Physical, electrical and dielectric properties of Ca-substituted strontium hexaferrite (SrFe12O19) nanoparticles synthesized by co-precipitation method

Calcium substituted strontium hexaferrite CaxSr1-xFe12O19 (x=0.0-0.6) nanoparticles are synthesized by chemical co-precipitation method. The synthesized samples are characterized by Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy, Transmission Electron Microscopy, DC electrical resistivity and dielectric measurements. FTIR data of uncalcined sample shows that nitrate ions are present which disappeared on calcination at 920 deg. C. The XRD data shows that a single hexagonal magnetoplumbite phase is formed in samples in which the calcium content, x, is ≤0.20. However, a nonmagnetic phase (α-Fe2O3) in addition to the hexagonal phase is also present in samples with x>0.20. The average crystallite size is found between 17 and 29 nm. The DC electrical resistivity increases with increase of calcium content up to level of x=0.2 but decreased on further addition of calcium. The enhanced resistivity of the calcium doped material has potential applications in microwave devices. The variations of dielectric constant and dielectric loss angle are explained on the basis of Maxwell-Wagner and Koops models.