A. S. W. Li

Effect of annealing on the electrical and optical properties of V2O5-GeO2 glasses

Increases in the electrical conductivities of vanadium germanate glasses on annealing have been reported recently in the literature. The increases were attributed to the formation of microstructure on annealing. In the present work we report a study of the V2O5-GeO2 glass system using electron paramagnetic resonance, optical absorption, differential scanning calorimetry and electron diffraction techniques. The V2O5-GeO2 glass system consists of an equimolar mixture of vanadium pentoxide and germanium dioxide. One sample was unannealed and the other was annealed at 300° C for about 24 h.The results revealed that the increase in the electrical conductivity of the annealed samples could be attributed to the increase of reduced valence states of vanadium ions which accompany the microstructure formation and not solely to the structural change.

Absorption spectrum of trapped electrons in rhamnose single crystals x irradiated at 4 K

The stable optical absorption of x‐ray produced trapped electrons at 4.2 K in rhamnose single crystals has been observed under similar conditions to those in which the electrons have been identified by electron spin resonance. The absorption maximum is at 400 nm which compares with a transient absorption at 500 nm observed at 273 K by pulse radiolysis. The origin of the temperature shift and the electron trapping site are briefly discussed. (AIP)

Comparison of silver atom solvation in glassy and polycrystalline ices

Electron spin echo studies have been carried out for Ag0 in a 9 M sodium perchlorate aqueous glassy matrix at 4.2 K. The analysis of the nuclear modulation patterns shows that the hydration structure of Ag0 initially formed at 4.2 K is the same as that in polycrystalline ice. In contrast to polycrystalline ice, no change in the solvation structure takes place upon warming the sample to 77 K. The solvation process via OH bond rotation in polycrystalline ice is suggested to occur via defects in the ice structure adjacent to Ag0 in addition to hydrogen bonding interactions. (AIP)

Electron spin resonance of the solvation of radiation-produced silver atoms in alcohol-water mixtures: Comparative studies of preferential solvation in methanol, ethanol and n-propanol aqueous mixtures

Abstract Frozen solutions of silver salts exposed to 60 Co γ-irradiation form silver atoms by reaction of radiation-produced electrons with the silver ion. At 4K the silver atoms are initially produced in a nonequilibrium or presolvated state and upon brief thermal excitation to 77K the first solvation shell geometry changes towards an equilibrium or solvated silver atom. This is most pronounced in water but also occurs in methanol, ethanol and n -propanol matrices. The changes in the electron spin resonance magnetic parameters upon silver atom solvation have been determined. In alcohol-water mixtures Ag 0 is preferentially solvated by polycrystalline water at low alcohol concentration. Above a particular alcohol mole percent Ag 0 suddenly changes its environment to a glassy alcohol one. This sudden change occurs at 17, 13 and 6 mol % methanol, ethanol and n -propanol, respectively. These mole percents correlate with the minimum of the excess enthalpy of mixing and with the hydrogen atom trapping ability of these alcohol-water mixtures. The results also suggest that the local environmental disorder around Ag 0 increases with alcohol chain length in alcohol-water frozen solutions.

Kinetic study of the conversion of presolvated to solvated silver atoms in polycrystalline ice: Activation energy of water molecule rotation with D‐defect annihilation

The kinetics of the conversion of presolvated silver atoms formed in polycrystalline ice at 4 K to the solvated state has been studied in the temperature range of 38 to 49 K. The kinetics are approximately first order and give an activation energy of 0.09±0.01 eV. This is lower than the 0.24 eV activation energy for diffusion of orientational defects by water molecule rotation in ice and is identified with water molecule rotation together with D‐defect annihilation in the silver atom solvation shell. (AIP)