Colossal dielectric response and relaxation properties caused by Mg doping in Co2Y-Type hexaferrites

摘要

Mg doping effects on the dielectric response and relaxation behavior in Ba2Co2-x MgxFe12O22 are experimentally studied for doping range of 0 <= x <= 1 through measurements of dielectric constant, loss and impedance spectroscopy as functions of temperature and frequency. It is shown that a colossal dielectric response with dielectric constant higher than 10(3) near room temperature for a wide range of frequency up to similar to 1 MHz can be realized by Mg doping at Co sites. Our results demonstrate that Mg doping can cause three obvious effects, namely, (i) to decrease Co3+ ions and in turn increase Fe ions in octahedrons, (ii) to raise the activation energy of relaxation and (iii) to increase resistance and capacitance of grain boundary. Our results also demonstrate that the dielectric relaxation is gradually changed from the intragranular- to the intergranular-dominated relaxation with increasing Mg doping content, perhaps due to the doping-caused increase in both resistance and capacitance of grain boundary.