Comparative studies by X-ray diffraction, Raman, vibrating sample magnetometer and Mössbauer spectroscopy of pure, Sr doped and Sr, Co co-doped BiFeO3 ceramic synthesized via tartaric acid-assisted technique

Pure BiFeO3 (BFO), Sr-doped Bi0.97Sr0.03FeO3 (BSFO) and Sr, Co co-doped Bi0.97Sr0.03Fe0.8Co0.2O3 (BSFCO) samples have been prepared via a tartaric acid-assisted sol-gel technique. Investigation of the structure, lattice dynamics, magnetization and hyperfine interaction have been performed through X–ray diffraction (XRD), transmission electron microscope (TEM), Raman spectroscopy (RS), vibrating sample magnetometer (VSM) and Mössbauer spectroscopy (MS). The TEM images show that the particle sizes of BFO, BSFO and BSFCO are respectively 11.4, 12.1 and 8.8 nm. The XRD analysis reflects a structural phase transition from rhombohedral R3c structure in case of BFO and BSFO samples to two phase coexistence (rhombohedral R3c and trigonal R–3m:R) in case of BSFCO sample. This structural phase transition has been strongly confirmed by the alterations in the vibration modes observed in Raman spectra (expansion, shift, merge, and reduced intensity). Second order vibration modes, corresponding to the two-phonon scattering in the range 650–1000 cm−1, have been recorded for all samples. Investigation of magnetic properties reveals that pure and Sr doped samples possess considerably high magnetic saturations (Ms = 5.61 and 5.79 emu/g respectively). Additionally, BSFCO sample shows enhancement in Ms (Ms rises to 8.26 emu/g). Suppression of spiral spin structure caused by the small nano-size has been assumed. The destruction of the spiral spin has been also suggested through M össbauer studies. The hyperfine parameters reveal that only Fe3+ is observed in two different nonequivalent trigonal distorted octahedral environments. The outcome of this work suggests the potentiality of Sr, Co co-doping to improve the structure and ferromagnetism of BiFeO3 ceramic making it feasible to be employed in enormous applications.