KCl Crystals Research Articles

Brittle-to-ductile transition and slip band structure in ionic crystals

Abstract The interrelation between the brittle-to-ductile transition (BDT) and slip structure has been examined using NaCl and KCl crystals. In pre-cracked crystals of NaCl and KCl having a 〈100〉 axis, the fracture toughness K∗ic increases above 300 and 220 K, and the BDT occurs at 510 and 430 K respectively. Scale-like wavy lines are revealed ahead of a pre-crack on etched fracture faces of NaCl tested above 300 K. As the temperature increases, the step height and density of the lines are increased but the lines are more restricted near the pre-crack front. In NaCl and KCl crystals without pre-cracking, the critical resolved shear stress for {110} main slip is very low above 77 K, while that for {010} slip markedly increases as temperature decreases below 500 and 300 K respectively. In 〈100〉-uniaxial tests for non-pre-cracked NaCl crystals, the BDT takes place at around 380 and 480 K at strain rates of 5.5 × 10−6 and 5.5 × 10−5s−1 respectively. Above the BDT temperature, wavy slip lines are abundantly pr...

Carbonatite melt–CO 2 fluid inclusions in mantle xenoliths from Tenerife, Canary Islands: a story of trapping, immiscibility and fluid–rock interaction in the upper mantle

Three types of fluid inclusions have been identified in olivine porphyroclasts in the spinel harzburgite and lherzolite xenoliths from Tenerife: pure CO 2 (Type A); carbonate-rich CO 2–SO 2 mixtures (Type B); and polyphase inclusions dominated by silicate glass±fluid±sp±silicate±sulfide±carbonate (Type C). Type A inclusions commonly exhibit a “coating” (a few microns thick) consisting of an aggregate of a platy, hydrous Mg–Fe–Si phase, most likely talc, together with very small amounts of halite, dolomite and other phases. Larger crystals (e.g. (Na,K)Cl, dolomite, spinel, sulfide and phlogopite) may be found on either side of the “coating”, towards the wall of the host mineral or towards the inclusion center. These different fluids were formed through the immiscible separations and fluid–wall-rock reactions from a common, volatile-rich, siliceous, alkaline carbonatite melt infiltrating the upper mantle beneath the Tenerife. First, the original siliceous carbonatite melt is separated from a mixed CO 2–H 2O–NaCl fluid and a silicate/silicocarbonatite melt (preserved in Type A inclusions). The reaction of the carbonaceous silicate melt with the wall-rock minerals gave rise to large poikilitic orthopyroxene and clinopyroxene grains, and smaller neoblasts. During the metasomatic processes, the consumption of the silicate part of the melt produced carbonate-enriched Type B CO 2–SO 2 fluids which were trapped in exsolved orthopyroxene porphyroclasts. At the later stages, the interstitial silicate/silicocarbonatite fluids were trapped as Type C inclusions. At a temperature above 650 °C, the mixed CO 2–H 2O–NaCl fluid inside the Type A inclusions were separated into CO 2-rich fluid and H 2O–NaCl brine. At T<650 °C, the residual silicate melt reacted with the host olivine, forming a reaction rim or “coating” along the inclusion walls consisting of talc (or possibly serpentine) together with minute crystals of NaCl, KCl, carbonates and sulfides, leaving a residual CO 2 fluid. The homogenization temperatures of +2 to +25 °C obtained from the Type A CO 2 inclusions reflect the densities of the residual CO 2 after its reactions with the olivine host, and are unrelated to the initial fluid density or the external pressure at the time of trapping. The latter are restricted by the estimated crystallization temperatures of 1000–1200 °C, and the spinel lherzolite phase assemblage of the xenolith, which is 0.7–1.7 GPa.

