A comparative study on structural, vibrational, dielectric and magnetic properties of microcrystalline BiFeO3, nanocrystalline BiFeO3 and core–shell structured BiFeO3@SiO2 nanoparticles

The manifestation of dimensionalities and SiO 2 shell induced modifications in structural, vibrational, dielectric and magnetic properties of microcrystalline, nanocrystalline BiFeO 3 and core–shell structured BiFeO 3 @SiO 2 nanoparticles are reported. Transmission electron microscopy image confirmed the core–shell structure of BiFeO 3 @SiO 2 nanoparticles with BiFeO 3 core ∼50–90 nm and SiO 2 shell ∼16 nm. X-ray diffraction and Raman spectroscopy results show the presence of distorted rhombohedral structure with R3c space group in all samples. Bond valance sum (BVS) calculations shows the SiO 2 shell includes very small compressive stress of Bi–O and increases tensile stress of the Fe–O bonds in comparison with BiFeO 3 nanoparticles. SiO 2 shell on BiFeO 3 nanoparticles reduces the dielectric constant and loss in comparison with microcrystalline and nanocrystalline BiFeO 3 samples. The magnetic measurement indicated the existence of room-temperature weak ferromagnetism in BiFeO 3 and core–shell BiFeO 3 @SiO 2 nanoparticles, whereas bulk BiFeO 3 showed antiferromagnetic nature (almost paramagnetic in nature), which is also endorsed by second order Raman modes. The influence of the grain boundary specific area (S GB ) on ferromagnetism in microcrystalline and nanocrystalline BiFeO 3 samples has been deciphered.