含水鉱物の相転移における水素結合の役割

抄録

  Here I briefly review the results of crystallographic studies for high pressure phases of aluminum hydroxides, δ-AlOOH and δ-Al(OD)₃ by using X-ray and neutron diffraction. The neutron diffraction study for δ-AlOOH and δ-(Al_0.86Mg_0.07Si_0.04)OOH resolved the long-standing problem of the symmetry of this phase. The observed reflection conditions clearly show that the space group of pure δ-AlOOH is P2₁nm with ordered hydrogen bonds, whereas that of δ-(Al_0.86Mg_0.07Si_0.04)OOH is Pnn2 or Pnnm with disordered hydrogen bonds. The space group of δ-Al(OD)₃ was first reported as Pnam with disordered hydrogen bonds by powder X-ray diffraction, but it was subsequently revised to P2₁2₁2₁ with ordered hydrogen bonds by the neutron diffraction study. From the viewpoint of polyhedra and hydrogen bond network, I present how their symmetry and order-disorder state of hydrogen are related to the polyhedra in their crystal structures.