Spectroscopic Studies of “Exciplex Tuning” for Dicyanoaurate(I) Ions Doped in Potassium Chloride Crystals

Photoluminescence and Raman results for single crystals of KCl doped with KAu(CN)2 with different Au content are presented and compared with results for pure KAu(CN)2 crystals. Photoluminescence spectra of the doped crystals show three major UV−vis bands that can be resolved by varying the excitation wavelength. Spectroscopic and computational evidence suggests the formation of Au−Au bonded excimers and exciplexes in this doped system. The excimer/exciplex luminescence bands can be tuned in a given crystal by site-selective excitation and their relative intensities tuned by varying the dopant concentration. Microsecond lifetimes were observed for the various luminescence bands, suggesting Au-centered phosphorescent emissions. Raman spectral analysis was used successfully to correlate with the luminescence bands observed in pure and doped crystals of [Au(CN)2-] and [Ag(CN)2-] systems. The Raman νCN bands corresponding to various sites of [Au(CN)2-]n and [Ag(CN)2-]n clusters in various crystals correlated well with the luminescence spectra, in terms of both the number of peaks and their relative frequencies. The results have illustrated interesting differences in the clustering of [Au(CN)2-] versus [Ag(CN)2-] ions in the host lattice. As the dopant level increases, the extent of metal−metal interactions increases due to larger oligomers or shorter metal−metal separation, in either case leading to decreased back-bonding and higher νCN frequencies. The νCN Raman frequencies in [Au(CN)2-]/KCl crystals with increasing doping level increased beyond the value for pure KAu(CN)2 crystals, presumably due to a shorter Au−Au distance in the highest doped crystal than the distance in the pure crystal. In contrast, increasing the doping level in [Ag(CN)2-]/KCl systems resulted in the appearance of νCN Raman peaks with correspondingly higher frequencies but the values remained lower than those for pure KAg(CN)2 crystals, as expected.

Impact attrition of particulate solids. Part 2: Experimental work

Single particle impact testing has been carried out to evaluate the attrition by chipping of ionic single crystals of MgO, NaCl and KCl, used as model materials having a semi-brittle failure mode. The results have verified the theoretical predictions presented in Part 1. The dimensionless attrition propensity parameter, η= ρv 2 lH/ K 2 c , is shown to account for the dependence of the material loss per impact on the material properties, impact velocity and particle size. The ‘chipping’ mechanism of impact attrition is further confirmed by the observations of the impact damage by the use of scanning electron microscopy. In addition, the influence of rigidity of target materials on attrition rate is also addressed.

Cathodoluminescence and Optically Active Regions of Intrinsic and Induced Defects in Eu2+-Doped KCl Crystals

Cathodoluminescence (CL) spectra and images of KCl : Eu 2+ have been measured between 80 and 300 K. The CL broad band observed in the spectrum has been assigned to the well known 4f 6 5d → 4f 7 electronic transition of the Eu 2+ ions and to the off center π luminescence (STE) modified by the F center absorption band (F center self-absorption). By studying the CL emissions at different temperatures it is found that the europium ions interfere the dynamics of the defect formation in KCl. In addition, the CL images have revealed the optically active zones in both the doped and pure samples.

Negatively charged Pb− ion produced by electrolytical colouration of KCl crystalscontaining Li+, Na+ and Rb+ ions

Electrolytic colouration has been undertaken for not only a KCl crystal containingPb2+ ions but also KCl crystals containing alkali impurity ions (Li+, Na+ and Rb+)besides Pb2 + ions. Absorption spectra of these electrolytically coloured crystalshave been studied, together with the emission spectra. Similar spectra wereobserved among these crystals. Eight weak absorption bands are observed in the290–700 nm region, while five intense bands are observed in the 200–290 nmregion. It is suggested that these bands arise from Pb− ions with tetragonal crystalfield symmetry. The energy-level assignment for these absorption bands is madeusing the energy-level diagram of the isoelectronic Bi0 atom with C4vcrystal field symmetry. It is suggested that an off-centre position effect of the Li+ion is observed in the KCl crystal codoped with Li+ ions. Broad emission bands at1530 and 1580 nm have been observed in electrolytically coloured KClcontaining Pb2 + ions and KCl containing Li+ and Pb2 + ions, respectively.

