DIELECTRIC-RELAXATION OF PAIRED DEFECTS IN PEROVSKITE-TYPE OXIDES

A number of Debye-type dielectric relaxation peaks have been observed for acceptor-doped KTaO3 and CaTiO3, both of which have the perovskite structure. In the case of KTaO3,the dopants are divalent and trivalen t cations of the iron group, while CaTuO(3) is doped with Al3+. These peaks occur at relatively low temperatures and have activation energie s in the range 0.1-0.4 eV, much lower than the activation energy for t he conductivity. They are attributed to M-V-0 pairs, where M represent s the dopant ion and V-0 the oxygen ion vacancy. The possibility that the peaks are due to partial reorientation of the pairs in ''off-cente r'' configurations is ruled out by electron paramagnetic resonance wor k on Mn-doped KTaO3 by Geifman and coworkers (I.P. Bykov, I.N. Geifman , M.D. Glinchuk and B.K. Krulikovskii, Sov. Phys. Solid State, 22 (198 0) 1248). They must therefore be due to full reorientation, and possib le reasons for the low activation energy are discussed. A study of the peak heights shows that a large correction for internal field effects is necessary for KTaO3, but this correction is not nearly so large as that given by the Lorentz factor.