Extended Data Fig. 2: Schematic diagram of the high-pressure cell used in the present ultrasonic experiments.

Buffer rod, Al₂O₃; sample, CaSiO₃ glass (Fig. 1a); pressure marker, NaCl and BN; soft medium, MgO; pressure medium, (Mg,Co)O; insulator, LaCrO₃. ⊗ denotes the thermocouple hot junction.