Striations in the KCl single crystals grown from aqueous solutions

Growth striations were always observed on the etched surfaces of KCl crystals grown from aqueous solutions doped with Pb. However, the origin of the striations is not known in the case of aqueous solution growth. In this work, it was studied how the width and period among the striations were influenced by the growth rate and concentration of the dopant Pb. The crystals were grown from the aqueous solutions doped with Pb (1/4000–1/1250 in molar fraction) by an evaporation method at pH=2.0. The average growth rates were changed from 24 to 115 μm/day by controlling the evaporation rate. It was found that both the width and period among the striations decreased with an increase of the average growth rate. However, the effects of the concentration of dopant Pb upon the width and period among the striations were not found within the concentration range examined.

Fast electron–hole plasma luminescence from track-cores in heavy-ion irradiated wide-band-gap crystals

Measurements of fast luminescence decays and time-resolved spectra reveal novel ultra-short-lived luminescence (several tens ps) in heavy-ion irradiated single crystals of LiF, NaF, NaCl, KCl, KBr, KI, RbI, CsCl, CsBr, CsI, α-alumina and MgO. The luminescence is characterized by its super-linear increase to excitation density, non-tailing decay, sample dependence and temperature-insensitive decay and yield. The luminescence can not be attributed to known excited species, but vigorous interaction among dense electron–hole pairs, i.e. plasma.

Type I FA (Rb +, Cs +) and II FA (Li +, Na +) tunable laser activities and donor-acceptor properties of O and O − at KCl (001) surface: first principle calculations

Type I F A (Rb +, Cs +) and II F A (Li +, Na +) tunable laser activities, adsorptivity and donor-acceptor properties of O and O − adsorbates at the flat surface of KCl crystal were investigated using an embedded cluster model and ab initio methods of molecular electronic structure calculations. Ion clusters were embedded in a simulated Coulomb field that closely approximates the Madelung field of the host surface, and the nearest neighbor ions to the defect site were allowed to relax to equilibrium. Based on the calculated Stokes shifted optical transition bands, F A tunable laser activities were found to be inversely proportional to the size of the dopant cation (Li +, Na +, Rb +, Cs +) relative to the host cation (K +). This relation was explained in terms of the axial perturbation of the impurity cation. The probability of orientational bleaching attributed to the RES saddle point ion configuration along the 〈110〉 axis was found to be inversely proportional to the size of the dopant cation, with activation energy barriers of ca. 0.44–3.34 eV. Surface relaxation energies of type II F A centers were more important than those of type I F A centers. In terms of defect formation energies, the products of type II F A center imperfection were more stable than those of type I F A. The difference between F or F A band energies and exciton bands depended almost exclusively on the size of the positive ion species. As far as the adsorptivity of O and O − is concerned, the results confirm that surface imperfection enhances the adsorption energies by ca. 4.38–16.37 eV. O and O − penetrate through the defect-containing surface. The energy gap between the adsorbate and the defect containing surface and the donor-acceptor property of adsorbate play the dominant role in the course of adsorbate substrate interactions and the results were explained in terms of electrostatic potential curves and Mulliken population analysis.

Hyperfine interactions and lattice distortion of the F center in KCl, NaCl and LiCl crystals

Detailed embedded-cluster quantum-chemistry (ROHF, UHF and UMP2) calculations of hyperfine interactions for the F center in KCl, NaCl and LiCl are presented. Our values for the isotropic hyperfine interaction show a good general agreement with experiments. We show that a careful treatment of the lattice environment, local lattice distortion, spin polarization and correlation are important for this good agreement.

Study of Ag −- and Ag 0-type centers in X- and γ-ray irradiated NaCl:Ag +, KCl:Ag + and NaCl:Ag + + Ca 2+ crystals

Creation of Ag − and Ag 0 centers by irradiation with ionizing radiations has been investigated using NaCl and KCl crystals containing various concentrations of Ag + ions and using Ca 2+-codoped NaCl:Ag + and KCl:Ag + crystals. From the absorption spectra, it is observed that Ag − center perturbed by Ca 2+ ion is also created besides the Ag − and Ag 0 centers. It is confirmed that Ag − and Ag 0 centers increase with increasing the concentration of doped Ag + ions. It is suggested that there are two kinds of Ag 0 cv a centers (i.e. Ag 0 accompanied by vacancy at the nearest neighbor) with different site symmetries depending on the location of vacancy.

