KCl Single Crystals Research Articles

Bragg neutron diffraction studies on the crystalline solid solution KBrxCl1-x

Bragg neutron diffraction studies have been carried out on the crystalline solid solution system KBrxCl1-x for three different compositions, x=0.2, 0.4 and 0.8, and also for one of the end members, KCl single crystal. All the samples investigated were single-crystal samples, grown by melt method. The results in the case of crystalline solid solutions indicate enhancement of isotropic individual thermal parameters with a maximum corresponding to intermediate composition. The distortion factors (B') due to size effect for three different compositions were estimated following a method utilised for disordered binary alloys by Coyle and Gale (1955). These experimentally determined distortion factors for different compositions are compared with theoretical calculated factors based on two different models and the results are discussed. The variation of size effect factor or distortion factor with composition for this system is found to follow a parabolic trend.

Positron Annihilation in Mn2+‐Doped KCl Single Crystals

AbstractThe angular distribution of annihilation photons (ADAP) is measured in pure KCl single crystals and in that doped with Mn2+ impurities to concentrations of 60 and 250 ppm. In unannealed, impurity‐doped crystals, the intensity of the narrow component increases with the increase of the impurity concentration. The narrowing of the ADAP curves is explained by assuming trapping of positrons at impurity induced positive ion vacancies. On annealing, for 60 ppm impurity concentration, the intensity of the narrow component is greater than that for the unannealed sample of the same concentration, indicating dissolution of impurity–vacancy complexes, at elevated temperatures. For 250 ppm impurity concentration, comparing the results of the unannealed and annealed samples no great difference is found between the intensities of the narrow components indicating, that the dissolution of the impurity–vacancy complexes is not appreciable at higher concentrations, on heating.

Dielectric Properties of NaCl and KCl Single Crystals X-Irradiated under Different DC Fields

The dielectric constant, loss, and conductivity of NaCl and KCl crystals (as cleaved and quenched) subjected to X-irradiation in the presence of moderately large dc fields (≈10 kV/cm) are measured in the frequency range of 102 to 106 Hz at room temperature. The space charge effects observed from this study are discussed in the light of optical absorption data. Im Frequenzbereich von 102 bis 106 Hz werden bei Zimmertemperatur die Dielektrizitatskonstante, der Verlustfaktor und die Leitfahigkeit von NaCl- und KCl-Kristallen (frisch gespalten und getempert), die einer Rontgenbestrahlung in einem mittleren Gleichspannungsfeld (≈10 kV/cm) ausgesetzt werden, gemessen. Raumladungseffekte, die in dieser Untersuchung beobachtet werden, werden mit Blick auf die optischen Absorptionsdaten diskutiert.

Perfection of KCl Single Crystals Grown by the Czochralski Method

Perfection of KCl Single Crystals Grown by the Czochralski Method

Emission processes in the thermoluminescence of Li-Doped KCl single crystals

Emission processes in the thermoluminescence of Li-Doped KCl single crystals

Automated pulling of large alkali halide single crystals

A technique is described for pulling single crystals with simultaneous feeding of starting material to the melt; automatic control of the growth process is ensured by regulating the heater temperature in response to signals of a highly sensitive melt-level contact gauge. Growing crystal diameter d is preset by the ratio of the feed rate ṁ to pulling rate v p, axial growth rate being equal to v p. Crystal broadening from the seed up to the preset final diameter is automatically ensured by programming the ratio m ̇ v p . The stability of melt level in the crucible renders it possible to achieve a reproducible control over the shape of temperature field in the melt and in the growing crystal and hence, over the shape of interface. This technique was used for growing KCl single crystals up to 450 mm in diameter and 140 kg, and CsI:Na single crystals up to 300 mm in diameter and 115 kg. In the case of 300 mm dia. crystals a relative deviation of Δd d = ±1.5% was achieved over crystal length of 750 mm.

Optical Absorption of KCl Single Crystals in the Spectral Region from 1.1 to 7.0 eV

The reflectivity of KCl in the region from 1.1 to 6.2 eV has no structure and increases slightly with photon energy. Moreover, it depends little on the origin of the specimen. The optical density of KCl is small and increases linearly with photon energy in the region up to 5.5 eV. In this region, the optical density is almost independent of the thickness of the specimen and is therefore attributed to absorption at the surface. At 5.5 eV, however, the optical density rises steeply and depends on the thickness. However, the value extrapolated to zero thickness connects smoothly with the optical density below 5.5 eV. In KCl, the surface levels cover the band gap of the bulk. The levels which lie more than 4.0 eV below the vacuum level are occupied by electrons, and there seems to be a continuous and homogeneous distribution of the surface level.

Infrared and Raman spectra of ReO4-isolated in alkali halides

Single crystals of KCl, KBr, KI and RbI doped with up to about 0.1% ReO4- have been grown and studied by infrared and Raman methods. The spectra indicate that contrary to the implications of Zaporozhets and Pasechnyi (1979), the isolated perrhenate ion possesses Td symmetry in all cases.

