The effects of defect system ordering in a weakly doped incipient ferroelectric (KTaO3): dielectric manifestation

The temperature-frequency behaviour of the permittivity ε '(T, f) and tan(δ (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% Cr; 3 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(δ (T)) maxima positions obeying the universal Arrhenius law with activation energy Δ = 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. (author)