Novel TiO2-doped semiconducting hexagonal ferrites

Hexagonal ferrites are well known, globally important magnetic ceramics, with many applications in electronics and telecommunications, especially at microwave frequencies. However, for useful dielectric properties, it is usually required that they have a low degree of conductivity. This becomes an issue, as the high temperatures required for their processing (>1000 ºC) leads to the formation of small quantities of Fe2+ ions, which cause conductivity to increase. In this work, we decided to exploit this phenomenon, and actively try to encourage such conduction in a hexagonal ferrite, to the extent of making it a semiconductor. Barium hexaferrite (BaM, BaFe12O19) and strontium hexaferrite (SrM, SrFe12O19) were doped with 1 wt% and 5 wt% TiO2, and fired at 1000 ºC. The ?AC conductivity and dielectric properties ( real part of permittivity and dielectric losses) were investigated as function of frequency in a range of 100 Hz-1 MHz using Impedance Spectroscopy Technique. The BaM composites show high dielectric permittivity of about 150 for frequency higher than 104 Hz and high dielectric losses (higher than 100 %) for entire investigated range. A high dispersion of ?AC with frequency were obtained for all investigated composition. The resulting ferrites maintain their magnetic properties, but become semiconductive with conductivities up to 0.1 Ohm-1 m-1.