Long-term stability of the Fm-3m-LaH10 crystal lattice.

X-ray powder diffraction patterns of LaH10 (sample IV) measured 55 months after synthesis. Pressure was determined to160 GPa using H2 Raman vibron scale and 175 GPa using diamond edge Raman scale. Monochromatic x-rays with wavelength of 0.3738 Å and a spot size of 0.7 x 0.7 μm^2 were used and diffraction collected with a Eiger2 CdTe 9M detector. Detector distance was calibrated using CeO2 standard from NIST to 0.192146 m. Data set "CeO2_eigx190" contains the calibration and scan 1 contains the relevant diffraction pattern. "QF153" is the actual measurement, were scans 1-7 are alignment scans with transmitted x-ray intensity recorded on photodiode 3. Scans 9 and 10 contain x-ray diffraction recorded on mesh scans across the sample.