Structural investigation of amorphous Na2O-P2O5-B2O3 correlated with its ionic conductivity

A series of sodium borophosphate compounds was prepared by twin roller quenching technique. The compounds have the following compositions: (10B(2)O(3)-(90 - x) P2O5 - xNa(2)O) (BPNax) and (10Na(2)O-(90 - x) P2O5 - xB(2)O(3)) (NPBox) with x = 0, 5, 10, 15, 20 mol%. DTA and XRD are used to evidence the crystallization conditions. Change in the local structural environment has been investigated by Raman and by B-11, P-31 MAS and QMAS NMR spectroscopies. The large P-31 chemical shift of P-3 and P-2 units with increasing x and the decrease in B-11 chemical shift of B-4 units with decreasing x indicate that phosphorous is linked to boron through a BO. This feature reveals that the short-range order is amended in the network. Optical absorption was used to determine glassy energy gap E-g, which we used to calculate size polydispersity index and optical index. Electric and dielectric properties were investigated through impedance spectroscopy. For all compositions, variation in the temperature of dc conductivity was found to follow an Arrhenius type relationship. An improvement in the ionic conductivity was reported with the increase of both alkali and borate contents in the glass host. (C) 2014 Published by Elsevier B.V.