Role of Sr doping on transport and magnetic properties of bismuth ferrite in correlation with defect formation

Abstract

Doped Bi1−xSrxFeO3 samples were synthesized by solid state reaction method. Doping with alkaline earth metal (Sr) was used to suppress formation of second phase in order to improve electrical and magnetic properties. Investigations were carried out on samples of x = 0.2–0.4 where mainly single phase of cubic perovskite is formed without considerable traces of second phase from x = 0.3–0.4 as verified by X-ray diffraction using synchrotron radiation. The real part of the dielectric constant ( $${\varepsilon ^/}$$ ), dielectric loss (tan δ) and conductivity (σ) were measured at different temperatures as a function of the frequency (100–4000 kHz). Also, magnetic parameters were investigated at room temperature using Vibrating sample Magnetometer. Doping by Sr2+ gives rise to the formation of oxygen vacancies and conversion of Fe3+ into Fe4+. These defects were considered in the discussion of the results using structure-properties correlation. Electronic and ionic conductivity contribute to the measured conductivity. The ratio of free electrons to oxygen vacancies decreases with doping and this define predominant type of conductivity. The highest values of conductivity are observed in the range of pure single phase and the maximum value is achieved for the doping level of x = 0.35–0.4, i.e., material of high concentration of oxygen vacancies as well as absence of any traces of second phase. The frequency is more effective at low temperatures and in the range of doping level that results in maximum ratio of ionic/electronic conductivity. From the derived magnetic parameters, it is shown that BFO exhibits improved magnetization by Sr doping.