KCl Single Crystals Research Articles

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 .

Gain-Narrowed Light Emission from Self-organized Organic Microdots

Organic microdots were self-organized by vapor deposition of emissive distyrylbenzene derivative molecules onto a cleaved surface of a KCl single crystal. When the deposition amounts were changed at an elevated substrate temperature, the microdot diameters were controlled from the submicrometer scale up to larger than 10 μm. Under optical pumping using a pulse laser, the microdots encapsulated in an MgF2 layer exhibited amplified spontaneous emission depending on the microdot size. While the spontaneous fluorescence band of the microdots smaller than the cutoff diameter of around 8 μm never collapsed even at high excitation energy, those beyond this size exhibited a gain-narrowed emission peak above a certain threshold energy.

Opacity of KCl single crystal shocked above the transition pressure

Strong absorption of light by shock-transformed KCl (potassium chloride) single crystal has been used for measurement of electrical conductivity of its high-pressure B2 phase. The obtained conductivity values allow the determination of the width W of the gap between the valence and the conduction bands and its dependence W=W0(1−bε) on the compressive strain ε. The values of the gap width W0=0.49±0.06 eV and of the parameter b=1.4±0.4 lead to the conclusion that KCl in its high-pressure modification is a semiconductor.

The structure of NaCl(1 0 0) and KCl(1 0 0) single crystal surfaces: a tensor low energy electron diffraction analysis

Relaxation and rumpling of the (1 0 0) surfaces of NaCl and KCl single crystals were investigated by means of low energy electron diffraction (LEED). For primary currents in the range of 5 nA, sharp diffraction patterns of (1×1) symmetry were measured in the temperature range between 20 and 295 K. Under these conditions, neither charging effects nor electron-induced surface damage were observed. The temperature dependence of the peak intensities is described by a surface Debye temperature of 174±3 K for NaCl and 146±10 K for KCl, respectively. From the sequence of diffraction patterns measured in the energy range between about 60 and 300 eV, intensity versus electron energy curves ( I( V) curves) were obtained for several diffraction peaks, and analyzed with the tensor LEED approach. Structural as well as non-structural parameters were varied systematically. According to the LEED analysis, the distance between first and second layer of NaCl is contracted by 1.4(7)% relative to the bulk value, and the chloride ions in the first layer are lifted by 0.07(3) Å while the sodium ions are shifted towards the bulk by the same amount. The second and third layer show almost no rumpling and layer distances close to the bulk value. For KCl, the spacing between the top layers is identical to the bulk value within the error bars. The cations of the first layer are relaxed towards the bulk by only 0.03(5) Å and the anions by the same amount outwards. For both substrates, the refined final structures were characterized by Pendry R-factors of 0.13.

Amplitude dependent internal friction during plastic deformation of KCl doped with KBr, KI, or SrCl2

Flow stress decreases by superimposition of ultrasonic oscillatory stress during plastic deformation. The amplitude dependent internal friction is investigated together with the stress decrement due to the superimposition of oscillation during the plastic deformation of KCl single crystals doped with KBr, KI or SrCl2. The relation between the amplitude dependent internal friction and the stress decrement is divided into three regions for KCI doped with KBr or KI. The internal friction is proportional to the stress decrement in the first region up to the first bending point at the lower stress amplitude. The stress decrement at the first bending point is proportional to the square root of KBr or KI concentration. The internal friction of KCl–SrCl2has the amplitude independent part. The stress decrement at the onset of increasing of internal friction is independent of SrCl2concentration. The amplitude dependent internal friction of KCl–KBr and KCl–KI consists of the part due to the impurity and that due to forest dislocation. The amplitude dependent internal friction of KCl–SrCl2is only due to the forest dislocation.

Interaction between a dislocation and various divalent impurity in KCl single crystals for the Fleischer's model taking account of the Friedel relation

The interaction between a dislocation and the impurity in KCl : Mg2+ (0.035 mol% in the melt), KCl : Ca2+ (0.035 and 0.065 mol% in the melt) and KCl : Ba2+ (0.050 and 0.065 mol% in the melt) was investigated from the strain-rate cycling test during the Blaha effect measurement. This was carried out at 77–254 K. As a result, it was found that the Fleischer's model taking account of the Friedel relation seems to be suitable for KCl : Ca2+ and KCl : Ba2+. However, it was not appropriate for KCl : Mg2+. Furthermore, the values of Tc, ΔH(Tc) and ΔG0 were obtained for the specimens. Tc is the critical temperature at which effective stress is zero. ΔH(Tc) and ΔG0 are the enthalpy and the Gibbs free energy of activation for the breakaway of the dislocation from the impurity, respectively. ΔH(Tc) was almost the same for the specimens except KCl : Mg2+. ΔG0 increased with increasing the divalent cation size. In addition, the tetragonality around the divalent ion-positive ion vacancy pair was estimated on the basis of ΔG0 for the each specimen.

