Experimental and first principles investigation of the multiferroics BiFeO₃ and Bi_0.9Ca_0.1FeO₃: Structure, electronic, optical and magnetic properties

We propose first-principles methods to study the structure, electronic, optical and magnetic properties of BiFeO₃ (BFO) and Bi_0.9Ca_0.1FeO₃ (BCFO). The morphology, optical band gap as well as magnetic hysteresis also have been investigated using experimental methods. X-ray diffraction data shows that Bi-site doping with Ca could result in a transition of crystal structure (from single phase rhombohedral (R3c) to two phase coexistence). Changing of Fermi level and decreasing of band gap indicating that the Ca-doped BFO exhibit a typical half-metallic nature. The optical absorption properties are related to the electronic structure and play the key role in determining their band gaps, also we have analyzed the inter-band contribution to the theory of optical properties such as absorption spectra, dielectric constant, energy-loss spectrum, absorption coefficient, optical reflectivity, and refractive index of BCFO. Enhancement of magnetic properties after doping is proved by both experimental and calculated result, which can be explained by size effect and structural distortion.