Ravishankar Harani

A comparative study of the effects of rare-earth oxides on the physical, optical, electrical and structural properties of vanadium phosphate glasses

The physical parameters such as density, X-ray diffraction, infra-red absorption spectra and optical absorption measurements are discussed with respect to all compositions. The d.c. conductivity was measured for semi-conducting vanadium phosphate glasses containing 5 mol% rare-earth oxides. The conductivity of vanadium phosphate glasses is slightly higher than the corresponding compositions with rare-earth oxides. The heat treatment in the range 300 to 500° C caused progressive microstructural changes which dramatically affected the electronic conductivity (σ) and the activation energy for conduction (W). It was also found that the incorporation of rare-earth oxides did not affect the limits of the ultra-violet absorption edge of the base glass.

Electron spin resonance in phosphate glasses containing mixed transition metal ions

Phosphate glasses containing mixed Cu2+/Ni2+ and Cu2+/Co2+ oxides have been examined. A pronounced decrease in the optical absorption at 830 nm due to the Cu2+ ions is observed as the CuO in the glasses is gradually replaced by NiO or CoO and the decrease is accompanied by a pronounced decrease in the strength of the electron spin resonance (ESR) signal at 9.52 GHz. By combining the ESR and optical absorption data it is concluded that the decrease in concentration of Cu2+ ions in phosphate glasses may be due to an oxidation-reduction mechanism between two valency states of the two different transition metals, of the form Cu2++Ni+→Cu++Ni2+ and Cu2++Co+→Cu++Co2+.

Electrical conduction in copper phosphate glasses containing nickel or cobalt

A variation in d.c. conductivity and activation energy of 35 mol%CuO-65mol%P2O5 glasses is observed as CuO is gradually replaced by NiO or CoO. These results are believed to be due to the change in the redox ratio of the two transition metal oxide glasses, which causes an increase and then a decrease of polaron hopping transitions between the ions of the same element and between the ions of the different transition metal elements.

Electrical conductivity of praseodymium phosphate glasses

Mesures de conductivite en courant continu sur une serie de verres binaires Pr 6 O 11 −P 2 O 5 , entre 293 et 573°K