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

The manifestation of dimensionalities and SiO2 shell induced modifications in structural, vibrational, dielectric and magnetic properties of microcrystalline, nanocrystalline BiFeO3 and core-shell structured BiFeO3@SiO2 nanoparticles are reported. Transmission electron microscopy image confirmed the core -shell structure of BiFeO3@SiO2 nanoparticles with BiFeO3 core similar to 50-90 nm and SiO2 shell similar to 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 SiO2 shell includes very small compressive stress of Bi-O and increases tensile stress of the Fe-O bonds in comparison with BiFeO3 nanoparticles. SiO2 shell on BiFeO3 nanoparticles reduces the dielectric constant and loss in comparison with microcrystalline and nanocrystalline BiFeO3 samples. The magnetic measurement indicated the existence of room-temperature weak ferromagnetism in BiFeO3 and core-shell BiFeO3@SiO2 nanoparticles, whereas bulk BiFeO3 showed antiferromagnetic nature (almost paramagnetic in nature), which is also endorsed by second order Raman modes. The influence of the grain boundary specific area (SGB) on ferromagnetism in microcrystalline and nanocrystalline BiFeO3 samples has been deciphered. (C) 2016 Elsevier B.V. All rights reserved.