Search

The high-temperature structural properties of solid benzene were studied at 1.5–8.2 GPa up to melting or decomposition using multianvil apparatus and in situ neutron and X-ray diffraction. The crystal structure of deuterated benzene phase II (P21/c unit cell) was refined at 3.6–8.2 GPa and 473–873 K. Our data show a minor temperature effect on the change in the unit cell parameters of deuterated benzene at 7.8–8.2 GPa. At 3.6–4.0 GPa, we observed the deviation of deuterium atoms from the benzene ring plane and minor zigzag deformation of the benzene ring, enhancing with the temperature increase caused by the displacement of benzene molecules and decrease of van der Waals bond length between the π-conjuncted carbon skeleton and the deuterium atom of adjacent molecule. Deformation of benzene molecule at 723–773 K and 3.9–4.0 GPa could be related to the benzene oligomerization at the same conditions. In the pressure range of 1.5–8.2 GPa, benzene decomposition was defined between 773–923 K. Melting was identi...

Doping large amounts of a incompatible element into calcite, a polymorph of CaCO3, was achieved by pressurizing amorphous calcium carbonate (ACC) containing a dopant. Strontium-doped ACC samples were prepared from supersaturated solutions. ACC was transformed to calcite at 0.8 GPa and 25 °C. The lattice volume of calcite obtained by pressurizing ACC increased monotonically up to 372.5 A3 (1.3% increase from a Sr-free sample) with increasing Sr content in ACC up to 0.15 in Sr/(Sr + Ca). For comparison, the lattice volumes of calcite samples precipitated from supersaturated CaCO3 solution containing Sr were obtained, but the lattice volume of calcite precipitated from supersaturated solutions showed no noteworthy increase. Results of this study indicate that pressure-induced crystallization is an efficient pathway to dope incompatible elements into crystals.

This report describes a newly observed phenomenon: pressure-induced crystallization from amorphous calcium carbonate (ACC). Synthetic ACC samples were pressurized up to 800 MPa at room temperature. Then crystallization of vaterite and calcite was observed from X-ray diffraction patterns. The crystallization pressure depends on the H2O contents of ACCs. The ACC samples with high-H2O content (21 wt %), middle-H2O content (17 wt %), and low-H2O content (10 wt %) underwent crystallization at pressures higher than 240 MPa, 400 MPa, and 640 MPa, respectively. These results indicate that H2O in the ACC serves an important role in the crystallization process and that we should treat ACC carefully in preparation for analyses such as infrared spectroscopy to obtain the intrinsic information related to amorphous materials.