Composition-dependent structural, physical, optical, and electrical properties of Ba0.5Ca0.5EuxFe12-xO19 hexaferrites for prospective applications

The Ba0.5Ca0.5EuxFe12-xO19 (x = 0, 0.5, 1.0, 1.5, and 2.0) series of samples with crystallite size 29-38 nm were prepared using the co-precipitation synthesis technique. The X-ray diffraction pattern analysis confirms the hexagonal structure of the Ba0.5Ca0.5EuxFe12-xO19 samples. The value of lattice parameters of the Ba0.5Ca0.5Fe12-xO19: xEu samples increased as compared to the pure Ba0.5Ca0.5Fe12O19 sample. This increase is related to cation substitution i.e., smaller cations (Fe3+ ions) are replaced by larger cations (Eu3+ ions). The crystallite size of the Ba0.5Ca0.5Fe12-xO19: xEu samples decreases continuously with increasing Eu3+ ions substitution. The shifting of octahedral and tetrahedral clusters was observed in the FTIR spectra due to substitution of Eu3+ ions. The photoluminescence (PL) spectra of the Ba0.5Ca0.5EuxFe12-xO19 samples were observed at 365 nm which corresponds to D-5(4) - F-7(0) transition of Eu3+ ions. The PL spectra shifted toward the higher wave length side for x = 1.0 due to reabsorption. The dielectric dispersion in the Ba0.5Ca0.5EuxFe12-xO19 samples can be understood by Maxwell-Wagner type of interfacial polarization based on Koop's theory. The increased hopping rate at octahedral sites due to the substitution of Eu3+ ions is responsible for a higher dielectric constant. The activation energy of the Ba0.5Ca0.5EuxFe12-xO19 samples was estimated from the temperature dependence of dc conductivity plots. The frequency dependency of ac conductivity of Ba0.5Ca0.5EuxFe12-xO19 samples can be described on the basis of Jonscher's power law and correlated barrier hopping (CBH) model. Below 380 K, the CBH mechanism describes the conduction mechanism, and above 380 K, the conduction mechanism can be understood by small polaron tunneling without overlapping (NSPT) model in the Ba0.5Ca0.5Fe12O19 compound. In the Eu-substituted Ba0.5Ca0.5Fe12O19 compound, only CBH mechanism dominates in the conduction process for all the temperatures. The Ba0.5Ca0.5EuxFe12-xO19 samples exhibit non-Debye dielectric behavior as confirmed by complex impedance spectroscopy analysis. By substituting Eu3+ ions, dielectric constant increases drastically and dielectric loss decreases as compared to pure sample. This indicates that the Ba0.5Ca0.5EuxFe12-xO19 samples can be potentially applied for microwave absorbers.