Colossal dielectric response and relaxation properties in Co2Z type hexaferrites
Abstract Polycrystalline samples of Sr 3 Co 2 Fe 24 O 41 and Ba 3 Co 2 Fe 24 O 41 have been prepared by a sol gel method. The XRD data indicate that the samples are Co 2 Z type hexaferrites with the centrosymmetric space group of P6 3 /mmc The SEM micrographs suggest that mixture plate like grains are formed and Sr 3 Co 2 Fe 24 O 41 shows more dense grain structure. High temperature dielectric relaxation behaviors are studied in a wide range of frequency and temperature through dielectric and impedance spectroscopies analysis. Colossal dielectric permittivity is observed at low frequency and dielectric relaxation behavior is clearly seen at high temperatures. Two types of relaxations are observed in Sr 3 Co 2 Fe 24 O 41 and it is attributed to the thermally activated model which follows the Arrhenius law. The X ray photoelectron spectroscopy indicates that Fe 2+ and Fe 3+ coexist in the system and the dielectric relaxations originate from the carriers hopping between Fe 2+ and Fe 3+ Moreover, the high concentration of Fe 2+ in Ba 3 Co 2 Fe 24 O 41 causes the high dielectric permittivity at low frequency range and the relatively low conductivity at high temperature.