Enhanced magnetic and dielectric properties in bismuth ferrite (Bi_2−xSr_xFe₄O₉) derived by the reverse chemical co-precipitation method

Bi_2−xSr_xFe₄O₉, 0 ≤ x ≤ 0.25 (BSFO) powders have been successfully synthesized by the reverse chemical co-precipitation method with a pH value of 9 at room temperature. In this study, the effect of Sr²⁺ doping on the structural, morphological, magnetic and electrical properties of BSFO was investigated and then the as-prepared powders were fabricated by microwave sintering at 800 °C. The X-ray diffraction (XRD) reveals the formation of the pure phase orthorhombic structure with Bi₂O₃ impurity for samples with x = 0.15, 0.20 and 0.25. Also, XRD patterns showed that by increasing the Sr²⁺ concentration, the amount of Bi₂O₃ impurity increases. In addition, the field emission scanning electron microscopy (FESEM) indicates by increasing the Sr content, the particle size decreases from 215 for a pure sample to 40 nm for BSFO with x = 0.25, approximately. The thermogravimetric–differential scanning calorimeter (TG–DSC) and Fourier transform infrared spectroscopy (FT-IR) were carried out for the estimation and conformation of the as-selected calcination temperature, weight loss and vibrational bounding mode, respectively. The magnetic properties of the nanoparticles and dielectric properties of the bulk samples were measured using the vibrating sample magnetometer (VSM) and inductance–capacitance–resistance (LCR-meter), respectively. The magnetization (M) was elevated from 0.190 to 0.358 emu/g by adding the 0.10 and then falls down to 0.217 emu/g for x = 0.20 strontium molar ratio as a result of the spiral spin structure collapse and formation of diamagnetic Bi₂O₃ phase, respectively. Besides, a decrease in the particles size by increasing the Sr amount resulted in more uncompensated spins, thereby improving the saturation magnetization. Furthermore, The coercivity of as-synthesized powder samples greatly increase with increasing the dopant concentration from 125 Oe for pure BFO to 3289 Oe for samples with x = 0.10 and then decreases to 940 Oe for x = 0.25 due to increasing the non-uniformity in the grain size distribution by addition the more dopant ions. In addition, the dielectric constant and dielectric loss were improved up to x = 0.25.