Fig. 1. Routine set-up for high-pressure SCXRD at PX², including a monochromated x-ray beam (0.4340 Å in wavelength and 12 × 18 µm² in beam size), a Pilatus3S 1M area detector, an online ruby fluorescence system, and a membrane system for remote pressure control. The φ rotation is applied to the six-circle diffractometer.

Fig. 2. (a) Microphotograph of sample chamber after gas-loading with neon, including three ilvaite crystals and a ruby sphere. (b) Diffraction image of ilvaite collected at 20.6(2) GPa. (c) and (d) Diffraction peaks of ilvaite collected at 20.6(2) and 22.8(2) GPa, respectively, in the area outlined by the red box in (b). The peaks of two crystal domains in (d) are differentiated by different colors.

Fig. 3. Crystal structures of (a) ilvaite-I, (b) ilvaite-II, and (c) ilvaite-III viewed along the c axis. The red balls indicate oxygen atoms. The unit-cell edges are indicated by black frames.

Fig. 4. Unit-cell parameters of ilvaite as functions of pressure: (a) a; (b) b; (c) c; (d) β.

Fig. 5. (a) Unit-cell volume of ilvaite as a function of pressure. The solid lines represent a BM3 EoS fitting of the data (ilvaite-I and ilvaite-II), and the dashed lines represent an extrapolation. The EoS parameters K_T0 and KT0′ are also shown. (b) F_E–f_E plot of ilvaite.

Fig. 6. Interatomic distances in the ilvaite structure as functions of pressure: (a) Ca–O; (b) Si1–O; (c) Si2–O. The pressure ranges of ilvaite-I, ilvaite-II, and ilvaite-III are indicated by white, gray, and red shaded regions, respectively.

Fig. 7. Interatomic distances in the ilvaite structure as functions of pressure: (a) Fe11–O; (b) Fe12–O; (c) Fe2–O. The pressure ranges of ilvaite-I, ilvaite-II, and ilvaite-III are indicated by white, gray, and red shaded regions, respectively.

Fig. 8. Polyhedral distortion indices of CaO₇, Si1O₄, Si2O₄, Fe11O₆, Fe12O₆, and FeO₆ in the ilvaite structure as functions of pressure. The pressure ranges of ilvaite-I, ilvaite-II, and ilvaite-III are indicated by white, gray, and red shaded regions, respectively.