In situ ptychographic x-ray nanotomography of temperature-controlled crystallization processes.

Dynamic processes such as crystallization, sintering and phase separation play pivotal roles in defining the structure and performance of engineered and natural materials. Yet, these phenomena are often challenging to study because they are transient, spatially heterogeneous, and span multiple length and time scales. Visualizing them in three dimensions under realistic conditions therefore requires imaging techniques capable of probing representative sample volumes with nanoscale resolution and minute-scale temporal resolution, sustained over extended observation times and across a wide range of environmental conditions, capabilities that current in situ methods rarely combine. Here, we present an integrated platform for in situ time- and temperature-resolved ptychographic X-ray nanotomography that meets these demands, and demonstrate its capability by tracking the crystallization of amorphous calcium carbonate from room temperature to 500°C. Quantitative tomograms are acquired at five-minute intervals, producing a 4D dataset that reveals multiple simultaneous crystallization pathways, and rare and transient events. Among these is the formation and recrystallization of a metastable polymorph, calcium carbonate hemihydrate, which has previously only been observed in additive-stabilized systems. We also demonstrate how volume defect evolution and structural rearrangements within individual crystals contribute to the mechanisms underlying Ostwald ripening. This platform offers a general method for in situ visualization of material transformations, providing insights into the processes that govern material structure and functionality.