Thermal and substituting effects of transition metal ions (Cr 3+ or Mn 4+) on physical properties of (V 2O 5) 0.8-(P 2O 5) 0.2 glass

Abstract

The effect of introducing transition metal ions of Cr 3+ and M 4+ annealing on the physical properties of (V 2O 5) 0.8-(P 2O 5) 0.2 glass was studied. Three glasses of (V 2O 5) 0.8-(P 2O 5) 0.2, (V 2O 5) 0.7-(P 2O 5) 0.2-(MnO 2) 0.1 and (V 2O 5) 0.7-(P 2O 5) 0.2-(Cr 2O 3) 0.1 have been prepared by melting in an open crucible. The thermal analysis (DTA and TG) of the glasses were recorded. The glass transition ( T g) and the crystallization temperature ( T c) were found to be composition dependent. The X-ray diffraction confirmed the amorphous nature for the virgin samples and the formation of some crystalline phases for annealed samples at 673 K for 24 h. The FTIR spectra of the virgin and annealed samples have been recorded and briefly discussed. The density and the molar volume of the glasses were found to be changed with the composition and the heat treatment of the glasses. The temperature dependence on the dc-electrical conductivity measurements for these glasses is studied over a temperature range from room temperature to 573 K. It was found that the dc-conductivity increases by annealing and decreases by substituting the vanadium by Cr 3+ or Mn 4+. This is explained on the basis of the change occurring in redox pairs ratio during the preparation and the heat treatment of the samples. Electrical conduction was interpreted on the basis of polaron hopping mechanism. The I– V characteristics were measured at room temperature. The I– V behavior shows three regions of conduction, namely, high resistance state (OFF state), turnover point with zero-differential resistance region (∂ V/∂ I = 0) and a differential negative resistance region. The turnover point is dependent on composition. The data in the range up to turnover point are discussed on the basis of an electrothermal process. All results are discussed and correlated on the basis of hopping mechanism between redox pairs.