Time-resolved in situ powder X-ray diffraction reveals the mechanisms of molten salt synthesis

We report the first use of high-energy monochromatic in situ X-ray powder diffraction to gain unprecedented insights into the chemical processes occurring during high temperature, lab-scale metal oxide syntheses. During the flux synthesis of the n = 4 Aurivillius phase, Bi₅Ti₃Fe_0.5Cr_0.5O₁₅ at 950 °C in molten Na₂SO₄ we observe the progression of numerous metastable phases. Using sequential multiphase Rietveld refinement of the time-dependent in situ XRD data, we are able to obtain mechanistic understanding of this reaction under a range of conditions.