ELECTRICAL AND STRUCTURAL STUDIES OF LITHIUM FLUOROPHOSPHATE GLASSES

Two different series of glasses, xF(2): (1-x)LiPO3 and xLiF: (1-x) LiP O3, have been synthesized by fluorination of LiPO3 and incorporation o f LIF in LiPO3, respectively. The effect of incorporation of fluorine by these two different methods in the short-range structure of phospha te glasses has been characterized using X-ray photoelectron spectrosco py (XPS), infrared and electrical studies. These results provide evide nce for fluorine participation in the phosphate network. Infrared resu lts indicate the presence of P(O, F)(4) and P-2(O, F)(7) species. XPS results show that O 1s spectrum could be deconvoluted into two peaks c orresponding to the non-bridging oxygens (NBO) and bridging oxygens (B O). Similarly, the F 1s spectrum consists of two peaks, showing clearl y the existence of two states of fluorine environments; the ratio of t hese two states varies with the fluorine content. These observations s uggest that fluorine atoms interact with both cations and anions leadi ng to both Li-F and P-F bonds. The number of U-F bonds increases with increasing fluorine content or LiF mole fraction. The de conductivity increases linearly, and the activation energy decreases with the incre ase of LiF content. The de conductivity and activation energy of fluor inated lithium phosphate glasses do not change as the fluorine concent ration increases. The conduction properties are discussed in terms of structural modification of LiPO, by fluorination/incorporation of LiF. The results suggest that LiF acts both as a dopant and as a network m odifier. The former is responsible for the increase of conductivity.