Structural, optical and dielectric studies of Er substituted zinc ferrite nanospheres

The cationic distributions among tetrahedral and octahedral sites in spinel ferrites have a profound influence on their properties. Many studies were reported with various transition metal (TM) and rare earth (RE) cations distribution. We report the synthesis, structural, morphology, lattice vibrational, optical and dielectric properties of heavy RE cation (Er) substituted ZnFe2O4 as a function of different experimental parameters. The coprecipitated and calcined ZnFe2.xErxO4 (x = 0, 0.2, 0.4, 0.6 & 0.8) compounds crystallizes in cubic spinel structure and show narrow particle size distribution due to surfactant PEG. Particle size reduces (27-16 nm) with enhance of epsilon(r) concentration (x = 0 to 0.8) in the compounds. The EDAX spectra of the samples incorporation Er3+ ions into the lattice and the cubic lattice parameter enhances with Er3+ concentration. The lattice vibrational spectra reveal that the particles surface were free from surfactant PEG. Optical excitation studies show that energy band gap (Eg) of compounds reduces (1.85-2.00 eV) with enhance of Er concentration. The temperature, as well as frequency dependent dielectric constant (epsilon(r)') of ZnFe2-xErxO4, shows enhanced epsilon(r) with Er concentration up to x = 0.4 and then reduces with further enhancing of Er concentration. The dielectric loss factor (epsilon(r)) show similar variation with Er concentration. Further, both epsilon(r)' and epsilon(r) were reduced with enhancing of field frequency. In addition, both sr and er were enhanced with temperature and showed exponential change at low frequencies and high temperature and is attributed magnetic transition at around 525 K. The interface polarization mechanism is the predominant one in the present samples. The ac impedance spectra show two semicircles and each semicircle results from dielectric relaxation due to either particle (grain) or particles interface (grain boundary) polarization. The ac impedance reduces with enhancing of temperature. From the above studies, it is concluded that ZnFe1.6Er0.4O4 composition was best for high epsilon(r)' and epsilon(r) values at low frequencies. All samples could be used in high-frequency application.