Department of Earth and Planetary Science, Faculty of Science, Kyoto University, Kitashirakawa-Oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
J Phys Condens Matter. 2010 Jun 9;22(22):225402. doi: 10.1088/0953-8984/22/22/225402. Epub 2010 May 12.
For molecular dynamics simulations using aragonite structure as the initial state, a new phase of space group P6₃22 (hexagonal aragonite) appeared at temperatures above 510 K at a pressure of 1 atm. It was a first-order phase transition which occurs metastably within the stable region of calcite and the dT/dP slope of the phase boundary between orthorhombic and hexagonal aragonite was about 1.25 × 10³ K GPa⁻¹. In the hexagonal aragonite structure, CO₃ groups were rotated by 30° around the c axis and move up and down along the c axis from their position in aragonite, and Ca ions were six-coordinated as they are in calcite. The CaO₆ octahedron of hexagonal aragonite was strongly distorted, whereas in the calcite structure it is an almost ideal octahedron. The transition between hexagonal and orthorhombic aragonite involves only small movements of CO₃ groups. Therefore, it is possible that hexagonal aragonite plays an important part in the metastable formation of aragonite within the stability field of calcite and in the development of sector trilling in aragonite.
对于使用方解石结构作为初始状态的分子动力学模拟，在 1 大气压下，温度高于 510 K 时，出现了空间群 P6₃22（六方文石）的新相。这是一个一级相变，在方解石的稳定区域内亚稳存在，并且正交相和六方相之间的相边界的 dT/dP 斜率约为 1.25×10³ K GPa⁻¹。在六方文石结构中，CO₃基团围绕 c 轴旋转 30°，并沿着 c 轴从文石中的位置上下移动，Ca 离子与方解石中的一样，六配位。六方文石的 CaO₆八面体强烈扭曲，而在方解石结构中，它几乎是理想的八面体。六方相和正交相之间的转变只涉及 CO₃基团的微小移动。因此，六方文石在方解石稳定场中方解石亚稳形成和文石扇形颤振发育中可能起着重要作用。
