Reinvestigation of KMg1/3Nb2/3OPO4Dedicated to Professor Nikolay S. Slobodyanik on the occasion of his 65th birthday.

Abstract

The crystal structure of potassium magnesium niobium oxide phosphate, KMg1/3Nb2/3OPO4, which was described in the space group P4322 [McCarron & Calabrese, (1993). J. Solid State Chem. 102, 354–361], has been redetermined in the revised space group P41. Accordingly, the assignment of the space group P4322 and, therefore, localization of K at a single half-occupied position, as noted in the previous study, proved to be an artifact. As a consequence, two major and two minor positions of K are observed due to the splitting along [001], as first noted for KTiOPO4 structure analogues. It has been shown that the geometry of the {MII1/3Nb2/3O6/2}∞ framework is almost unaffected by the lowering of symmetry.