Search

Single crystals of KC1 containing sulfate ions have exhibited a large number of IR absorption peaks unless the crystals also contained an excess of divalent cations, in which case the spectra consist chiefly of 3 prominent absorban ces. This paper reports observations on crystals where the divalent cation concentration was low enough so the spectra were complicated. Progress was made in accounting for the peaks observed. A crystal-to-melt distribution ratio for sulfate ions is reported which makes it convenient to estimate the sulfate concentration for a crystal grown from a melt of known composition. Since sulfate ions bear a double charge, one expects their incorporation in an alkali halide crystal to be accompanied by the formation of negative ion vacancies. If such is the case, some pro nounced effects upon the behavior of F centers may result. Experiments with crystals contain ing sulfate ions which were additively colored. The sulfate ions were reduced to other divalent anions (e.g. peroxide) by the coloration process; these anions then markedly affect the bleaching of F centers. (Author), Report on A Magnetic Study of Color Centers in Alkali Halides.

The real part of the dielectric constant in crystalline V2O5 has been measured in the temperature range 80K to 200K. It rises from about 5, at low temperature, to about 9 in a narrow temperature range which depends upon frequency. The ac conductivity exceeds the dc conductivity by a measurable amount at low temperature, because of the contribution of relaxation. The crystal behaves approximately as a Debye dielectric. The relaxation time was found as a function of temperature. Two models for dipolar centers are proposed and discussed. (Author), Report on Electrochemistry of Primary Oxide Electrodes.

The behavior of V2O5 single crystals, grown from the melt, during cathodic polarization and recovery, was investigated. The dependence of potential upon pH showed that the only plausible reduction product was a solid oxide or oxyhydroxide, polarization being due to the formation of a solid solution. In the pH range 2.0 - 5.5, the curve of electrode potential vs. time during both polarization and recovery was accurately predicted by an equation, already applied to MnO2, derived from the assumption that the product is removed from the surface by diffusion into the electrode. Using tritium as a tracer, it was shown that hydrogen is incorporated in the electrode during discharge at pH 4.7. The activation energy for diffusion was found to be 6.7 kcal/mole, which is consistent with bipolar diffusion of protons and electrons. (Author)

A summary of research performed under Contract N onr 1286(05) is given together with lists of Technical Reports and publications. (Author)

KCl single crystals, homogeneously doped with PbCl2, were analyzed for lead by the dithizone method, and the optical absorbance at 273 millimicrons was determined. The absorbance at 273 millimicrons in samples of a given lead concentration depended on original purity of the KCl, the atmosphere under which the crystal was grown, and the thermal treatment prior to measurement. The oscillator strength was found to be 0.11 plus or minus 0.02 in crystals of highest purity, grown under dry HCl or argon, and rapidly quenched from 600C. This agrees with the value reported by Sibley, Sonder, and Butler. When reagent grade KCl was used, or the atmosphere was air, the average oscillator strength found was 0.086, which is close to the value reported by Kaifu. (Author)

A method for the growth of single crystals of V2O5, as thin plates, is described. The cathodic polarization and recovery in a buffer solution saturated with V2O5, resembles qualitatively that of polycrystalline V2O5 and MnO2. Attempts to fit applicable to MnO2 were only partially successful. (Author), Rept. on Electrochemistry of Primary Oxide Electrodes.

The equilibrium between F centers and M centers in additively colored KC1 was studied at temperatures between 60C and 130C. The M-center concentration at equilibrium varied approximately as the square of the F-center concentration, verifying the stoichiometric equation: 2F = M. At 60C, the equilibrium constant was 1.7 x 10 to the-19th power cu.cm. Enthalpy change = -4.1 Kcal and entropy change = -98 cal/deg, for the standard state one center cu.cm. The entropy change value agrees with that calculated from the configurational entropy, i.e., R 1n 6/N, where N is the concentration of negative ion sites. (Author)

The purpose of the work was to calculate the electronic energy levels of the simplest of these models, the unassociated alkaline earth cation with one trapped electron. The problem is treated as a one-electron problem, and the solution is estimated by using one-parameter hydrogen-like trial wave functions in a variational procedure. The impurity cation is treated as a substitutional distributed charge, the distribution being determined from the statistical procedure of Thomas and Fermi. The host lattice is considered to be an essentially continuous dielectric medium, the only discontinuity being the spherical cavity in which the divalent cation is placed. Account is taken of the lattice polarization by using an effective dielectric constant that is a function of both the high- and low-frequency dielectric constants. (See also AD-415 999). (Author), Report on A Magnetic Study of Color Centers in Alkali Halides.

A discussion is presented on the properties of Group IV substituents in Group III-V compounds. The electrical properties of GaSb with Sn as a substituent are calculated from thermodynamic considerations. The cases of a substituent as an acceptor or a donor, and of pair formation are considered. The general approach has been to calculate the free energy difference for substitution of a Group IV atom in a Group III and in a Group V site. (Author)

Single crystals of potassium chloride were grown from aqueous solution. X-ray darkenability and optical bleaching rate of F centers were measured at room temperature and the rate expressions were obtained experimentally for the processes. X-ray darkenability was also studied in crystals containing secondary centers, such as M, R, and N centers, which were produced by the preceding optical bleaching of F centers. Upon x-ray irradiation, F centers formed rapidly with the sudden decrease of the secondary centers. The same rate expression as that obtained for the F-center formation in virgin crystals is also applicable to this process. In this case the rate of F-center formation is dependent on the number of F centers bleached by the preceding optical bleaching but not on the kind of crystals. (Author)

Report on A Magnetic Study of Color Centers in Alkali Halides.

A study was made to determine if the mechanism of the discharge and recovery of the V2O5 electrode was analogous to that proposed by Coleman for the MnO2 electrode. The discharge and recovery of the V2O5 electrode, at moderate current densities and in solutions in the pH range from two to five, were found to resemble closely these processes in MnO2. The discharge consists of reduction of the V2O5 followed by the diffusion of the discharge product, presumably by the motion of protons and electrons, into the body of the solid. The recovery consists of the continued diffusion of the discharge product, without further reduction, which increases the activity of the vanadium pentoxide on the surface and hence increases the electrode potential. (Author), Report on Electrochemistry of Primary Oxide Electrodes.