Abstract
Pressure-induced phase transitions from the zircon structure-type (I41/amd) to the scheelite structure type (I41/a) are known for many ternary oxides systems (ABO4). In this work, we present the first high-pressure study on synthetic stetindite (CeSiO4) by a combination of in situ high-pressure synchrotron powder X-ray diffraction up to 36 GPa, implemented with and without dual sided laser heating, and in situ high-pressure Raman spectroscopy up to 43 GPa. Two phase transitions were identified: zircon to a high-pressure low-symmetry (HPLS) phase at 15 GPa and then to a scheelite at 18 GPa. The latter from HPLS scheelite phase was found irreversible; i.e., scheelite is fully quenchable at ambient conditions, as in other zircon-type phases. The bulk moduli (K0) of stetindite, HPLS, and high-pressure scheelite phases were determined, respectively, as 171(5), 105(4), and 221(40) GPa by fitting to a second-order Birch–Murnaghan equation of state. The pressure derivatives of vibrational modes and Grüneisen parameters of the zircon-structured polymorph are similar to those of other orthosilicate minerals. Due to the larger ionic radii of Ce4+, with respect to Zr4+, stetindite was found to possess a softer bulk modulus and undergo the phase transitions at a lower pressure than zircon (ZrSiO4), such observations are consistent with what were found in coffinite (USiO4).