Pitfalls and reproducibility of in situ synchrotron powder X-ray diffraction studies of solvothermal nanoparticle formation

In situ powder X-ray diffraction (PXRD) is a powerful characterization tool owing to its ability to provide time-resolved information about phase composition, crystal structure and microstructure. The application of high-flux synchrotron X-ray beams and the development of custom-built reactors have facilitated second-scale time-resolved studies of nanocrystallite formation and growth during solvothermal synthesis. The short exposure times required for good time resolution limit the data quality, while the employed high-temperature–high-pressure reactors further complicate data acquisition and treatment. Based on experience gathered during ten years of conducting in situ studies of solvothermal reactions at a number of different synchrotrons, a compilation of useful advice for conducting in situ PXRD experiments and data treatment is presented here. In addition, the reproducibility of the employed portable in situ PXRD setup, experimental procedure and data analysis is evaluated. This evaluation is based on repeated measurements of an LaB₆ line-profile standard throughout 5 d of beamtime and on the repetition of ten identical in situ synchrotron PXRD experiments on the hydrothermal formation of γ-Fe₂O₃ nanocrystallites. The study reveals inconsistencies in the absolute structural and microstructural values extracted by Rietveld refinement and whole powder pattern modelling of the in situ PXRD data, but also illustrates the robustness of trends and relative changes in the extracted parameters. From the data, estimates of the effective errors and reproducibility of in situ PXRD studies of solvothermal nanocrystallite formation are provided.