High-pressure behavior of davyne [CAN-topology] : an in situ single-crystal synchrotron diffraction study

The high-pressure elastic behavior and the pressure-induced structural evolution of a natural P63/m davyne was investigated by in situ single-crystal synchrotron diffraction with a diamond anvil cell. A P-induced displacive phase transition from a P63/m to a P63 structure occurred between room-P and 0.38(2) GPa. The post-transition P6 3-davyne showed a large isothermal (293 K) stability field as function of pressure, being stable at least up to 7.18(2) GPa. The elastic behavior was described by a III-order Birch-Murnaghan equation of state fit, leading to the following refined elastic parameters: V0 = 761.6(5) Å3, KV0=46.5(11)GPa and KV′=3.7(3); a 0 = 12.814(2) Å, Ka0=50.3(9)GPa and Ka′=4.0(3); c0 = 5.3561(9) Å, Kc0=40.3(7)GPa and Kc′=3.2(2). The refined isothermal volume bulk modulus (46.5(3) GPa) is comparable to those so far reported for other cancrinite-group compounds. The elastic anisotropy at room-P conditions can be described as K a0:Kc0=1.25:1, and was found to increase with pressure. The bulk volume compression is mainly accommodated by the tilting of the quasi-rigid framework tetrahedra. A description of the P-induced deformation mechanisms at the atomic scale and a comparison with the pressure-induced behavior of previously studied cancrinite-group minerals are carried out.