Study of structural aspects of V2O5-P2O5-B2O3 glasses

V2O5-P2O5-B2O3 glasses have been prepared by the conventional melt-quench method and their transport characteristics and structural aspects have been investigated using different techniques. Replacement of P2O5 by B2O3 has been found to increase the room temperature conductivity and decrease the reduced metal ion ratio C defined as [V4+]/([V4+] + [V5+]). DC electrical conductivity measurements carried out at variable temperatures revealed that above 225 K, the conduction mechanism follows phonon-assisted small polaron hopping. Phosphorus and boron structural units have been characterized by P-31 and B-11 magic angle spinning nuclear magnetic resonance spectroscopy. V2O5-P2O5-B2O3 glasses contain both trigonal and tetrahedral boron configurations unlike pure V2O5-B2O3 glasses which contain boron only in trigonal configuration. P-31 MAS NMR studies clearly revealed that in these glasses, boron structural units are not interacting with phosphorus structural units. The change in the reduced vanadium metal ion ratio is found to follow the mole fraction of BO4 structural units. The change in coordination behavior of boron is attributed to the transfer of an electron from the electron-rich V4+ site to the electron-deficient BO3 units, thereby forming the tetrahedral boron structural units. (C) 1999 Elsevier Science B.V. All rights reserved.