Toudic Bertrand, Garcia Pilar, Odin Christophe, Rabiller Philippe, Ecolivet Claude, Collet Eric, Bourges Philippe, McIntyre Garry J, Hollingsworth Mark D, Breczewski Tomasz
Universitéde Rennes 1, Institut de Physique de Rennes (IPR), 35042 Rennes Cedex, France.
Science. 2008 Jan 4;319(5859):69-71. doi: 10.1126/science.1146745.
Numerous crystalline materials, including those of bioorganic origin, comprise incommensurate sublattices whose mutual arrangement is described in a superspace framework exceeding three dimensions. We report direct observation by neutron diffraction of superspace symmetry breaking in a solid-solid phase transition of an incommensurate host-guest system: the channel inclusion compound of nonadecane/urea. Strikingly, this phase transition generates a unit cell doubling that concerns only the modulation of one substructure by the other-an internal variable available only in superspace. This unanticipated pathway for degrees of freedom to rearrange leads to a second phase transition, which again is controlled by the higher dimensionality of superspace. These results reveal nature's capacity to explore the increased number of phases allowed in aperiodic crystals.
许多晶体材料，包括那些生物有机来源的材料，都包含不相称子晶格，其相互排列在超过三维的超空间框架中描述。我们报告了通过中子衍射对一种不相称主客体系统（十九烷/尿素的通道包合物）在固-固相变中超空间对称性破缺的直接观察。引人注目的是，这种相变产生了晶胞加倍，这只涉及一个子结构对另一个子结构的调制——这是一个仅在超空间中可用的内部变量。这种自由度重新排列的意外途径导致了第二次相变，而这同样由超空间的更高维度控制。这些结果揭示了自然界探索非周期性晶体中允许的更多相的能力。
