Deformation of doped NaCl crystals during uniaxial compression at temperatures of 4.2–293 K

The impurity weakening of crystalline NaCl:Mg and NaCl:Mn associated with purification of the matrix in a melt is demonstrated. This effect is manifested in a consistent change in the yield strength and mobility of dislocations. Its unusual temperature dependence is determined: in a number of cases weakening becomes greater as the temperature is lowered within the interval 293–4.2 K. A deviation in the elastic region of the stress-strain curves is observed to increase as the temperature is lowered. Plasticizing of crystalline NaCl is established: when the deformation temperature is lowered from 293 to 77 and 4.2 K the rate of rise in the yield strength of Cd²⁺ and Sr²⁺ doped samples is lower than that of undoped samples. An explanation for this fact is proposed. Fiz. Tverd. Tela (St. Petersburg) 39, 313–317 (February 1997) Deceased.     

Magnetoplastic effect in silicon: A search for new methods of controlling structure-sensitive properties of elemental semiconductors

The effect of static magnetic fields up to 1 T on the state of impurity point defects and the mobility of surface dislocation segments in doped (0.01–1.00 Ω cm) silicon has been considered. Long-lived (∼100 h) changes in the state of point defects have been revealed from the mobility of dislocations introduced after the magnetic-field treatment. The concentration dependence of the magnetoplastic effect in p-type silicon has been studied. A threshold impurity concentration of 10¹⁵ cm⁻³ has been found, below which the magneto-plastic effect has not been observed. The influence of magnetic-field pretreatment on the expectation times and activation barriers for dislocation depinning from stoppers and the effect of thermal preannealing on the magnetoplasticity in Si have been considered.     

Statistical description of the motion of dislocation kinks in a random field of impurities adsorbed by a dislocation

A model has been proposed for describing the influence of impurities adsorbed by dislocation cores on the mobility of dislocation kinks in materials with a high crystalline relief (Peierls barriers). The delay time spectrum of kinks at statistical fluctuations of the impurity density has been calculated for a sufficiently high energy of interaction between impurities and dislocations when the migration potential is not reduced to a random Gaussian potential. It has been shown that fluctuations in the impurity distribution substantially change the character of the migration of dislocation kinks due to the slow decrease in the probability of long delay times. The dependences of the position of the boundary of the dynamic phase transition to a sublinear drift of kinks x ∝ t^δ (δ σ 1) and the characteristics of the anomalous mobility on the physical parameters (stress, impurity concentration, experimental temperature, etc.) have been calculated.     

In situ investigation of the effect of a magnetic field on the mobility of dislocations in deformed KCl:Ca single crystals

This paper presents the results of an experimental investigation into the mobility of edge dislocations in KCl:Ca single crystals and the effect of a static magnetic field of 0.3 T on the dislocation mobility. The experiments on the effect of a magnetic field on the dislocation mobility were carried out with the use of a high-resolution (1 ms) method that permits in situ measurements of the sample dipole moment induced by the motion of charged dislocations as the crystal is being deformed. It is found that the starting stress is reduced in a magnetic field and the activation volume for overcoming of point defects by the dislocations is increased. It is further found that the magnetic field increases the rate of motion of the dislocations at the initial stage of deformation (to the point of dislocation multiplication) but has no effect on the mobility in the multiplication stage. Fiz. Tverd. Tela (St. Petersburg) 39, 630–633 (April 1997)     

Dislocations used to probe the defect state of an ionic crystal lattice excited by a pulsed magnetic field

This paper presents the results of an investigation into the effect of a pulsed magnetic field on the state of linear and point defects in ionic crystals. For different amplitudes (1–7 T) and pulse lengths (3×10⁻⁵ to 10² s) of the pulsed field the kinetics of the transformation of defects into a new state and their relaxation after the field is turned off are studied in the temperature range 77–400 K. It is found that the relaxation of the states of point defects is mainly through recombination, and the change of state of the dislocations and of the point defects contribute nonadditively to the change in the dislocation mobility. The exposure of the crystal to a magnetic field leads to an increase in the dislocation mobility when the sample is mechanically stressed and to a decrease in the dislocation displacement with a second field pulse. Fiz. Tverd. Tela (St. Petersburg) 39, 634–639 (April 1997)     

On the nature of the influence of an electric current on the magnetically stimulated microplasticity of Al single crystals

