Small Polaron Hopping And High-Temperature Dc Conductivity Of Chalcogenide Glasses

D.C. conductivity behaviour of a variety of chalcogenide glasses have been analysed using ln σ vs Image plots as suggested in the multiphonon assisted polaron hopping model of Triberis and Friedman. The agreement with the model is very satisfactory and further analysis of the model using c.

Oxygen desorption from high Tc YBa2Cu3O7−δ (δ = 0.05, 0.5)

From a temperature programmed desorption study employing a quadrupole mass spectrometer, the superconducting oxide YBa2Cu3O7−δ (δ = 0.05) showed two distinct oxygen desorption peaks, one below and one above 470°C. The activation energy of oxygen desorption of the superconducting oxide was 28 Kcals/mole and that of non-superconducting oxide (YBa2Cu3O6.5) was 54 Kcals/mole. No impurity peaks due to H2O, CO and CO2 from the bulk or adsorbed on surfaces could be observed when a well prepared superconducting oxide was heated up to 650°C.

Surface electronic structure of the high-Tc oxides

Electron energy loss spectroscopy (EELS) has been employed to monitor surface conductivity changes in YBa2Cu3O7 as a function of temperature. Concomitant use of x-ray photoelectron spectroscopy (XPS) establishes that the formation of oxygen dimers with lowering of temperature is accompanied by a simultaneous increase of surface conductivity.