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 P6(3)/m davyne was investigated by in situ single-crystal synchrotron diffraction with a diamond anvil cell. A P-induced displacive phase transition from a P6(3)/m to a P6(3) 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: V-0 = 761.6(5) angstrom(3), K-v0 = 46.5(11) GPa and K'(v) = 3.7(3); alpha(0) = 12.814(2) angstrom, K-alpha 0 = 50.3(9) GPa and K-alpha' = 4.0(3); c(0) = 5.3561(9) angstrom, Kc(0) = 40.3(7) GPa and K-c' = 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-alpha 0 : K-c0 = 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. (C) 2014 Elsevier Inc. All rights reserved.