Ionic conductivity studies in KCl–NaCl mixed crystals

Single crystals of KCl and a few compositions of KCl-NaCl mixed crystals were grown from melt by Kyropoulos technique. Ionic conductivity measurements have been carried in these crystals in the temperature range 100 to 400 °C. The activation energy for the migration of charge carriers have been calculated from the conductivity-temperature plots of these crystals and the results obtained were discussed.     

Thermoluminescence studies in KBrxI1–x mixed crystals

Thermoluminescence (TL) studies have been carried out in KBr, KI, and in different compositions of KBr_xI_1–x mixed crystals as a function of X-irradiation time. The TL glow peaks have been analysed and the trap depths and frequency factors have been calculated for different compositions. The complex TL peaks observed in these crystals were isolated by using thermal cleaning technique. The various glow peaks observed in these crystals were attributed to native impurities, first stage and second stage colour centers and the results have been discussed.     

Multi-stage work hardening in soft KCl crystals

In order to verify notions about the nature of the stage behaviour in KCl crystals the influence of purity and dimensions of KCl crystals on the stage behaviour of the workhardening curve τ(ϵ) has been studied. It is shown that in soft KCl crystals up to six stages of work hardening are observed. With increasing rigidity and decreasing sample dimensions (less than 2 mm² cross section) the number of observable stages is reduced to three. As work hardening builds up the extent of odd stages (I, III, V) grows and that of even stages (II, IV) falls. The dependence of 1/γ on strain ϵ (γ-activation “volume” of dislocation motion) for all the crystals studied is shown to replicate the τ(ϵ) curve. The rule of increasing the linear density of thermally surmountable obstacles on dislocations is the same for every pair of stages. This indicates that the nature of stages III and V is the same and caused by the activity of new slip systems oblique to the primarily active in stages II and IV, respectively.     

Gel growth and X-ray studies of single crystals in the mixed system KDP:ADP

Crystals of KDP and ADP and of the mixed system KDP:ADP are grown by gel technique resulting in good quality single crystals. The lattice parameters and densities of the mixed crystals show a linear dependence on composition in accordance to Vegard's Rule.     

Growth dislocations in zonal isomorphously mixed crystals

The orientation, distribution, and density of dislocations in isomorphously mixed potassium-rubidium biphthalate crystals composed of two zones with different concentrations of isomorphous rubidium impurity are experimentally studied. A model for the formation of growth dislocations in the external zone, which compensate internal heterometry-induced stresses at the interface between the zones, is proposed.     

Stage B work‐hardening of magnesium single crystals

The change in microstructure during tensile deformation of magnesium single crystals by basal slip was studied with electron backscatter diffraction in the scanning electron microscope. Two samples were plastically deformed up to shear strains of 0.37 and 1.28 belonging to work‐hardening stages A and B, respectively. The results show that the local misorientations resulting from rotations around the <10 0> axis strongly increase the work‐hardening coefficient in stage B. The mechanism of work‐hardening in stage B is discussed with respect to subgrain formation. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Luminescence studies on zeolite crystals

Observations and results on studies of photoluminescence in zeolites are reported. Excitation and emission spectra for natrolite, scolecite and thomsonite are illustrated. Peak positions in spectra are summarised in tabular forms. It is shown that principal emission band in natrolite and heulandite increases with increase in iron percentage in them. Absence of this situation in stilbite is explained in terms of Na⁺ or K⁺ centre killers. It is established that photoluminescence observed in the present case is due to de-alumination of zeolites under study.     

Thermoluminescence and optical absorption studies in γ-irradiated KClxBr1–x mixed crystals

Thermoluminescence (TL) and optical absorption measurements have been carried in γ-irradiated KCl, KBr and various compositions of KCl_xBr_1–x mixed crystals as a function of irradiation time and composition. The position of the main glow peak (high temperature peak) and F-band position are found to vary non-linearly with composition, showing a correlation between colour centers and TL. The TL peaks have been analysed by numerical fitting and the trap depths and frequency factors have been calculated for different compositions of the mixed crystals. The thermal ionisation energy of F-centers has been calculated for the mixed crystals and it is found to vary non-linearly with composition. The results obtained in mixed crystals have been discussed in terms of high disorder present in them.     

Work‐hardening characteristics of Zn‐Ti alloy single crystals

Shear stress – shear strain curves of 0.14 at.%Ti alloyed Zn single crystals were measured in compression at different temperatures and shear strain rates. The work‐hardening coefficient for basal slip increases with decreasing temperature and increasing shear strain rate. The work‐hardening characteristics are compared with those reported for Zn single crystals with different constituents and purities. It is discussed with respect to the interaction of dislocations with dislocations, vacancies, vacancy agglomerates and solute atoms. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Role of Z1 centres in radiation hardening of NaCl:Ba2+ crystals

Radiation hardening studies of undoped NaCl and NaCl crystals doped with barium have been carried out both in the as-grown state and after quenching them from 650°C. It is observed that the radiation hardening is more in doped crystals and the results are explained taking into consideration the role of Z₁-centres.     

Neutron studies of the structure and dynamics of Rb1 − x (NH4)xI mixed crystals

The structural and dynamical properties of the x-T phase diagram of the system of Rb_{1 ? x} (NH₄)_xI mixed crystals is of great interest, because such solid solutions are almost free of internal stresses due to almost equal ionic radii of ammonium and rubidium. The x-T phase diagram of Rb_{1 ? x} (NH₄)_xI is studied on samples with ammonium concentration ranging from 0.01 to 0.73 over the temperature range from 15 to 300 K by the methods of powder neutron diffraction and inelastic incoherent neutron scattering. The results obtained by powder neutron diffraction show that the α-β phase transition at low temperature is rather extended and occurs at the ammonium concentrations x = 0.50 and 0.66. The region of orientational state glass is determined by inelastic incoherent neutron scattering at the concentrations x = 0.29 and 0.40 at the temperature T = 20 K.     

Microhardness investigations on gel-grown barium cadmium oxalate mixed crystals

Microhardness characteristics of barium-cadmium oxalate crystals were undertaken using the indentation technique and the results there of are reported. The observed results were compared with the microhardness values of barium oxalate dihydrate and cadmium oxalate trihydrate crystals. The indentation induced cracks etched in 1N HCl reveal the surface of the dislocation pattern arround indentation mark. The mixed crystals show higher values of microhardness than the components barium oxalate dihydrate and cadmium oxalate trihydrate crystals.     

Coherent spinodal decomposition of equimolar mixed crystals of NaCl-KCl

Bulk density changes have been observed in equimolar mixed crystals of NaCl-KCl by flotation technique at RT. The results are accounted for on the basis of the theory of coherent spinodal transformation. The interdiffusion coefficient has been estimated from the kinetics of the transformation in the crystals.