High-pressure study of a natural cancrinite

Abstract

The high-pressure elastic behavior and the P-induced structure evolution of a natural cancrinite from Cameroun {Na 6.59 Ca 0.93 [Si 6 Al 6 O 24 ](CO 3 ) 1.04 F 0.41 ·2H 2 O, 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 á = 4.5(9), for the a-axis, and c 0 = 5.112(3) Å, K c0 = 36(1) GPa, K ć = 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.

Thermoelastic behavior and dehydration process of cancrinite

“…The in-situ high-temperature X-ray diffraction experiment was performed on a crystal fragment (size 300 x 200 x 150 μm 3 ), from the main batch already used by Della Ventura et al (2009 and Lotti et al (2012), showing sharp optical extinction with crossed polarized light under the microscope. The previous diffraction studies reported no superstructure reflections.…”

“…In order to get a stable refinement, some restraints were applied: i) the Na2/Ca2 site was refined applying a mixed Na/Ca X-ray scattering curve and constraining their fractions to sum full occupancy (a test refinement with occupancy factors free to vary validated this as a good approximation, i.e. within 2); ii) the C1-OC1 and C2-OC2 bond distances were restrained to 1.300(5) Å following a previously reported procedure Lotti et al 2012); iii) the C1-C2 and OC1-OC2 sites were constrained to share the same displacement parameters (dp's), respectively. Convergence was achieved in the last cycles of refinement with anisotropic dp's for all the sites, excluding Ow.…”

“…A single-crystal high-T X-ray diffraction study of cancrinite was performed by Isupova et al (2010), in order to investigate the asymmetric probability density function of the atomic sites, for the calculation of the pyroelectric coefficients. Recently, Lotti et al (2012Lotti et al ( , 2014 investigated the high-pressure behavior of cancrinite and balliranoite by in-situ single-crystal X-ray diffraction (SC-XRD) under hydrostatic conditions up to about 7 GPa. For the experiment on cancrinite, Lotti et al (2012) used a fragment from the same gem-quality sample from Cameroun previously used by Della Ventura et al (2009) for single-crystal FTIR and neutron diffraction experiments.…”

“…Recently, Lotti et al (2012Lotti et al ( , 2014 investigated the high-pressure behavior of cancrinite and balliranoite by in-situ single-crystal X-ray diffraction (SC-XRD) under hydrostatic conditions up to about 7 GPa. For the experiment on cancrinite, Lotti et al (2012) used a fragment from the same gem-quality sample from Cameroun previously used by Della Ventura et al (2009) for single-crystal FTIR and neutron diffraction experiments. A single-crystal from the same sample was also studied at low temperature (T ≤ 293 K) by in-situ X-ray diffraction .…”

“…A single-crystal from the same sample was also studied at low temperature (T ≤ 293 K) by in-situ X-ray diffraction . Gatta et al (2012) and Lotti et al (2012) reported the low-T and high-P thermoelastic behavior of cancrinite and its lowT-and P-induced structural evolution, with a description of the main deformation mechanisms, which turned to be similar though with a different magnitude. Very recently, Kurdakova et al (2013) have performed a study on the thermodynamic properties of synthetic calcium-free cancrinite, reporting new values of the heat capacity, third-law absolute entropy, enthalpy and Gibbs free energy of formation.…”