystals doped with divalent impurities. The Maxwell/Wagner model of polarization effects in heterogeneous dielectrics satisfactory accounts for the majority of the experimental data. The quantitative analysis of the results obtained yields some additional informations concerning the interaction- and motion-parameters of the defects considered.     

Some features of plastic deformation of LiF and NaCl single crystals at high temperatures

The deformation of the (001) plane of LiF and NaCl by indentation and scratching at high temperatures was performed. The dislocation patterns arising from deformation were sharply different from those observed at room temperature. It was proposed the explanation of these results. The model of plastic flow in (001) indentation and scratching were considered. Anisotropy of hardness by the scratch method was revealed clearly at high temperatures. It was proposed the explanation of the anisotropy of hardness. The correlation was established between the dislocation structures observed near the indentations and scratches.     

Regularities of plastic deformation in indentation on the (111) plane of NaCl single crystals

Dislocation structures arising in indentation on the (111) face of NaCl single crystals are studied by etch-pit technique. The deformation temperature varied in the interval from 77 to 520 °K. The effect of radiation defects introduced by γ-irradiation on the shape of dislocation rosette was investigated. Three types of dislocation rosettes depending on the experimental conditions were observed. A possible explanation of this phenomenon is proposed. It is shown that the polarity of plastic deformation observed under indentation is an universal phenomenon which is revealed in the temperature range from 77 to 470 °K. The phenomenon of dislocation rosette inversion was first observed.     

Electron microscopic investigations of precipitates in doped NaCl crystals

Precipitation morphology of NaCl:CdCl₂ and NaCl:SrCl₂ crystals is investigated by high voltage transmission electron microscopy. The volume fraction of the precipitates and the content of CdCl₂ has been evaluated using the theory developed by Hillard. Selected area diffraction patterns of the precipitates and investigations of the misfit dislocations around the precipitates is presented.     

Correlation between the lattice parameters of crystals with perovskite structure

The correlation \((\bar a_2 + \bar a_3 ) = (\bar a_1 + \bar a_4 )\) has been established for the mean parameters of the reduced perovskite unit cells, \(\bar a_1 ,\bar a_2 ,\bar a_3 \) and \(\bar a_4 \) of four arbitrary compounds with the perovskite structure having the compositions (1) ABX₃, (2) A′BX₃, (3) AB′X₃, and (4) A′B′X₃, where A, A′ and B, B′ are the pairs of metal atoms with equal valences and X is an oxygen or halogen atom. The above correlation is consistent with the model of harmonic quasi-elastic atomic interactions.     

Localization of plastic deformation in Cu and Ni single crystals

The patterns of plastic flow in fcc Cu and Ni single crystals oriented in a way to provide easy slip are studied. The main space-time characteristics of deformation localization at the stages of easy slip and linear strengthening in these single crystals are established. The relation between the orientation of the sites of deformation localization and the crystallography of the slip systems in the samples is studied. The velocity of the motion of the deformation-localization sites during sample tension is determined.     

Serrated plastic deformation in LiF single crystals at high temperatures

The serrated plastic flow in LiF single crystals has been studied in the mode of active deformation at high temperatures (T = 573–1093 K). The parameters of the jumps in the deforming stresses (normalized amplitude and relaxation time of stress oscillations) were determined at the stage of strain softening under conditions of uniaxial compression and tension. It was shown that the jump parameters are essentially dependent on the type of the stressed state and the deformation temperature. The activation energy of serrated deformation in shear bands was established to be close to the migration energy for cation vacancies.     

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.     

Dielectric losses of alkaline earth doped KCl and NaCl crystals containing z centers

Results of measurements of the temperature dependence of dielektric losses (tan δ) in KCl:SrCl₂, KCl:CaCl₂ and NaCl:CaCl₂ samples after electrolytic coloration, after F → Z₁ conversion and Z₁ → Z₂ conversion are reported. In agreement with Rosenberger-Lüty model, Z₁ centers display dipolar character due to the presence of the ordinary Me²⁺-cation vacancy dipole with adjacent F center. The changes of tan δ after Z₁ → Z₂ conversion point to the release of a free cation vacancy from the former dipole.     

