Optimizing high-pressure pair distribution function measurements in diamond anvil cells

Pair distribution function (PDF) methods have great potential for the study of diverse high-pressure phenomena. However, the measurement of high-quality, high-resolution X-ray PDF data (to Q_max > 20 Å⁻¹) remains a technical challenge. An optimized approach to measuring high-pressure total scattering data for samples contained within a diamond anvil cell (DAC) is presented here. This method takes into account the coupled influences of instrument parameters (photon energy, detector type and positioning, beam size/shape, focusing), pressure-cell parameters (target pressure range, DAC type, diamonds, pressure-transmitting media, backing plates, pressure calibration) and data reduction on the resulting PDF. The efficacy of our approach is demonstrated by the high-quality, high-pressure PDFs obtained for representative materials spanning strongly and weakly scattering systems, and crystalline and amorphous samples. These are the highest-resolution high-pressure PDFs reported to date and include those for α-alumina (to Q_max  =  20 Å⁻¹), BaTiO₃ (to Q_max = 30 Å⁻¹) and pressure-amorphized zeolite (to Q_max  =  20 Å⁻¹).