Influence of structural defects on the physical properties of BiFeO3

This work is the first to study the influence of crystallite sizes and structural defects on the crystal structure and physical properties of bismuth ferrite BiFeO3 (BFO). Rotatable Bridgman anvils were used to generate the structural defects, with the uniaxial pressures ranging from 0.5 to 1 GPa. According to the X-ray diffraction analysis (XRD), the symmetry space group R3c remains unchanged over the entire pressure range. From the results of the complex impedance spectroscopy, it was found that the relaxation has a non-Debye character and the activation energy increased from 1.48 eV to 2.48 eV for the starting and mechanically activated samples at 1 GPa, respectively. The crystal lattice dynamics were studied by optical and FTIR spectroscopies, and it has been found that Eg varied in the range of 2.18–2.33 eV, whereas the force constant showed variation in the range of 2.2–2.4 N/cm, depending on the applied mechanical activation pressure. The magnetization curves M(H) have been described by the law of approach magnetization to saturation (LAS). Also, a possible critical crystallite size of 70 nm has been determined, at which Hc and Mr reach their maximum values.