Dielectric properties due to crystallographic shear planes in chromia-doped rutile (TiO2)

Dielectric properties of rutile (TiO 2 ) doped with chromia (Cr 2 O 3 ) have been measured as a function of frequency between 30 Hz and 60 kHz at temperatures between 77 and 350 K. Two types of specimen were produced. One sort was prepared by heating (001) sections of rutile in Cr 2 O 3 pellets at 1173-1137 K for various times and then annealing them in air at 1373 K for 1 week ('oxidized' specimens). The other sort was prepared simply by just heating (001) sections in Cr 2 O 3 pellets ('as-doped' specimens). The dielectric properties depend on the frequency of measurement. The static dielectric constant of 'oxidized' specimens, which was measured at 293 K, increases with sample preparation time, while that of as-doped specimens increases when the heating time is short, but it decreases and increases again at prolonged heating times. In every specimen, a relaxation peak is distinguished by an activation energy of 0-2 eV in the temperature dependence of the dielectric loss tangent or loss factor. This relaxation has been discussed in terms of the formation of {132} crystallographic shear planes observed in electron microscope examinations. In addition, another relaxation peak with an activation energy of 0-5 eV is found in as-doped specimens heated for long periods, for example over 3 days at 1373 K. With increasing heating time the former relaxation peak decays, while the latter grows, which suggests that a transition from {132} crystallographic shear structures to another defect structure takes place as the content of chromium increases.