Comparative compressibility and equation of state of orthorhombic and tetragonal edingtonite

The high-pressure (HP) behaviour of a natural orthorhombic and tetragonal edingtonite from Ice River, Canada, has been investigated using in situ single-crystal X-ray diffraction. The two isothermal equations of state up to 6.74(5) GPa were determined. V0, KT0 and K′ refined with a third-order Birch-Murnaghan equation of state (BM-EoS) are: V0 = 598.70(7) Å3, KT0 = 59(1) GPa and K′= 3.9(4) for orthorhombic edingtonite and V0 = 600.9(2) Å3, KT0 = 59(1) GPa and K′= 4.2(5) for tetragonal edingtonite. The experiments were conducted with nominally hydrous pressure penetrating transmitting medium. No overhydration effect was observed within the pressure range investigated. At high-pressures the main deformation mechanism is represented by cooperative rotation of the secondary building unit (SBU). Si/A1 distribution slightly influences the elastic behaviour of the tetrahedral framework: the SBU bulk moduli are 125(8) GPa and 111(4) GPa for orthorhombic and tetragonal edingtonite, respectively. Extra-framework contents of both zeolites show an interesting behaviour under HP conditions: the split Ba2 site at P > 2.85 GPa is completely empty; only the position Ba 1 is occupied.