On hardening of crystals by immobilization of dislocations due to mobile impurities

A theory describing the effect that impurities have on the regularities of the plastic deformation of crystals in terms of dynamic strain aging is developed. This theory is a combination of two models, one of which describes the immobilization kinetics of individual dislocations due to the entrainment of impurities, while the second considers the collective dynamics of the dislocation ensemble. The unified model proposed here makes it possible to calculate the concentration and temperature dependences of the contribution that impurity atoms make to the flow stress. This theory explains the anomalous temperature dependence of the yield stress, which is experimentally observed in a number of materials.     

Impurity effects on low-angle boundary formation in silicon single crystals

The combined effects of crystal growth conditions and impurity (Sb, P, B, Ga) concentration on low-angle boundary (LAB) formation in silicon single crystals growing by Czochralski technique was investigated. The dependence of LAB formation frequency and LAB parameters on crystal growth conditions and impurity content was found. Impurity effects on LAB formation become apparent at concentrations of about 10¹⁸ cm⁻³. – All impurity investigated decreases the probability of LAB formation, the acceptor impurity influence is stronger. At B concentration exceeding 2 · 10¹⁹ cm⁻³ LAB formation does not occur. – Results are interpreted in terms of scheme of LAB formation in thermal stress field of growing crystal. To explain observed impurity effects assumptions about dislocation drag and about raising of critical stresses for dislocation generation with doping are made.     

Refractometry of TGS crystals doped with L-threonine impurity under uniaxial pressure

The temperature and spectral dependences of the refractive indices of triglycine sulphate (TGS) crystals doped with L-threonine impurity have been investigated. It is established that the introduction of an impurity weakens the temperature dependence of refractive indices. The electronic polarizability, refractions, and parameters of UV oscillators of mechanically deformed impurity crystals are calculated. The temperature coefficients of the phase transition shift are determined.     

Modeling the distribution of Ga and Sb impurities in Ge‒Si single crystals grown by double feeding of the melt: Growth conditions for homogeneous single crystals

Mathematical modeling of the distribution of Ga and Sb impurities in homogeneous (with respect to the content of the main components) single crystals of Ge–Si alloys, grown by double feeding of the melt, has been performed in the Pfann approximation. It is shown that the axial gradient of impurity concentration in Ge–Si crystals can be controlled in wide limits by changing the ratio of crystallization rate and the rates of feeding of the melt by silicon and germanium rods. The conditions for growing alloy single crystals, homogeneous both with respect to the content of the main components and to the impurity concentration distribution, have been determined.     

Hardening of crystals caused by the dynamic aging of dislocations

A model relating the pronounced effect of mobile impurities on the processes of plastic deformation in crystals to the dynamic aging of dislocations is proposed. The model is based on the concept of internal stresses depending individually on the age of dislocations due to the difference in the impurity environment. The concentration dependence of the impurity contribution to the hardening of materials is calculated. The theory is illustrated by the experimental data for a GeSi solid solution.     

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.     

Growth conditions and electric properties of KDP crystals. I. Conductivity measurements

Conductivity of potassium dihydrophosphate (KDP) crystals grown from solutions with different pH has been studied with due regard for the sectorial structure and the impurity composition of the crystals grown. The dependence of the conductivity parameters on these two factors is established. The data obtained lead to a conclusion on the formation of the real structure important for various electro-optical applications of KDP crystals and provide the optimization of growth conditions.     

Magnetoplastic effects in crystals in the context of spin-dependent chemical kinetics

Possible mechanisms of a number of magnetoplastic effects in magnetically disordered crystals are analyzed in the context of the chemical kinetics of reactions occurring in a system of structural defects upon plastic deformation. Particular attention is given to spin-dependent reactions between real-structure elements containing paramagnetic centers (dislocation cores, impurity centers, electronic excitations, and so on). It is shown that reactions of several types may occur between these elements, and, in some cases, the relative deformation rate can be related to the rate constants of intracrystalline spin-dependent reactions.     

The influence of magnetic effects on the mechanical properties and real structure of nonmagnetic crystals

This review for the first time systematizes the results of our investigations into the influence of magnetic effects on the mechanical properties and the real structure of nonmagnetic crystals. It is found that the preliminary magnetic treatment of alkali halide crystals leads to a decrease in their solubility and a change in the microhardness and yield stress. The magnetic field strongly affects the macroplasticity of LiF, NaCl, and PbS crystals under deformation in a magnetic field. This is accompanied by a change in the shape of stress-strain curves, a shortening of deformation stages, a change in the hardening coefficients, and a decrease in the yield stress. It is revealed that the magnetic effects exhibit threshold behavior. The yield stress is measured as a function of the magnetic induction and the strain rate. It is established that the magnetic and electric fields have a joint effect on the kinetics of plastic deformation. A kinematic model of the macroscopic magnetoplastic effect is proposed.     

In-situ Observations on Dynamic Processes Associated with Stacking Faults and Deformation Twins in Silicon Crystals

Stacking faults and thin deformation twins are observed to develop during the in-situ deformation of silicon crystals at elevated temperatures in a HVEM. Both the nucleation and the motion of partial dislocations take place under the applied stress in the regions of the stress concentration. Twinning dislocations moving on twin boundaries are extremely flexible. The spontaneous nucleation of loops of twinning dislocation on twin boundaries is observed rather frequently. No pole mechanism is observed to be operating. Stacking faults and deformation twins interact with glide dislocations moving along the intersecting planes by various ways.     