Effect of high hydrostatic pressure on dislocation mobility in KCl single crystals

Effect of high hydrostatic pressure on dislocation mobility in KCl single crystals

Optical absorption and luminescence investigations of the precipitated phases ofEu2+in NaCl and KCl single crystals

A detailed study of the optical absorption and luminescence spectra associated with the precipitated phases of divalent europium in NaCl and KCl single crystals is reported. For the system NaCl-Eu${\mathrm{Cl}}_{2}$, three fluorescence bands peaking at 410, 439, and 485 nm were observed in crystals which were stored for six years at room temperature, without any previous heat treatment. The corresponding optical-absorption spectrum of these crystals consists of two broad bands peaking at 260 and 349 nm with a cubic crystalline field splitting 10Dq=9809 ${\mathrm{cm}}^{\ensuremath{-}1}$. After quenching the crystals from 600\ifmmode^\circ\else\textdegree\fi{}C, only one emission band peaking at 427 nm was observed and the corresponding optical-absorption spectrum consists also of two broad bands but now peaking at 240 and 347 nm with a 10Dq splitting of 12 849 ${\mathrm{cm}}^{\ensuremath{-}1}$. The emission band at 410 nm in the well-aged crystals was associated with the stable dihalide phase Eu${\mathrm{Cl}}_{2}$, while those peaking at 439 and 485 nm were ascribed to the metastable precipitated Eu${\mathrm{Cl}}_{2}$-like plate zones parallel to {111} and {310} planes of the matrix lattice, respectively. For the system KCl-Eu${\mathrm{Cl}}_{2}$, only one emission band peaking at 427 nm was observed in crystals stored at room temperature for five years, without any previous heat treatment. The corresponding optical-absorption spectrum of these well-aged crystals consists of two broad bands peaking at 244 and 349 nm with a 10Dq value of 12 331 ${\mathrm{cm}}^{\ensuremath{-}1}$. After quenching the samples, an emission band at 419 nm was observed and the corresponding optical-absorption spectrum was very similar to that observed before the quenching, although its 10Dq splitting was smaller (11 997 ${\mathrm{cm}}^{\ensuremath{-}1}$). In this case, the band peaking at 427 nm, observed in the well-aged crystals, has been tentatively associated with the metastable Suzuki phase of divalent europium in the potassium chloride host. The change in the absorption, excitation, and emission spectra associated with the different precipitated phases of ${\mathrm{Eu}}^{2+}$ in NaCl and KCl as a function of the annealing temperature is also reported.

Radiation‐Induced Emission of F2 Centres in KCl

AbstractAn emission has been observed in KCl single crystals subjected to 12 MeV electron pulses. The emission spectrum peaks at 1200 nm (1.03 eV) and has a temperature‐independent lifetime of 29.7 ns up to room temperature. Experiments with crystals previously irradiated to produce F and F2 centres showed that the emission mainly arose from direct excitation by the electron pulse of previously existing F2 centres. The lifetime data, but not the spectrum, are in good agreement with published data.

Defect kinetics in KCl single crystals

Defect kinetics in KCl single crystals

Thermal expansion measurements for estimating vacancy concentration in X-ray irradiated KCl single crystals

A sensitive capacitance technique is used for measuring changes in length (Δ l) of KCl single crystals with temperature in the region 30–300°C. These measurements have been taken on KCl in (i) as-cleaved (ii) X-ray irradiated (iii) quenched and X-ray irradiated conditions (X-ray irradiation was always done at room temperature (≈ 30°C). The linear coefficient of thermal expansion (α) of the as-cleaved sample is 40.8 × 10 -6°C -1. Variation of Δ l with temperature in X-ray irradiated crystal shows two regions: (a) 30–180°C where α is 48.1 × 10 -6°C -1, (b) 180–300°C where α is 40.4 × 10 -6°C -1. Similar behaviour is exhibited by quenched and later X-ray irradiated KCl the first region is up to 140°C, beyond which the second region takes over. From these data, concentration of vacancies in X-ray irradiated KCl at room temperature is calculated to be 3.4 × 10 17 cm -3 which is in fairly good agreement with the value obtained from F-band absorption measurements on the sample. An attempt has been made to understand these results.

Investigation of the radiation damage to a single crystal of KCl using the method of backward scattering and chaneling of hydrogen and helium ions

The method of channeling and backward scattering of H+ and He+ ions has been used to analyze the radiation defects in a single crystal of KCl when the crystal is irradiated with H+ and He+ ions with energies of 1 MeV. The position of the displaced atoms in the crystal lattice was determined and the value of the cross section for the formation of radiation defects and their rate of formation as a function of the radiation dose and orientation of the bombarded beam with respect to the 〈100〉 crystallographic axes of the crystal are found. The effect of an external electric field on the formation of the radiation defects was investigated. The effects of irradiation with H+ and He+ ions are compared with one another. It is shown that mechanisms connected with ionization and excitation of the crystal atoms make the main contribution to the formation of defects.

