Dielectric and Structural Properties of Bi₅Ti₃FeO₁₅ Ceramics Obtained by Solid-State Reaction Process from Mechanically Activated Precursors

Abstract

Bi₅Ti₃FeO₁₅ (BTFO), an Aurivillius compound, was synthesized via sintering the Bi₂O₃ and Fe₂O₃ mixture and TiO₂ oxides. The precursor material was ground in a high-energy attritorial mill for (1, 3, 5, and 10) h. The orthorhombic system Bi₅Ti₃FeO₁₅ ceramics was obtained by a solid-state reaction process at 1313 K. Phase formation behavior was investigated using differential thermal analysis (DTA), thermal gravimetric (TG), and X-ray diffraction (XRD) techniques. The frequency-dependent properties of the material were investigated by impedance spectroscopy. The impedance spectroscopic method is widely used to characterize electrical properties of materials and their interfaces with electronically conducting electrodes. These studies indicate that 1h, 3h, and 5h primary high-energy ball milling followed by sintering is a promising technique for pure Bi₅Ti₃FeO₁₅ ceramic preparation, whereas the ceramics obtained from the substrates after 10h milling is a two-phase material. As the result of this investigation, the model of adjusting the Nyquist charts with a three-element R-CPE (constant phase element) series connection was proposed. It was found that the value of the dielectric constant at the Curie temperature decreases when the milling time of the substrates increases. The decrease in the dielectric constant is influenced by the great dispersion of the grains, their dense packing, and location of particular grains in relation to other grains. Moreover, the change of resistivity with frequency indicates that relaxation processes take place in the material. In conclusion, it was reported that the optimal milling time of precursor oxide powders for carrying out the sintering process is equal to 5 h. Then the obtained ceramics contain one phase and exhibit the highest dielectric properties for practical applications.