Grain and grain boundary effects on the frequency and temperature dependent dielectric properties of cobalt ferrite–hafnium composites

We report on the frequency (f=20 Hz–1 MHz) and temperature (T=300–973 K) dependent dielectric properties of hafnium (Hf) incorporated cobalt ferrite (CoF2−xHfxO4 (CFO–Hf); x=0.00–0.20). The dielectric constant (εʹ) of CFO–Hf is T-independent at T<450 K, at which point increasing trend prevails. A grain bulk-boundary based two-layer model, where semiconducting-grains separated by insulating-grain boundaries, satisfactorily accounts for ε–T (>450 K) variation. Correspondingly, electrical responses in impedance formalism are attributed to the grain and grain-boundary effects which also accounts for the observed two dielectric-relaxations. The results demonstrate that the dielectric phenomena in CFO–Hf can be tailored by tuning Hf-concentration.