Electronic and ionic polarizabilities in some rutile type crystals

Abstract

In several earlier papers (1-J), we suggested that certain transition metal oxides with a high dielectric constant as well as large refractive indices such as TiO&-utile), W03, and H-Nb205 use crystallographic shear (CS) planes to accommodate nonstoichiometry. In view of the correlation between a high dielectric constant and CS planes, the relaxation due to polarizabilities seems to be one of the factors which predisposes such a material to this type of stoichiometric change. To reveal this correlation in greater depth, we have calculated electronic and ionic polarizabilities of i-utile, because the most reliable experimental data are available for this crystal compared to W03 and H-Nb205 . We found that rutile has an extremely large value for the electronic polarizability of the anion (2, 3); this polarizability appears to be one of the most important factors in formation of CS planes. To compare the electronic polarizability of the anion in TiOz with that of other r-utile-type crystals, we have determined polarizabilities of Ti02 ,i SnOz , Pb02 , MgF2 , and ZnFz , the dielectric properties of which have been obtained qperimentally.