Optical investigation of divalent europium in the alkali chlorides and bromides

Detailed optical absorption data are reported for the divalent europium ion in NaCl, KCl, RbCl, KBr, RbBr, and KI single crystals at 300 and 77 K. Values of the oscillator strength are calculated for all the observed bands in the optical spectra at both temperatures. It is established that the optical spectra are well accounted for by a strong crystal field split 5d electron having a Coulomb interaction with the 4f6 core about one-half the free ion value. It is also shown that the measured 10 Dq cubic field splitting of the 4f6 5d configuration into its t2g and eg components is in accord with the expected order of the fields exerted by the different crystal media. In addition, calibration constants are reported for determining the Eu2+ concentration in KBr, RbBr, and KI single crystals by optical techniques, without destroying the sample.

Change in dislocation distribution of KCl single crystals during thermal cyclic annealing

AbstractThe change in dislocation distribution of KCl single crystals during thermal cyclic annealing was studied by etch pit method. The results obtained are summarized as follows.(1) In contrast to the case in Cu (KITAJIMA et al.; HASEGAWA et al.), the dislocation distribution in KCl crystals became non‐uniform with an increase in the cyclic annealing time, i.e., in the region near the surface, many sub‐boundaries were formed, but in the interior, the density of dislocations and sub‐boundaries decreased. The cyclic annealing is more effective in reducing the dislocation density than the isothermal annealing.(2) The longer the period of thermal cycle, the more effective in reducing the dislocation density.(3) The larger the temperature difference between the maximum and minimum during one cycle, the more effective in reducing the dislocation density.(4) In the Sr‐doped crystals, the thermal cyclic annealing was also effective in reducing the dislocation density within subgrains but sub‐boundary length per unit area slightly increased by the cyclic annealing.(5) When the samples were annealed under the atmosphere of Cl2, the dislocation density remarkably increased against our expectation, although the scattering centres had disappeared by this treatment.

K +3P-core excitons in potassium halides studied at low temperatures with high resolution

Reflection spectra of KF, KCl, KBr and KI single crystals have been measured at photon energies of approximately 20 eV with a bandwidth of 10 meV using synchrotron radiation in order to study fine structure and temperature dependence of the excitonic transitions associated with the K +3 p core level. The crystals were cleaved under ultrahigh vacuum and cooled down to 20 K. Information on energy positions, halfwidths and line shapes for the K +3 p-core excitons and their temperature dependence has been obtained. A new exciton predicted by the ligand field model was observed. For KI we evaluate an electron-hole exchange energy of only 30 (± 7) meV.

F-band absorption and thermoluminescence of KCl single crystals under DC field and X-ray irradiation

physica status solidi (a)Volume 52, Issue 2 p. K147-K150 Short Note F-band absorption and thermoluminescence of KCl single crystals under DC field and X-ray irradiation A. Subrahmanyam, A. Subrahmanyam Department of Physics, Indian Institue of Technology, KharagpurSearch for more papers by this authorK. V. Rao, K. V. Rao Department of Physics, Indian Institue of Technology, KharagpurSearch for more papers by this author A. Subrahmanyam, A. Subrahmanyam Department of Physics, Indian Institue of Technology, KharagpurSearch for more papers by this authorK. V. Rao, K. V. Rao Department of Physics, Indian Institue of Technology, KharagpurSearch for more papers by this author First published: 16 April 1979 https://doi.org/10.1002/pssa.2210520254Citations: 33AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume52, Issue216 April 1979Pages K147-K150 RelatedInformation

A Non-Destructive Method for Determining the Eu2+ Concentration in the Alkali Chlorides

Single crystals of NaCl, KCl and RbCl doped with divalent europium up to 600 p.p.m. were grown by the Czochralski technique. Taking advantage that the Eu2+ ion produces two optical absorption bands in these crystals, calibration constants for determining the Eu2+ concentration in the alkali chlorides by optical techniques are reported. Oscillator strengths of the absorption bands were calculated from the knowledge of the divalent europium concentration. In addition, the distribution coefficient of Eu2+ in NaCl, KCl and RbCl single crystals was determined by the use of this nondestructive method.

Epitaxial crystallization of polyoxymethylene during cationic polymerization of trioxane

AbstractEpitaxial crystallization of polyoxymethylene (POM) during cationic polymerization of trioxane in ethane dichloride was studied. Nascent POM crystals grew epitaxially on the surface of drawn, high‐molecular‐weight POM and on the (001) surface of KCl single crystals. Half‐hexagonal crystals several thousand angstroms in thickness were formed on these substrates. No discrete diffraction maximum could be observed in small‐angle x‐ray scattering patterns, but diffuse streaks were present on both the equator and the meridian of the pattern. These diffuse streaks are due to inhomogeneities in the nascent crystals. It is proposed that the crystals contain voids due to occlusion of reactive chain ends in the crystal. The optical diffraction pattern from a model made up of rectangles agreed qualitatively with the actual x‐ray pattern.