Charged dislocations and plasto-electric effect in ionic crystals

The electric charges on the edge dislocations in KCl single crystals doped with divalent cation impurities were determined as a function of impurity concentration and temperature. This is then used to determine the density of mobile dislocations in compression, strain rate cycling, stress relaxation, latent hardening and the Bauschinger effect by using the plasto-electric effect. Some other plasto-electric, electro-plastic and magneto-plastic effects are also discussed.

Effect of post-deformation ageing on the recrystallization of KCl-SrCl2 crystals

Room-temperature recrystallization of KCl single crystals, both pure and doped with 0.02 and 0.06 wt % Sr, deformed preliminarily at 250°C is studied. It is found that annealing of the original single crystals at 650°C results in the precipitation of the SrCl2 phase from the solid solution. X-ray diffraction studies reveal that the deformed crystals undergo ageing at room temperature, which is accompanied by a change in the phase composition. In the first place, particles of the KSr2Cl5 phase are formed instead of the phase SrCl2 observed in the original and deformed crystals. These particles, which are located at the boundaries of growing recrystallized grains (twins of the original single crystal) occupying not more than 8% of the volume, impede the motion of grain boundaries and hamper further recrystallization. Second, it is shown that post-deformation ageing occurring in the remaining 92% of the deformed crystal region that has not undergone recrystallization lends stability to the strain-hardened state of alkali halide crystals over a period of at least two years at room temperature.

Softening of ionic crystals as a result of a change in the spin states of structural defects under paramagnetic resonance conditions

The purpose of this work was to investigate the plastic properties of Ca-or Eu-doped NaCl and KCl single crystals in crossed constant and microwave magnetic waves under paramagnetic resonance conditions. It was found that when the photon energy of the microwave field equals the Zeeman splitting of the electronic spin sublevels, resonance softening of the crystals, manifested as an increase in the free path of individual dislocations and the macroplastic flow velocity as well as a decrease of the microhardness of the crystals, is observed. It was established that metastable Ca-and Eu-impurity complexes, which are also sensitive to the constant magnetic field in the absence of the microwave field, as well as complexes formed by dislocations and point defects are responsible for resonance softening.

Natural electron oscillations in granular indium films deposited on rough surfaces of NaCl and KCl single crystals

Two plasma resonance bands were simultaneously observed in granular indium films deposited on rough surfaces of NaCl and KCl single crystals; one of them is caused by a combined action of the light-wave field and of the field created by the dipole grains, and the other, by the light-wave field alone with the frequency of natural electron oscillations ω0 in the grains. The indium plasma frequency, calculated from the measured frequencies ω0 and known dielectric constants of NaCl and KCl, agrees well with the known plasma frequency of bulk indium. An anisotropy in the plasma resonance band of granular indium films deposited on a rough NaCl surface was found and interpreted.

Plasma resonance in granular gallium films deposited on rough NACl and KCl single-crystal surfaces

Granular gallium films deposited in high vacuum on the rough surfaces of NaCl and KCl single crystals maintained at 400°C consist of two layers, in which two resonance bands are excited simultaneously. In isolated grains of the upper layer, a band at the normal electron oscillation frequency ω0 is excited. As a result of supercooling, the grains are in the liquid state. The gallium plasma frequency calculated from the measured ω0 and dielectric constants of NaCl and KCl coincides with that obtained by other authors by metallooptic methods. In gallium deposited on room-temperature substrates, only one resonance band is excited, with the interband absorption band superposed on its low-frequency edge.

Mass-Spectrometric Study of the Temperature Variation in the Dimer-to-Monomer Ratio in the Free-Surface Vaporization Fluxes from Alkali Halide Single Crystals

A mass-spectrometric method is used to investigate the kinetics of the vaporization of LiF (970–1070 K), NaCl (722–889 K), KCl (780–900 K), KBr (724–918 K), and CsI (656–838 K) single crystals. A dimer-to-monomer ratio, JD/JM, in the fluxes vaporizing from free surfaces of these crystals are calculated, using the currents of M+, MX+, and M2X+ ions formed via electron impact ionization of the molecules MX and M2X2 (M is the alkali atom; X is the halogen). It is found that the dimer-to-monomer ratio increases with temperature at a continually increasing rate in the LiF and NaCl cases. In the KCl, KBr, and CsI cases, this rate passes through a maximum. Such a specific temperature variation in JD/JM is discussed through the analysis of proposed mechanisms of dimer formation in light of the terrace–ledge–kink and surface charge models.

Natural electron oscillations in granular aluminum films deposited on rough surfaces of NaCl and KCl single crystals

Natural electron oscillations in granular aluminum films deposited on rough surfaces of NaCl and KCl single crystals

Natural electron oscillations in Te granules deposited on rough surfaces

Granular tellurium films deposited on rough surfaces of NaCl and KCl single crystals heated to 150 °C consist of two layers in each of which a resonance band is excited simultaneously. A band with frequency ω0 of natural electron oscillations is excited in isolated granules of the upper layer. The plasma frequency of bulk tellurium is calculated from the measured values of ω0 and the known permittivities of NaCl and KCl.

