The effect of local ordering in a system of defects in weakly doped KTaO3: Dielectric anomalies and their origin

The temperature-frequency behaviour of the permittivity ε′(T,f) and tgδ(T,f) (20-300 K, 120 Hz-9 MHz), EPR, optical absorption and luminescence of KTaO 3 single crystals, pure and with Li 0.1; Cr 0.02; Cu 3; Fe 1; Li 0.1 + Cr 0.1, and Li 0.1 + Cr 0.1 + Cu 0.02 wt.%, were studied. Below 70 K, in all the doped samples, dielectric dispersion occurs, with tgδ(T) maxima obeying Arrhenius law. This is associated with a local ordering in dipole-dipole clusters (which contain reorienting defects of various kind) with correlations due to interactions via the TO-soft mode.