A large increase in dislocation mobility in Al single crystals in a static magnetic field in the absence of mechanical loading of the samples is observed when a dc electric current of low density (10⁵–10⁶ A/m²)is additionally passed through the samples. Apparently, the role of the current reduces to depinning of dislocations from strong pinning centers on the surface of the crystal as a result of surface electromigration of defects. This interpretation is supported by the fact that in samples whose surface is insulated by a layer of lacquer the passage of a current through the volume of the crystal does not change the ordinary dislocation mobility level in a magnetic field. It is hypothesized that surface electromigration of defects, which frees dislocations and unblocks dislocation sources, also plays a key role in the physical mechanism of the long-ago discovered macroplastification of metals upon the passage of an electric current through them. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 788–793 (25 May 1998)     

Dislocation dynamics in doped NaCl single crystals determined by pulsed NMR between RT and 300°C

The mean free path of mobile dislocations is measured by determination of the spin-lattice relaxation rate of deforming NaCl single crystals as a function of temperature and of the concentration of Ca⁺⁺ impurities. The latter may influence the magnitude of the mean free path but this depends to a large extent on the point defect configuration. The degree of association and the mobility of the point defects is studied by measuring the spin-lattice relaxation rate without deforming the samples. On the other hand the distribution of dislocations varies also with temperature and this affects the mobility of dislocations too. The work-hardening rate of the crystals is compared with the mean free path as a function of temperature and it is shown that both quantities have extremes under the influence of competitive mechanisms such as an enhanced thermal activation of dislocations at obstacles, an increasing mobility of point defects, and increasing number of intersections of mobile dislocations with dislocation dipoles.     

Static and dynamic hyperfine interactions of Mn and Co impurities in the weak ferromagnet ZrZn2

We report the nuclear orientation of near-stoichiometric samples of ZrZn₂ containing trace impurities of radioactive⁵⁴Mn and⁶⁰Co in the temperature range 6.5–60 mK and in applied fields between 0.2 and 5.7 T. Analysis of the resullts indicates that in both cases, the transition-element impurities occupy two sites (the Zr and Zn sites) with about equal probablities. In one site, most probably that of Zr, both impurities have positive hyperfine fields of +12.0 T and +3.8 T for Mn and Co, respectively; in the other site, the corresponding hyperfine fields are negative, with the values −6.0 T and −6.9 T. The dynamic hyperfine interaction of Mn in ZrZn₂ has also been studied using the thermal cyclic method with a weak thermal link, and was analyzed for the two relaxation times corresponding to the different lattice sites.     

Study of the local defect structure of CdTe-Ge crystals by microindentation

This paper demonstrates the effectiveness of the microindentation method as a way to monitor the quality of cadmium telluride crystals. Measurements of microhardness and the length of dislocation rays from the rosette around the indentation pit can clearly identify nonuniform distributions of structural defects, both along the direction of growth and along a diameter of a CdTe boule. The mobility of α dislocations is more sensitive to nonuniformities in the structure than the mobility of β dislocations and the microhardness. A qualitative correspondence is established between the microplasticity characteristics of CdTe:Ge and its germanium content: the hardness of the crystal is insensitive to changes in the Ge content in the range from 3×10¹⁶ to 1×10¹⁷ at/cm³, but increases sharply beginning at a concentration of ∼1×10¹⁷ at/cm³. The correlation between the value of the microhardness and the length of the dislocation rays from the rosette around the imprint of the indentor are analyzed. An estimate is obtained for the hardness of pure CdTe. Fiz. Tverd. Tela (St. Petersburg) 40, 264–268 (February 1998)     

HgSe:Fe—a mixed-valency system and the problem of the ground state

The dependence of the electron mobility on the iron impurity content N _Fe and temperature is studied for three variants of the ordering of Fe³⁺ ions in crystalline HgSe:Fe, a weakly correlated gas, states with near ordering like that in a strongly correlated Coulomb liquid, and long-range ordering. The electron mobilities owing to scattering on the correlated system of Fe³⁺ ions are determined. The temperature dependence of the mobility is analyzed for electron scattering on fluctuations in the charge density in a system of Fe²⁺-Fe³⁺ iron ions with mixed valency, and the correlation length is determined. It is shown that the ordering region for the Fe³⁺ ions encompasses only the first coordination sphere, i.e., near ordering in the position of the Fe³⁺ ions is established, as in a liquid. The coupling between the ordering of the Fe³⁺ ions and the formation of a correlation gap in the density of impurity d-states and its effect on the low-temperature behavior of the electron mobility in HgSe:Fe crystals are examined. Fiz. Tverd. Tela (St. Petersburg) 40, 425–432 (March 1998)     

