A. Dias et Rl. Moreira, CONDUCTIVITY BEHAVIOR OF N-TYPE SEMICONDUCTING FERRITES FROM HYDROTHERMAL POWDERS, Journal of materials research, 13(8), 1998, pp. 2190-2194
The frequency and temperature dependencies of the dielectric permittiv
ity and of the electrical conductivity of excess ferrous ions hydrothe
rmal NiZn ferrites were analyzed before and after sintering. A decreas
ing tendency with frequency of the dielectric responses was observed,
but the high permittivities attained (epsilon' approximate to 10(5)) m
asked any relaxation in these materials. This behavior is characterist
ic of n-type semiconducting ferrites, where electron hopping between F
e+2 and Fe+3 ions leads to very high conductivity values. The temperat
ure dependence of the dielectric permittivities revealed the existence
of broader peaks. The electron hopping mechanism leads to a frequency
dispersion of the temperature where the permittivities attain their m
axima, The electrical conductivity variations with temperature exhibit
ed Arrhenius-type behaviors, with activation energies ranging from 0.3
4 eV (hydrothermal powder) to 0.16 eV (for the highest sintering tempe
rature). These results were correlated to the variations in Fe+2 conce
ntration and microstructure.