Optical Basicity Of Fluorides And Mixed Oxide-Fluoride Glasses And Melts

An optical basicity study is made of crystalline fluorides and oxide-fluoride glasses using (i) data from probe ion spectroscopy, (ii) calculations based on chemical constitution, and (iii) the relationship of optical basicity, A, with electronic polarisability. The more recent developments in optical basicity are included so that up-to-date A values for binary oxides are used and also the highly significant effect of coordination number on optical basicity is taken in to account. Results indicate that the optical basicities of binary fluorides are one half those of the corresponding oxides, for example, ^(CaF2)=0.50 compared with ^)CaO)=1.00. It is shown that the optical basicities of complex fluorides such as Na [BF4] can be calculated by the same optical basicity methods as used for oxidic systems. Also, the relationship between fluoride polarisability and ^(fluoride) is found to be linear but different from the corresponding relationship for oxides. The problematic calculation of ^ for mixed oxide-fluoride systems is discussed.