Influence of temperature and strain on the amplitude-dependent internal friction of high-purity aluminum

The dislocation amplitude-dependent friction (ADIF) of high-purity (99.999%) polycrystalline aluminum is investigated in the temperature range 7–300K at vibrational strain amplitudes of 10⁻⁷–10⁻⁴ for samples in the annealed and deformed (by quasistatic, shock, and ultrasonic loading) states. The ADIF is a multistage effect in the indicated temperature and vibration amplitude ranges. Analysis of the amplitude-temperature spectra of the ADIF permits separation of components attributable to: interaction between dislocations, the interaction of dislocations with pinning points, and pure dislocation relaxation (the interaction of dislocations with the Peierls relief). ADIF is observed to depend nonmonotonically on the initial quasistatic strain determined by strain hardening and recovery processes. Fiz. Tverd. Tela (St. Petersburg) 40, 1839–1844 (October 1998)     

高剂量离子注入形成的非晶层重新结晶过程中杂质外扩散的物理模型

本文提出了一个杂质沉淀引起位错生成、位错-杂质相互作用、杂质原子沿晶粒间界快速扩散的模型,用以解释高剂量离子注入形成的非晶层在重新结晶的退火过程中杂质外扩散和缺陷运动现象。给出了在位错的合应力场的影响下杂质的扩散方程。以能量为80keV,剂量为10¹⁶cm^-2的Pb⁺注入Si(111)面为例,对扩散方程进行了数学物理处理,从而给出了根据实验测量推演表观扩散系数随时间变化及位错的合应力场对杂质的作用力的纵向分布的方法。实验测得的位错合应力场对杂质的作用系数α≈8.4×10^-28dyn·cm³,退火时间在5×10³sec至8.25×10³sec内,表观扩散系数D随时间的变化为一指数关系。 关键词：     

Luminescence properties of calcium-iodide crystals

The effect of the conditions of preparation, temperature, and the action of x rays on the luminescence properties of calcium-iodide scintillation crystals is investigated. On the basis of the results of a study of the spectral characteristics of CaI₂ and CaI₂:H₂ crystals for optical and x-ray excitation in the temperature range 90–400 K, also taking into account the results of a study of the luminescence properties of CaI₂ crystals activated by Cl⁻, Br⁻, OH⁻, and Ca²⁺ impurities, it is suggested that the 236-nm band observed in the excitation spectra of crystals of calcium iodide may be caused by an uncontrollable hydrogen impurity. The luminescence of these crystals with maximum at 395 nm is ascribed to radiative recombination of excitons trapped at H⁻ ions. Zh. Tekh. Fiz. 69, 135–136 (January 1999)     

Influence of divalent cationic impurities on plasticity of AgCl

The hardening effect of Mg²⁺, Ca²⁺, Sr²⁺, Cd²⁺ and Ba²⁺ impurities in polycrystalline AgCl was investigated. With exception of Mg²⁺ the hardening effect of the impurities decreases with increasing atomic number (atomic weight). The hardening effects of Mg²⁺ and Ca²⁺ are expressively stronger than those of the three remaining impurities. Approximately linear dependence of the stress at the beginning of plastic deformation on the impurity concentration was found. Possible causes of the different hardening effects of the divalent impurities are discussed.     

Kinetics of accumulation of vacancy complexes in dislocated silicon under 60Co γ-ray irradiation

Abstract

Radiation defect accumulation in ⁶⁰Co γ-ray-irradiated n-type Si single crystals (ρ=150ωcm) with various densities of dislocations (N_D = 1 × 10⁴ to 1 × 10⁷ cm ^?2) introduced at plastic deformation was studied. The temperature dependences of the Hall coefficient were measured. The probabilities of interaction of vacancies with oxygen, phosphorus atoms, and dislocation line elements were determined. It has been established that with the increase of N_D they can increase at the expense of complication of dislocation structure, decrease during formation of impurity atmosphere near dislocations and compensation of deformation fields, and they do not change if complex formation of vacancies with impurities occurs far from dislocations. Kinetics of A- and E-centre accumulation in the crystals containing dislocations with different impurity atmosphere was described.     

