Long-Period Stacking Order of Oxygen Atoms Dissolved in α-Zirconium near the Composition ZrO_<1/3>

Ordered arrangements of oxygen atoms dissolved in α-zirconium near the stoichiometric composition ZrO_ have been investigated by means of electron diffraction and dark-field electron microscopy. The arrangements of oxygen atoms are specified as the long period stacking sequences of the interstitial layers of octahedral sites normal to the c axis of the h.c.p. lattice. Eight kinds of the stacking variants of the oxygen layers are found in the composition range from 24 to 26 at. % O in the order of 8H (71), 5H (41), 12R (31)_3, 7H (3121), 10H (131131), 9R (21)_3, 12H (13111131) and 14H (1131111311) or (1311111131). These stackings become irregular by quenching from about 600℃