Superstructure and Order-Disorder Transformation of Interstitial Oxygen in Hafnium

概要

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Crystal structure and phase transition in the hafnium-oxygen system containing 10-20 at% O have been studied by means of electron, neutron and X-ray diffraction and calorimetry as well. The oxygen atoms occupy the octahedral holes in h.c.p. metal lattice and two types of interstitial superstructures are found at the hypo- and hyper-stoichiometric composition HfO_<1/6+> below 430℃. The lattice constants of the hexagonal supercells are respectively a=√<3>a_0, c=3c_0 and a=√<3>a_0, c=2c_0, where a_0 ∼3.2Å and c_0∼5.1Å are those of the metal lattice. The oxygen sublattices are described in terms of the stacking sequence of interstick layer parallel to the close-pack planes of the metal atoms, which varies continuously from A□B□C… for HfO_<1/6-> to A□B□… for HfO_<1/6+>. The concentration dependence of the ordered structures is interpreted in terms of strain ordering.
社団法人日本物理学会の論文
1973-08-05