DIFFUSION OF Tl+ IONS THROUGH THE INTERFACE OF SOLID NaCl, KCl OR RbCl AND LIQUID TlCl

The diffusion phenomena of thallous ions ( Tl + ions) through solid-liquid interface of liquid Tl + ions diffusion source and sodium chloride (NaCl) , potassium chloride (KCl) or rubidium chloride (RbCl) single crystals are studied by optical method. The characterisic absorption peaks of Tl + center in NaCl, KCl or RbCl single crystals were used as the tracer for measurements and the diffusion constants are evaluated at various temperatures. The results show that the diffusion constant of solid-liquid interface is about 103 times larger than that of solid-solid interface of KCl and TlCl .

Maximum channel pressure of a nanosecond pulsed anode discharge in a KCl crystal

The breakdown channel pressure is estimated for the initial stage of breakdown of a KCl crystal using experimental data on the fracture of KCl crystals upon anode pulsed discharges, the known strength of this crystal, and solutions of the corresponding static boundary‐value problem of the anisotropic theory of elasticity.

Inclusion of Mother Liquor inside KCl Crystals in a Continuous MSMPR Crystallizer.

The crystal size distribution (CSD) and crystal purity of potassium chloride (KCl) have been measured in an MSMPR crystallizer by using two different impellers. A small amount of sodium chloride (NaCl) was added as an impurity tracer in order to measure the inclusion ratio of mother liquor inside KCl crystals. The effects of mixing, residence time, growth rate and crystal size of KCl on the inclusion of mother liquor were investigated. The crystal growth rate and nucleation rate were determined from the population density balance theory. The attrition of crystals changed round shape of the crystal and affected significantly the inclusion of mother liquor in the crystals. The roundness of KCl crystals was proposed as a new factor to take the attrition effects into consideration. An empirical relationship between the inclusion of mother liquor and the operating variables was obtained.

The colouration by 60 Co-gamma rays of NaCl and KCl crystals doped with europium ions

Pure and europium doped NaCl and KCl crystals have been irradiated with 60 Co gamma rays and with ultraviolet light. The dose was 10 v kGy and temperatures during irradiation were ambient and liquid nitrogen. The effects of irradiation are determined using optical absorption and thermoluminescence. The role of the europium dopant is compared for the two materials. Factors investigated include the temperature of irradiation, the concentration of the dopant and the state of impurity aggregation and precipitation. A link is indicated between impurity precipitates and UV stimulated thermoluminescence.

The photoacoustic effect and non-radiative transitions OF F-centers in alkali halides

The common photoacoustic spectrum (PAS) is wider than the optical absorption spectrum in KCl crystals. A photoacoustic experiment was performed with a solid KCl sample that was additively colored according to the Van Doorn technique. The sample had about 10 17 v [F/cm 3 ]. It was determined that the PAS is composed of many bands of the F and aggregate centers. It is explained here, using the configuration coordinate model, that the photoacoustic effect in alkali halides with F-centers shows experimental broadening of the photoacoustic band relative to the F -band. Furthermore, experimental data is added resolving the photoacoustic bands of the agglomerates and also the bands of higher excited states of the F-center. Finally, assuming a configuration coordinate model and the F-centers as sources of heat, an estimation is made for the increase of the sample temperature.

