Identifying the nature of dielectric anomalies in SrFeO3-δ

Earlier comprehensive study of SrFeO3-delta series of compounds showed interplay between the oxygen vacancy and the magnetic and transport properties of the system. We have synthesized a powder sample of SrFeO3-delta series with oxygen vacancy in the range 0.15 <= delta <= 0.19. X-ray powder diffraction confirms the tetragonal crystal structure of the compound while the magnetic data indicates the presence of response from both orthorhombic (Sr4Fe4O11) and tetragonal (Sr8Fe8O23) phases which is common for the series with intermediate compositions. The temperature dependent dielectric measurements have been carried out in the 10 kHz-1 MHz frequency range. The dielectric constant and loss are found to be nearly temperature independent for Delta T similar to 170 K around room temperature. This temperature independent response could possibly be referred to as 'flat loss' corresponding to a low loss behavior, making the compound a potential candidate to capacitor industry. The anion stoichiometry has been further manipulated by introducing a more electronegative fluoride anion in the vacant oxygen sites where the structure changes to cubic one at room temperature.