Luminescent Homoatomic Exciplexes in Dicyanoargentate(I) Ions Doped in Alkali Halide Crystals. 2. “Exciplex Tuning” by Varying the Dopant Concentration

The dependence of the dicyanoargentate(I) luminescence on the dopant concentration in [Ag(CN)2-]/KCl single crystals is reported. Three crystals with different Ag content have been studied. The photoluminescence spectrum of the doped crystal that has the lowest silver content (0.17%) is dominated by a high-energy band at ∼295 nm, while the spectrum with the highest silver content (4.3%) is dominated by a low-energy luminescence band at ∼400 nm. The crystal with an intermediate Ag content (2.7%) shows strong emissions from both the high-energy and low-energy bands. Time-resolved luminescence measurements indicate that the excitation energy is transferred between different [Ag(CN)2-]n oligomers and, thus, leads to the tunable emission observed in the [Ag(CN)2-]/KCl system. The mechanisms of the radiative and nonradiative processes have been described by a kinetic model that describes the experimental lifetime and time-resolved data.

Optically stimulated luminescence in KCl:Cu x-irradiated at room temperature

Optically stimulated luminescence (OSL) has been observed in single crystals of KCl:Cu x-irradiated at room temperature. It is shown that electrons are liberated from anion sites during the OSL process. The OSL predominantly involves emission due to radiative transition (d↔s) of monovalent copper ions present in the lattice. The OSL emission shows a strong temperature dependence indicating a thermally assisted process. Electron-hole recombination followed by energy transfer to the Cu activator is suggested as a possible OSL mechanism in KCl:Cu. Preliminary results of OSL in KBr:Cu are also presented.

Recrystallization of pure and strontium-doped KCl crystals

The kinetics of microstructure transformations are studied during annealing of deformed single crystals of KCl and KCl:0.05wt %Sr2+ at temperatures of (0.35–0.55)T m (where T m is the melting temperature) and during storage at room temperature. The effect of deformation rates ranging from 0.01 mm/min to 0.1 mm/min at a deformation temperature T d=0.5T m on the crystal structure and on the recrystallization kinetics is noted. It is found experimentally that the incubation period for static recrystallization in single-crystal KCl:0.05wt%Sr2+ is shortened and recrystallization takes place at room temperature after deformation in this temperature range. Here, during the new recrystallization grains have a twinned orientation with respect to the initial single crystal during the first stage and to the subgrains of the deformed crystal. As the annealing temperature is raised, the stage in which twins grow in KCl:0.05wt%Sr2+ crystals is shortened and it is displaced by recrystallization through migration of high-angle grain boundaries of the common type. Deformation conditions which ensure prolonged (at least three months) stability of the post-deformation hardening of single crystals are found experimentally for Sr2+-doped deformed single crystals.

Build-up of F and M color centers in KCl single crystals under combined electron and proton irradiation

The F and M color-center build-up kinetics in KCl crystals under combined irradiation with electrons of energy 15 and 100 keV and 100-keV protons have been studied in the flux range of 1013–1015 cm−2 and at a flux density of 3×1011 cm−2 s−1. It is shown that consecutive irradiation with electrons and protons produces results not obtainable under electron or proton irradiation alone.

Plasma resonance of granular indium films deposited on rough surfaces of NaCl and KCl single crystals

Granular silver films deposited on rough NaCl and KCl single-crystal surfaces exhibit, besides the low-frequency plasma-resonance band induced by the light-wave field and the field generated by the grain dipoles, a second, high-frequency plasma-resonance band, which is excited only by the light-wave field at the frequency ω0 of the natural electron vibrations in the grains. The dielectric constant due to interband transitions was calculated from the known plasma frequency and the dielectric constant of the medium surrounding thegrains, the plasma frequency ωp of the granular films, and the measured frequency of the maximum of surface plasmon vibrations in solid films. The results obtained agree with the data quoted by other authors.

Epitaxial structuring of blue light-emitting p-phenylene oligomers

Epitaxial structuring of blue light-emitting molecules, p-phenylene oligomers (p-nP, n=3,4,5,6), was investigated in thin crystals vapor deposited on the (001) surface of a KCl single crystal. Their molecular orientation and morphology changed depending on the molecular length and substrate temperatures during deposition. As the length of p-nP was longer and the substrate temperature was lower, the orientation of the molecular axis changed from standing to lying on the KCl surface due to an increase of molecule–substrate interactions. p-terphenyl (3P) hardly adsorbed on the KCl (001) surface, but a portion of the standing molecules stuck along the step edge of KCl and formed a walllike structure. Long needlelike crystals of p-hexaphenyl (6P) epitaxially grew in two orthogonal KCl [110] directions taking lying orientation even at a higher substrate temperature. In these epitaxial needles, the transition dipoles parallel to the molecular axis gave rise to blue fluorescence sharply polarized along the KCl [110] directions.