High pressure phase transitions of paracelsian BaAl₂Si₂O₈.

ABSTRACT: Three new polymorphs of aluminosilicate paracelsian, BaAl₂Si₂O₈, have been discovered using synchrotron-based in situ high-pressure single crystal X-ray diffraction. The first isosymmetric phase transition (from paracelsian-I to paracelsian-II) occurs between 3 and 6 GPa. The phase transition is associated with the formation of pentacoordinated Al³⁺ and Si⁴⁺ ions, which occurs in a stepwise fashion by sequential formation of Al-O and Si-O bonds additional to those in AlO₄ and SiO₄ tetrahedra, respectively. The next phase transition occurs between 25 and 28 GPa and is accompanied by the symmetry change from monoclinic (P2₁/c) to orthorhombic (Pna2₁). The structure of paracelsian-III consists o

SUBMITTER: Gorelova LA 

PROVIDER: S-EPMC6718520 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature