An electron diffraction and XRPD study of superlattice ordering in the elpasolite-related oxyfluoricle K3MoO3F3

A detailed electron diffraction and XRPD study has been made of the room-temperature a polymorph of K3MoO3F3. It is shown that the true Symmetry of (his polymorph is neither tetragonal, trigonal, nor triclinic as previously reported but rather monoclinic I1a1, a = 2a(p) - c(p), b = 4b(p), c = a(p) + 2c(p) when expressed in terms of the underlying elpasolite (ordered perovskite) parent structure type. A highly structured, three-dimensional, continuous diffuse intensity distribution (presumably, arising from local O/F ordering and associated structural relaxation) is shown to coexist with the sharp satellite reflections characteristic of the monoclinic supercell. (C) 2002 Elsevier Science.