Electrical and structural studies of lithium fluorophosphate glasses

Abstract

Two different series of glasses, xF2: (1 - x) LiPO3 and xLiF: (1 - x)LiPO3, have been synthesized by fluorination of LiPO3 and incorporation of LiF in LiPO3 respectively. The effect of incorporation of fluorine by these two different methods in the short-range structure of phosphate glasses has been characterized using X-ray photoelectron spectroscopy (XPS), infrared and electrical studies. These results provide evidence for fluorine participation in the phosphate network. Infrared results indicate the presence of P(O, F)4 and P2(O, F)7 species. XPS results show that O 1s spectrum could be deconvoluted into two peaks corresponding to the non-bridging oxygens (NBO) and bridging oxygens (BO). Similarly, the F 1s spectrum consists of two peaks, showing clearly the existence of two states of fluorine environments; the ratio of these two states varies with the fluorine content. These observations suggest that fluorine atoms interact with both cations and anions leading to both LiF and PF bonds. The number of LiF bonds increases with increasing fluorine content or LiF mole fraction. The dc conductivity increases linearly, and the activation energy decreases with the increase of LiF content. The dc conductivity and activation energy of fluorinated lithium phosphate glasses do not change as the fluorine concentration increases. The conduction properties are discussed in terms of structural modification of LiPO3 by fluorination/incorporation of LiF. The results suggest that LiF acts both as a dopant and as a network modifier. The former is responsible for the increase of conductivity. © 1995.