Improved embedded molecular cluster model

AbstractWe demonstrate that boundary effects (i.e., displacements of the cluster boundary atoms from their lattice sites and the difference between effective charges of the perfect crystal atoms and those of the cluster atoms in the case of a cluster with no point defect in it) in an embedded molecular cluster (EMC) model can be radically reduced. A new embedding scheme is proposed. It includes search for the structural elements (SE) of which perfect crystal is composed, use of corresponding to these SE expression for the total energy, and application of the degree of localization of equations consistent with the wave functions of the cluster. To get equations for the cluster wave functions, the problem of varied subsystem in the field of the frozen remaining part of the whole electron system” is investigated in the framework of a one‐electron approximation. The consideration is general for every task of this type. Homogeneous equations resulting directly from variation of the total energy expression are obtained and transformed to the eigenvalue problem equations. Orthogonality constraints are not imposed during variation. A particular case of the equations describing mutually orthogonal one‐electron wave functions of the cluster staying nonorthogonal to those of the remaining crystal is found. A proposed embedding scheme is realized in the CLUSTER code based on the calculation scheme of the semiempirical INDO method. Boundary effects both in the standard (cluster in the field of the infinite lattice of nonpoint spherical charges) and new embedding scheme are investigated, calculating the clusters of LiF, MgO, NaCl, KCl, and AgCl crystals. Significant reduction of the boundary effects in the new embedding scheme is achieved. Reasons for the boundary effects are discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Optical Properties of Single Micron-Sized ZnO Particles Embedded in Alkali Halide Crystals Studied by Cathodoluminescence

In order to investigate optical properties of single micron-sized ZnO particles embedded in alkali halide (KCl) crystal, cathodoluminescence (CL) measurements at liquid helium temperature have been performed. In contrast to the case for pellet of ZnO powder, CL spectra of the single ZnO particles exhibit intense ultraviolet (UV) luminescence and no green emission due to oxygen vacancies, which ensures higher quality of the ZnO particles in the KCl crystal compared with that of the ZnO powder. The CL images of the single particles reveal several bright spots. The results indicate that radiative recombination of the excitons effectively occurs at specific areas in the surface of the single particle.

Optical Properties of Single Micron-Sized ZnO Particles Embedded in Alkali Halide Crystals Studied by Cathodoluminescence

In order to investigate optical properties of single micron-sized ZnO particles embedded in alkali halide (KCl) crystal, cathodoluminescence (CL) measurements at liquid helium temperature have been performed. In contrast to the case for pellet of ZnO powder, CL spectra of the single ZnO particles exhibit intense ultraviolet (UV) luminescence and no green emission due to oxygen vacancies, which ensures higher quality of the ZnO particles in the KCl crystal compared with that of the ZnO powder. The CL images of the single particles reveal several bright spots. The results indicate that radiative recombination of the excitons effectively occurs at specific areas in the surface of the single particle.

FA(Ga+,In+,Tl+) tunable laser activity and interaction of halogen atoms (F,Cl,Br,I,At) at the () surface of KCl crystal: ab initio calculations

Abstract An attempt has been made to examine F A (Ga + ,In + ,Tl + ) tunable laser activity and adsorptivity of halogen atoms (F,Cl,Br,I,At) at the (0 0 1) surface of KCl crystal using an embedded cluster model, CIS and density functional theory calculations with effective core potentials. The ion clusters were embedded in a simulated Coulomb field that closely approximates the Madelung field at the host surface. The nearest neighbor ions to the defect site were then allowed to relax to equilibrium. Based on the calculated strength of electron–phonon coupling and Stokes-shifted optical transition bands, The F A (Tl + ) center was found to be the most laser active in agreement with the experimental observation that the optical emissions of F A (In + ) and F A (Ga + ) centers were strongly quenched. The disappearance of the anisotropy and np splitting observed in the absorption of F A (Ga + ,In + ,Tl + ) centers were monotonically increasing functions of the size of the impurity cation. The F A (Ga + ,In + ,Tl + ) defect formation energies followed the order F A (Ga + )> F A (In + )> F A (Tl + ). The Glasner–Tompkins empirical relationship between the principal optical absorption of F centers in solids and the fundamental absorption of the host crystal was generalized to include the positive ion species. As far as the adsorptivity of the halogen atoms is concerned, the F and F A (In + ,Tl + ) centers were found to change the nature of adsorption from physical adsorption to chemical adsorption. The adsorption energies were monotonically increasing functions of the electronegativity of the halogen and the amount of charge transferred from the defect-free surface. The calculated adsorption energies were explainable in terms of the electron affinity, the effective nuclear charge and the electrostatic potentials at the surface. The spin pairing mechanism played the dominant role in the course of adsorbate–substrate interactions and the KCl defect-free surface can be made semiconducting by F or F A (In + ,Tl + ) surface imperfections.