Gadolinium-substitution induced effects on the structure and AC electrical properties of cobalt ferrite

We report on the frequency (f=20 Hz-1 MHz) and temperature (T=300-600 K) dependent electrical properties of gadolinium (Gd) substituted cobalt ferrite (CoF2−xGdxO4 (CFGO); x=0.00-0.40). Gd-substituted cobalt ferrites crystallize in cubic inverse spinel phase. CFGO materials exhibit lattice parameter expansion from 8.373 Å (x=0.0) to 8.422 Å (x=0.4) due to the larger ionic radius of Gd3+ compared to Fe3+. The effect of Gd-substitution is significant on the electrical properties; electrical conductivity decreases with increasing Gd-concentration. A two-layer model consisting of semiconducting-CFGO-grains separated by insulating grain-boundaries was able to account for the observed temperature and frequency dependent electrical properties.