Structural, optical and dielectric properties of aluminum-substituted SrAl2xFe12-2xO19x = (0.0,0.2,0.4,0.6,0.8,1.0) M-type hexagonal ferrites

Aluminum-substituted M-type hexaferrites with nominal composition SrAl 2x Fe 12-2 x O 19 with x = (0.0,0.2,0.4,0.6,0.8,1.0) were successfully prepared by sol gel auto combustion route. The confirmation of M-type hexagonal ferrites with high purity phase was done by the XRD analysis. Lattice parameters a and c , c / a ratio and cell volume have been calculated. Lattice parameter ‘ a ’ varies from (5.86–5.88) Å, ‘ c ’ varies from (22.87 to 23.08) Å, Cell volume lies in the range of (687.10–688.90) Å 3 and crystallite size varies from 39 to 61 nm. Optical properties of materials were determined by optical bandgap. The value of bandgap E g was decreased linearly with the increase of Aluminum substitution and it approaches to maximum within energy range of 1.74 to 2.80 eV. Permittivity, permit loss, tan loss, ac conductivity, real and imaginary parts of electric modulus was also discussed. Maximum value of dielectric constant (15.5) was obtained for SrAl 2 x Fe 12-2 x O 19 at x = 1.0 composition at 2.5 GHz frequency. Similarly Maximum Q -value was obtained for this composition. On the basis of space charge polarization and hopping of electrons between Fe 3+ and Fe 2+ , the observed change in dielectric parameters have been explained. The Maxwell Wagner and Koop's models have been used to explain the change in ac conductivity as a function of frequency. Based on these properties, the prepared materials are highly recommended in high frequency devices such as modulator, sensing, switching, security and energy storage devices.