THE EFFECTS OF DEFECT SYSTEM ORDERING IN A WEAKLY DOPED INCIPIENT FERROELECTRIC (KTAO3) - DIELECTRIC MANIFESTATION

The temperature-frequency behaviour of the permittivity epsilon'(T,f) and tan[delta(T,f)] (20-300 K; 120 Hz-9 MHz), EPR, optical absorption and luminescence of KTaO3, nominally pure and weakly doped (0.1 wt% Li; 0.01 wt% Cu; 1 wt% Fe; 0.1 wt% Li + 0.1 wt% Cr and 0.1 wt% Li+0.1 wt% Cr+0.02 wt% Cu) were studied. Below 70 K, in all doped samples, dielectric dispersion occurs, with tan[delta(T)] maxima positions obeying the universal Arrhenius law with activation energy DELTA = 1000 +/- 50 K. This is associated with local ordering in the dipole-dipole clusters containing reorienting defect pairs of various kinds, with correlations due to interaction via the TO soft mode.