Highly enhanced dielectric permittivity in CoFe2O4 by the Gd substitution in the octahedral sites

Polycrystalline CoFe2-xGdxO4 (x = 0.0, 0.02, 0.04, 0.06, 0.08 and 0.1) were prepared by modified combustion technique intending to tune the dielectric properties of CoFe2O4 by the Gd substitution of Fe atoms in the octahedral sites. Enhancement of dielectric permittivity is observed with the increasing concentration of Gd in CoFe2O4. At higher levels of Gd substitution, CoFe2O4 shows ten times more dielectric permittivity than the pristine one. This enhancement of dielectric permittivity is mainly due to the increase of exchange interaction between Fe2+ and Fe3+ ions through induced strain, excess availability of Fe2+ ions in the lattice and grain - grain boundary contribution. Incorporation of larger ions in Fe sites induces a strain in the lattice due to the lattice mismatch in system. W-H plot is employed to study this induced strain in detail. Reitveld refinement technique explains the excess increase of Fe2+ ions. The excess increase of Fe2+ in CoFe2-xGdxO4 is further confirmed by XPS analysis. The role of grain-grain boundary influence on the dielectric permittivity is evident from Nyquist plots. Temperature and frequency-dependent dielectric spectroscopic studies were conducted in detail. All these results point to the fact that substitution with Gd ions in Fe sites tailors the dielectric properties of CoFe2O4, which helps to develop more advanced technologies in future. (C) 2020 Elsevier B.V. All rights reserved.