Assessment of hydrothermal parameters in the wet synthesis of α- and β-BiTaO4 by in situ synchrotron X-ray diffraction

Synchrotron X-ray diffraction was used for in situ monitoring of hydrothermal precursors calcination to obtain BiTaO4 in the orthorhombic (alpha) and triclinic (beta) crystal phases. Different precursors were prepared varying time (24 and 48 h) and temperature (150 and 200 degrees C) of hydrothermal treatment. According to the results of in situ X-ray analysis during calcination of the precursors, the alpha-and beta-BiTaO4 phases were achieved from the hydro thermal precursors treated at 200 degrees C. When the hydrothermal treatment time was carried out for 24 h, a precursor with Bi1-xTaxO1.5-x (fluorite structure, like delta-Bi2O3) and BiOCl phases was obtained, which evolved to Bi24Cl10O31 phase with heating. The presence of the chlorine-containing phases and the low crystallinity of the hydrothermal precursor contributed to the formation of beta-BiTaO4. When the precursor is obtained with 48 h of hydrothermal treatment, only the Bi1-xTaxO1.5-x crystalline phase was identified and when heated it evolved to alpha-BiTaO4 phase at 550 degrees C. This is the first time that the pure orthorhombic phase is obtained from a wet synthesis method. All identified phases were confirmed by Rietveld refinement.

Automated summary

In this study, synchrotron X-ray diffraction was used to monitor the calcination of hydrothermal precursors in situ, resulting in the synthesis of both orthorhombic and triclinic phases of BiTaO4. By varying the time and temperature of hydrothermal treatment, different precursor phases were obtained. The results showed that α-BiTaO4 and β-BiTaO4 phases were achieved when the precursors were treated at 200 degrees Celsius.