OD (order-disorder) character of the crystal structure of godlevskite Ni9 S8

Abstract

Godlevskite Ni 9 S 8 has been found to be an OD (order-disorder) structure consisting of two kinds of OD layers in strict alternation; these layers display stacking disorder. They have layer symmetries P (4)2 m and P 2 1 2(2), respectively (symmetry elements in parentheses are perpendicular to OD layers). Two structures with maximum degree of order (MDO polytypes), with space-group symmetries A 222 and I 4 1 22, respectively, exist, together with more complex polytypes or disordered sequences. The OD character is in keeping with the frequent twinning of godlevskite.