DC conductivity in barium hexaferrites doped with bismuth oxide

Abstract

Barium hexaferrites of compositions BaO·(6-x)Fe₂O₃·xBi₂O₃ with 0 \leqslantx \leqslant0.4 have been synthesized by the ceramic calcination route. The bismuth substituted hexaferrites exhibit dc electrical conductivities more than two orders of magnitude higher than the pure ones. This is believed to arise due to an increase in the concentration of Fe²⁺ ions as a result of the presence of Bi⁵⁺ ions in these compounds. The dc conductivity at temperatures higher than 250 K can be explained on the basis of a non-adiabatic hopping model of small polarons, the variable valence iron ions forming the polaronic sites. At temperatures lower than 220 K a variable range hopping mechanism appears to control the conductivity.