Electric stimulation of magnetoplasticity and magnetic hardening in crystals

The effect of electric field E on the magnetoplastic effect (MPE) has been investigated in NaCl crystals with different impurities, which provide either the plasticization of the samples in the magnetic field (positive MPE) or their magnetic hardening (negative MPE). The mobility of individual dislocations under the joint action of the magnetic and electric fields and the mechanical load on the crystals has been studied. The sharp electric stimulation of the MPE of both signs has been revealed, i.e., an increase or a decrease in the mean free path of dislocations that is roughly proportional to exp(±E/E ₀) at E ? E ₀ ～ 1–10 kV/m. In particular, in the negative-MPE NaCl(Pb) crystals, the accompanying electric field enhances the magnetic suppression of plasticity. The results are attributed to the electrically induced transformation of the additional part of the pinning impurity ions Me⁺⁺ to the magnetically active state of Me⁺ on the dislocations. The subsequent magnetic transformation of the structure of these pinning centers should lead to a sharper variation of the dislocation pinning force (either an increase or a decrease, depending on the MPE sign).     

Effect of isoelectronic impurities K<Superscript>+</Superscript> and I<Superscript>−</Superscript> on luminescence of CsBr:Eu<Superscript>2+</Superscript> crystals

We have investigated the photoluminescence (PL) and photostimulated luminescence (PSL) spectra at 300 K to study the effect of isoelectronic impurities K⁺ and I⁻ on the formation and energy structure of Eu²⁺-V_Cs isolated dipole centers and aggregate centers in the form of single crystals of CsEuBr₃ in CsBr:Eu²⁺ single crystals. We have shown that K⁺ and I⁻ impurities in a concentration of 5 mol% do not have a substantial effect on the energy spectrum of isolated dipole centers in CsBr:Eu²⁺ single crystals and the processes for the formation of such centers during growth of CsBr:Eu single crystals from the melt by the Bridgman method. We have established that in Cs_0.95K^0.05Br:Eu²⁺, more favorable conditions are realized for the formation of aggregate centers than in CsBr:Eu²⁺ and CsBr^0.95K^0.05Br:Eu²⁺ single crystals. So in order to improve the storage properties of phosphors based on CsBr:Eu²⁺, in particular for increasing the efficiency of PSL excitation, it is expedient to dope them with K⁺ impurity in a concentration up to 5 mol%. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 627–630, September–October, 2007.     

Radiation stabilization of U5+ in CaO matrix and its thermal stability: Electron paramagnetic resonance and thermally stimulated luminescence studies

Electron paramagnetic resonance (EPR) evidence is presented for the radiation stabilization of pentavalent uranium in CaO matrix. From the theoretical predictions ofg value for U⁵⁺ in axial symmetries, it was concluded that U⁵⁺ at Ca²⁺ site is associated with a second neighbour charge compensating Ca²⁺ vacancy. EPR measurements also revealed the presence of Mn²⁺, Mn⁴⁺ and Cu²⁺ impurities in the samples. The thermal stability of U⁵⁺ was investigated using EPR and thermally stimulated luminescence (TSL) techniques. The TSL and EPR studies on gamma irradiated uranium doped calcium oxide samples had shown that the intense glow peak at 540 K is associated with the reduction in the intensity of EPR signal of U⁵⁺ ion around this temperature. This peak is associated with the process U⁵⁺+hole→U^6+*→U⁶⁺+hv. The activation energy for this process was determined to be 1.4eV.     

Laser annealing of radiation defects in low disordered layers

Abstract

Carrier concentration and mobility dependences on the annealing temperature have been compared for the cases of thermal (10 min) and laser (8 ms) annealing of silicon, implanted with low doses of P⁺ ions. It was found that the recovery of concentration and mobility depended on the heating time in different ways. The laser annealing requires higher temperatures for mobility recovery then the thermal treatment. The same temperature shift was observed for increase of carrier concentration but only after doses less than 3.10¹²m^?2. When the doses exceeded 3.10¹² cm^?2 laser and thermal annealing resulted in equal electron concentrations providing the equality of heating temperatures. Annealing of disordered regions was accounted for the mobility recovery. The increase of electron concentration was explained as an instantaneous decay of defect-impurity complexes. To check the validity of the assumptions laser annealing of electron and light ions irradiated materials was investigated.     

Theoretical analysis of the impurity distribution in single-crystal silicon

Results are presented for the total energies calculated for oxygen and carbon impurities in silicon at T=0 K. The equilibrium positions of these point defects are determined at low (10⁻³–10⁻² at. %) concentrations. Fiz. Tverd. Tela (St. Petersburg) 39, 1384–1385 (August 1996)