Characterization of quenched high pressure phases in CaSiO3 system by XRD and 29Si NMR

We have studied quenched high pressure phases in the CaSiO3 system by x‐ray diffraction (XRD) and 29Si MAS NMR, XRD study of the previously reported “ε‐CaSiO3 phase” synthesized at 12 GPa and 1500 °C reveals that it is actually a mixture of β‐Ca2SiO4 (larnite) and a previously unknown CaSi2O5 phase. This result is supported by the 29Si NMR spectra. Furthermore, both the XRD and the NMR data suggest that the CaSi2O5 phase may have a titanite (CaTiSiO5) structure in which Ti is replaced by an octahedral Si. Samples quenched from 15 GPa and 1500°C consist mostly of an amorphous phase, but a small amount of CaSiO3‐perovskite was identified by both XRD and NMR. The 29si NMR spectrum of the amorphous phase suggests that its local structure is similar to that of a glass quenched from melt at 1 bar.