Compact high-pressure cell for <i>in situ</i> synchrotron powder x-ray diffraction featuring precise pressure and temperature control and a wide aperture for crystallographic studies under pressures of up to 400 MPa

High-pressure conditions in the megapascal range are critical in industrial material synthesis, food science, and biospheric Earth science. However, in situ measurements for analyzing material behavior under such conditions remains challenging because of the difficulty of precise pressure-temperature control and high-Q-range data acquisition. To overcome these limitations, we developed a compact high-pressure cell for synchrotron x-ray diffraction, enabling crystal structural analysis at pressures up to 400 MPa and temperatures up to 180°C. The cell provides a wide downstream aperture angle of 72°, substantially larger than those of conventional cells, and is optimized for wide-angle diffraction necessary for crystallographic studies. Using water as the pressure medium, the system allows fine pressure adjustments in 0.1 MPa increments via a manual pump, while a pressure transducer enables real-time monitoring without the need for pressure markers. Temperature is controlled with cartridge heaters and monitored by a thermocouple positioned near the sample. Validation experiments using compressibility, phase transitions, and freezing point determination helped confirm the high accuracy of the results, with the absolute errors in the pressure and temperature being below 10 MPa and 1.5°C, respectively. A Rietveld refinement of NaCl diffraction data at 400 MPa yielded low R-factors, confirming the reliability of the cell for crystal structural analysis. Powdered samples were sealed in polyimide tubes or tapes, facilitating rapid and disposable sample exchange while accommodating soluble, hygroscopic, deliquescent, or anaerobic materials. The cell can support hydrostatic and uniaxial compressions by selecting the sample packing method, offering versatility in a single apparatus.