Mechanism of spatial ordering of dislocations during plastic deformation of crystals

Mechanisms of spatial ordering of dislocations during plastic deformation of crystals are considered. The system of evolution equations, which take into account the effects of elastic and correlated interactions of screw dislocations, is derived. The study is performed with due regard for the dynamics of spatial fluctuations of the dislocation density.     

Internal bias field in TGS crystals doped with different impurities

The influence of an internal bias field formed by impurity ions of heavy metals and alpha-alanine molecules on the dielectric nonlinearity and emission properties of ferroelectric triglycine sulfate crystals has been studied. It is shown that a role of defects increases near the phase transition, which manifests itself in a decrease in the maximum values of the effective permittivity and an increase in the emission current with increasing impurity concentration.     

Correlation between microhardness and dislocation mobility in crystals with a different type of bond

The complex investigations of microhardness and dislocation mobility in temperature interval 77–873 K have been performed on ionic crystals, semimetals and covalent crystals. It is shown that the correlation between the microhardness and dislocation mobility exists as a whole only. The temperature change of microhardness is not often connected with the change of dislocation mobility. An “anomalous” behaviour of semimetals has been established – they have a small microhardness and a low dislocation mobility at a time.     

Comparison of lead solubility in NaCl crystals from data obtained by different methods

The solvus of the NaCl: Pb²⁺ system was found in the concentration range from 1.5 × 10⁻³ to 1.9 × 10⁻² mol% at temperatures ranging from 375 to 430 °C from the data of flotation measurements of the crystal density. The heat of impurity dissolution equal to 2.0 ± ± 0.6 eV and the change in the vibrational entropy in the formation of the solid solution S_v/K= 20 ± 10 were determined. Reasons for a difference in the estimates of lead solubility in NaCl, obtained from temperature dependences of light scattering and by other methods: measurement of the density, electric conductivity, and the electron-microscopic decoration of the same crystals are discussed.     

Connection between electrical and deformation characteristics of PbS crystals

The influence of plastic deformation on temperature dependence of carrier concentration n and mobility μ in PbS crystals has been studied. Comparison of the results obtained with selective etching patterns from original and deformed crystals makes it possible to conclude that during the plastic deformation there takes place a dissolution of precipitates by passing of dislocations through them. As a results, rows of point defects appear along the path of dislocation movement which may be the cause of a change in n and μ due to deformation. A change in the electron scattering mechanism below 110 K has been discovered.     

Basal twinning as a room temperature plastic deformation mode of chromium- and titanium-doped sapphire crystals

The degree of basal twinning caused by indentation was determined quantitatively on a series of chromium and titanium doped sapphire crystals with variours dopant contents. It depends on the dopant content significantly. The effect of titanium ions in reducing the degree of twinning is more pronounced than that of chromium dopants. This “size effect” of the dopant ions is consistent with the mechanism of basal twinning as reported by KRONBERG .     

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.     

Effect of plastic deformation of the thermoluminescence of γ-irradiated NaCl and KCl Crystals

The overall thermoluminescence (TL) intensity of γ-irradiated NaCl crystals initially increases and then decreases with the number of newly-created dislocations. However, the overall TL intensity of γ-irradiated KCl crystals increases with the increasing number of newly created dislocations. The TL spectra are recorded for different plastic deformations at different temperatures. It is found that the plastic deformation has no considerable effect on the TL spectra of γ-irradiated NaCl and KCl crystals. Trap destruction model and trap competition model are discussed for the decrease in the TL intensity with deformation of the crystals. The physical ideas behind the increases in the relative intensity of glow peaks and the appearance of new glow peaks are explored.