Effect of ytterbium on the electrical properties of Li-Co ferrite

The real part: of the dielectric constant epsilon ' as well as the ac resis tivity of the rare earth ferrite Li0.5+ZYbxCozFe2.5-2z-xO4, 0.0 less than o r equal to x less than or equal to 0.2, z = 0.1 were measured at different temperatures (300-800K) as a function of frequency (10 kHz-5 MHz). More tha n one hump was obtained due to the presence of different polarization proce sses and conduction mechanisms. The obtained data were discussed on the bas is of the valence exchange between (Fe3+, Fe2+), (Fe2+, Yb3+) and (Fe3+, Co 2+). The values of the activation energy indicate the semiconducting proper ties of the investigated samples. Theoretical fitting was carried out for t he samples with different Yb concentrations and the reported data were foun d to be typical. The interaction mechanisms for the samples under investiga tion have been studied in the temperature range (300-800 K). (C) 2001 Elsev ier Science Ltd. AU rights reserved.