Synthesis of Bi₄Ti₃O₁₂ compounds via citrate method

Full text: Ferroelectric-piezoelectric ceramics generate intense force with a rapid response at high frequencies. Most piezoelectric materials used by industry are lead-based, such as perovskites Pb(Zr, Ti)O₃ (PZT), where lead is a highly toxic element and its use is regulated globally. Piezoelectric ceramics based on niobates and leadfree titanates are some examples of lead-free piezoelectric in their composition. Bi₄Ti₃O₁₂ has been largely studied recently due to its good electromechanical properties, being able to compete with PZT ceramics, especially for high temperatures applications. The synthesis of high quality Bi₄Ti₃O₁₂ ceramics is, however, challenging due to Bi volatilization, leading to the formation of secondary phases and non-stoichiometric compounds, lowering its piezoelectric properties. Here, ceramic powders are synthesized using a chemical route known as Citrate Method. Characterization studies were made by Simultaneous Thermal Analysis, X-Ray Diffraction, Scanning Electron Microscopy and Energy-Dispersive X-Ray Spectroscopy, in order to check the composition, morphology and phases in the samples. The calcination process was carried in the air at 500, 600, 700 and 800 °C, producing nanometric ceramic powders (~100 nm) with a single phase and high purity. At lower calcination temperatures the metastable Bi²Ti₂O₇ phase is present at a low mass fraction (< 5%). However, this was eliminated when heat treated at temperatures higher than 700 °C. Rietveld refinement shows that the increase in the calcination temperature leads to a cell volume closer to theoretical values, indicating a relaxation the crystal structure due to defects elimination. EDS analysis shows a Bi/Ti ratio of 1.44, a close value to the calculated (1.33). The observed Bi/Ti ratio did not change with an increase of the calcination temperature, indicating the suppression of Bi volatilization. The synthesis here presented has shown impressive results, is an excellent option for the production of high quality Bi₄Ti₃O₁₂ powders. 1219. (author)