Non-arrhenius stretched exponential dielectric relaxation in antiferromagnetic TiBO₃ single crystals

Dielectric spectra of TiBO₃ single crystals, grown by the chemical vapor transport technique, have been studied at temperatures between 40 and 200°C and frequencies from 100 Hz to 1 MHz. The shape of the spectra is well parameterized in terms of the temperature-independent Kohlrausch-Williams-Watts (stretched exponential) form, modified with the superimposed low-frequency dispersion and dc component. A deviation of the relaxation time from the Arrhenius law has been observed, which cannot be fitted into the known formulas. This deviation is phenomenologically explained by the screening effect. A formula has been proposed to describe such a complex dielectric relaxation behavior that is expected to exist in many more materials.