Zur plastischen Verformung von Antimoneinkristallen im Druckversuch bei Raumtemperatur

The plastic deformation of antimony single crystals dynamically tested in compression at room temperature has been investigated. As macroscopic deformation mechanisms twinning, dislocation slip, and kinking have been observed. The critical resolved shear stress for basal slip and twinning was measured and the orientation dependence of the deformation mode was explained. It is shown that basal slip dominates compared to rhombohedral slip.     

Thermal conductivity of FeS2 pyrite crystals in the temperature range 50–300 K

The thermal conductivity of two single-crystal samples of pyrite FeS₂ are investigated by the method of stationary longitudinal heat flux in the temperature range 50–300 K. The low electrical conductivity of the crystals with a small impurity content causes an identical value of experimental lattice thermal conductivity. The temperature dependence of the phonon mean free path is established.     

Growth of semiconductor silicon crystals

This paper focuses on the recent developments in Czochralski (CZ) crystal growth of silicon for large-scale integrated circuits (LSIs) and multi-crystalline silicon growth using a directional solidification method for solar cells. Growth of silicon crystals by the CZ method currently allows the growth of high-quality crystals that satisfy the device requirements of LSIs or power devices for electric cars. This paper covers how to obtain high-quality crystals with low impurity content and few point defects. It also covers the directional solidification method, which yields crystals with medium conversion efficiency for photovoltaic applications. We discuss the defects and impurities that degrade the efficiency and the steps to overcome these problems.     

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.     

The Effect of Intermolecular Interaction of an Impurity with its Environment on the Spectral Properties of Molecular Crystals

The energy spectrum and the spectrum of light absorption by impurity crystal are studied taking into account a nondiagonal perturbation caused by an impurity molecule. The effect of the intermolecular guest-host interaction on the conditions of existence of in-band resonance states is analysed and the frequency dependence of the half-width and the intensity of the resonance impurity absorption peak is obtained. The band absorption spectrum is calculated in the nearest-neighbour-approximation for one-dimensional and three-dimensional impurity crystals.     

Dynamics of twin layer widening in In-Pb crystals

The authors studied mobility of boundaries of plane-parallel twin layers in In-0.2 wt.% Pb and In-2 wt.% Pb crystals in the temperature range 290–373 K when stresses are applied τ/G = (1.35 – 7) × 10⁻⁶ (G is the shear modulus). They found that lead concentration increase as well as dislocation structure deterioration result in lower boundary velocity for a constant stress. In In-2 wt.% Pb crystals, the boundary velocity is well describable as V_n = V₀(τ) × × exp [ − ΔH (τ)/kT] where V₀(τ) = Ae^ατ/G (A = 10⁻³ cm/s, α = 1.1 × 10⁶) τ ΔH(τ) is the activation energy depending on the stress, ranging under these circumstances from 0.33 to 0.43 eV. At present it is difficult to interpret the results at hand. The analysis allows only to assume that the change in the boundary movement activation energy for impure crystals as against that for pure ones can be associated with the impurity effect on the structure of the intermediate zone between the twin and the matrix. The dependence of the pre-exponential factor on the stress is probably due to the effect of the internal long-range stress field on sources of twinning dislocations. Comparison with data for calcite and pure indium shows that twin boundary mobility parameters and their dependence on the stress are governed by the crystal type and defect structure.     

Dynamics of twin layer broadening in indium

The mobility of plane-parallel twin layer boundaries in indium crystals has been studied in the 235–390 K temperature range under stresses, τ, of (0.25–20) g/mm² (static load) and (35–335) g/mm² (crest values under impact load). For τ/G = (0.2–0.6) × 10⁻⁵ (G is the shear modulus), the process of twin layer broadening has been shown to be thermally activated; the process parameters and their stress dependence have been found. – Possible mechanisms of twin layer broadening have been analysed, and it has been concluded that a pole mechanism is inadequate to treat the results obtained. The twin broadening is considered to be due to nucleation and motion of twinning dislocations along boundaries in each subsequent twinning plane; it has been shown that the thermal activation parameters measured while broadening a twin layer, can be inconsistent with the elementary acts of broadening process (nucleation or motion of twinning dislocations). A deep gap between data on stress dependence of the activation energy of twin layer broadening for indium and calcite crystals and the Sumino theory is explained by the determining influence of the real imperfect structure of specimens on the process studied.     

Internal stress in doped NH<Subscript>4</Subscript>Cl:Mn<Superscript>2+</Superscript> crystals

The relationship of the effect of impurity on crystal growth and morphology, along with the internal stress and anomalous birefringence arising upon impurity trapping by a growing crystal, is considered. The NH₄Cl-MnCl₂-H₂O-CONH₃ model system and the heterostructural NH₄Cl:Mn²⁺ crystals formed in it are experimentally studied. It is found that up to 6.63 wt % Mn²⁺ impurity is effectively captured by growing NH₄Cl crystals at an impurity trapping coefficient only slightly below unity. The effect of Mn impurity stabilizes the full-face growth of NH₄Cl crystals with a rhombododecahedral habit in aqueous solutions and a cubic habit in water-formamide solutions. The trapping of manganese impurity by ammonium chloride crystals causes high internal stress (up to 4 GPa) in them, which manifests itself in the form of anomalous birefringence and leads to splitting, twinning, and cracking in NH₄Cl crystals.