Structural and dielectric properties of molybdenum doped cobalt ferrite

Cobalt ferrite (CoFe2O4; referred to CFO hereafter) is one of the most promising materials from the ‘ferrites family’ with a large cubic magnetocrystalline anisotropy (1.8 – 3×10 5 Jm-3 at 300 K). CFO exhibits unique, distinct characteristics such as higher Curie temperature (~793 K), moderate saturation magnetization (80 emu/g), higher coercivity (5400 Oe), excellent chemical-structural stability, large Kerr effect, Faraday rotation and good mechanical hardness at room temperature. While it is well known that CFO is found in inverse spinel structure of the form AB2O4 , where O atoms are arranged in a face centered cubic lattice, A tetrahedral sites (Fe3+), and B octahedral sites (Co2+), it is also known that there are many unoccupied interstitial sites in the structure, which favors the movement of cations. To enhance dielectric properties for sensor applications, CFO needs to be doped with suitable metal ions. In this work, molybdenum (Mo) doped CFO (CoFe2-xMoxO4; referred to CFMO hereafter) ceramics were prepared using solid state reaction method with variable compositions (x= 0.0 - 0.3). Crystal structure, surface morphology and dielectric constant of CFMO were studied. X-ray diffraction (XRD) observations confirm that CFMO has inverse spinel crystal structure with a lattice expansion of ~8.3 Å with increasing Mo content and also increase in density of the compound. Scanning electron microscopy (SEM) analyses indicate an increase in grain size with increasing Mo content. The dielectric measurement results of pure CFO compared to those of CFMO compounds are enhanced because of the distortion created by the Mo incorporation attributed to the Maxwell-Wagner type polarization. The results demonstrate that the crystal structure, microstructure, and dielectric properties can be tuned by Mo incorporation in the CFMO ceramics