TEM data for the first observation of quenched Davemaoite to Ambient Conditions: its Electron Diffraction Pattern

Calcium-rich silicate perovskite, davemaoite is often completely amorphized at ambient pressure, because the perovskite structure containing large element is unstable at 1 bar. However, we obtained for the first time an electron diffraction pattern of davemaoite in a transmission electron microscope. To understand why the unstable crystalline davemaoite lasted so long in the microscope, we investigate the textures with surrounding minerals using the electron-beam imaging and analyze the ambient volume from the diffraction patterns to understand the survival mechanisms. We find that the preservation of the crystalline state is most likely due to a static pressure generated by volume expansion of the surrounding amorphous glass transformed from the precursor denser crystalline state. The mechanism had not been demonstrated experimentally in a sub-micrometer microscopy before, even in the recovery of high-pressure minerals in shocked meteorites. Understanding this mechanism is important because the other high-pressure minerals at a small domain might survive at much lower pressure than the stability field at high pressure even though they are usually unquenchable. Further high-pressure minerals under a static stress can be discovered at ambient conditions by fine electron microscopy.