Order and Disorder in SrTiO 3 and in Pure and Doped KTaO 3

Radio-frequency dielectric dispersion is reported for SrTiO 3 and KTaO 3 :X, where X = Nb, Na, Li and zero. For all samples except KTaO 3 :Li, the dominant dispersion arises from Debye-type relaxation with one well-defined relaxation time of the order of 10 -8 s. These findings are identical with those in prototype ferroelectrics having an order-disorder type transition, e . g ., KH 2 PO 4 . Li-doping quenches Debye relaxation in favour of a polydispersive audiofrequency relaxation step. Li ions (and to a limited extent, Na ions) impose their random-site disordered dynamics on the polar configuration of KTaO 3 :X which is reached by a gradual freeze of uncorrelated polar motion.