Electrical conductivity of β-ferrites with AI₂O₃ and Ga₂O₃

The present paper describes the synthesis and electrical conductivity of Al- and Ga-substitutedβ""-ferrites. AI- and Ga-substitutions for β""-ferrite (K₂9.75(Fe_1-x Me_x)₂O₃) are possible in the range x < 0.2 and x a≤0.4, respectively. There is an isotropic decrease of the lattice constants of -1.00% for an Al-substitution of x = 0.2, while there is an anisotropic decrease of -0.75% for a Ga-substitution. The bulk ionic conductivity of Al-substituted β""-ferrite is 3.0 × 10° S·1 (250 °C) at x = 0.2, which is slightly smaller than the value of the sample without substitutions. The grain boundary conductivity of Al-substituted β''''-ferrite, however, increases up to 6.1 × 10^-4 Snr' (250 °C) at x = 0.2, which is about 17 times higher than the value for β""-ferrite without substitutions. The bulk ionic conductivities of Ga-substitutedβ''''-ferrites are almost the same as those of the Al-substituted β''''-ferrites.