High-pressure study of a natural cancrinite

The high-pressure elastic behavior and the P-induced structure evolution of a natural cancrinite from Cameroun {Na 6.59Ca 0.93[Si 6Al 6O 24](CO 3) 1.04F 0.41·2H 2O, a = 12.5976(6) Å, c = 5 .1168(2) Å, space group: P6 3} were investigated by in situ single-crystal X-ray diffraction under hydrostatic conditions up to 6.63(2) GPa with a diamond-anvil cell. The P-V data were fitted with an isothermal Birch-Murnaghan type equation of state (BM EoS) truncated to the third order. Weighted fit (by the uncertainty in P and V) gave the following elastic parameters: V 0 = 702.0(7) Å 3, K V0 = 51(2) GPa, and K' v = 2.9(4). A linearized BM EoS was used to fit the a-P and c-P data, giving the following refined parameters: a 0 = 12.593(5) Å, K a0 = 64(4) GPa, K' a = 4.5(9), for the a-axis, and c 0 = 5.112(3) Å, K c0 = 36(1) GPa, K' c = 1.9(3) for the c-axis (elastic anisotropy: K a0:K c0 = 1.78:1). A subtle change of the elastic behavior appears to occur at P > 4.62 GPa, and so the elastic behavior was also described on the basis of BM EOS valid between 0.0001-4.62 and 5.00-6.63 GPa, respectively. The high-pressure structure refinements allowed the description of the main deformation mechanisms responsible for the anisotropic compression of cancrinite on (0001) and along [0001]. A comparative analysis of the structure evolution in response of the applied pressure and temperature of isotypic materials with cancrinite-like topology is carried out.