Abstract Cubic perovskite-type CaSiO3 known as davemaoite, space group Pm3¯m, is considered to be the third most abundant mineral in Earth’s lower mantle. However, davemaoite is difficult to preserve as large domains due to amorphization upon recovery to ambient conditions, which limits direct investigation of its intrinsic properties. Ti-bearing calcium silicate can appear in a subducting basaltic crust and also serves as a quenchable analogue of davemaoite, providing an important opportunity to investigate the structural behavior and physical properties of davemaoite under lower mantle conditions. Here three quenchable Ti-bearing calcium silicate samples, CaSi0. 53Ti0. 47O3, CaSi0. 58Ti0. 40Al0. 02O3, and CaSi0. 59Ti0. 41O3, were synthesized at high pressure and temperature conditions using a Kawai-type multi-anvil press. Their crystal structures, microstructures, and vibrational characteristics were investigated by single-crystal X-ray diffraction, transmission electron microscopy, and Raman spectroscopy, respectively. Structure refinements revealed that they crystallized in the orthorhombic perovskite structure (space group Pbnm). Twinning was observed in all samples, with 112 reflection twins identified via single-crystal X-ray diffraction and precession selected area electron diffraction. Twinning in Ti-bearing calcium silicate perovskites may originate from a phase transformation from a high-temperature cubic or tetragonal symmetry to a low-temperature orthorhombic symmetry during temperature quenching at high pressure. Raman spectrum of CaSi0. 53Ti0. 47O3 exhibits vibrational features similar to that of the orthorhombic CaTiO3 perovskite, but differs from those of CaSi0. 58Ti0. 40Al0. 02O3 and CaSi0. 59Ti0. 41O3. The difference in Raman spectra is likely related to the enhancement of overtone signals due to the polycrystalline nature of the CaSi0. 58Ti0. 40Al0. 02O3 and CaSi0. 59Ti0. 41O3 samples with respect to the large crystal of CaSi0. 53Ti0. 47O3. This study contributes to resolving the long-standing debate over the crystal structure of CaSi1-xTixO3 and provides new insights into the phase relations within the CaSiO3-CaTiO3 system.
Wu et al. (Wed,) studied this question.