Paraelectric–paraelastic Rb₂KMoO₃F₃ structure at 343 and 473 K

Raman spectroscopic study of the lattice dynamics in the Rb2KMoO3F3 oxyfluoride

“…In [2,[11][12][13][14]18], it was found that the Rb 2 KMoO 3 F 3 elpasolite undergoes two successive phase transitions at T = 328 K (with appearance of a spontaneous polarization) and at T = 182 K. The stud ies of the compound were restarted several years ago. In [17], the properties of the Rb 2 KMoO 3 F 3 elpasolite were studied on many samples synthesized by various methods.…”

“…Depending on the ratio of the ionic radii R A and R A' and also on the type of M atoms, the structure can be distorted as a result of two [7][8][9][10][11][12][13][14][15] or one phase transition [1,7,[11][12][13][14]16], or it can remain stable down to the liquid helium temperature [7,[11][12][13][14]. For instance, despite very close values of the ionic radii of Mo (R Mo = 0.073 nm) and W (R W = 0.074 nm) atoms, the Rb 2 KMoO 3 F 3 elpasolite undergoes a phase transition on cooling [17], while the Rb 2 KWO 3 F 3 elpasolite remains cubic and does not undergo any phase transformations.…”

An Electron Diffraction and XRPD Study of Superlattice Ordering in the Elpasolite-Related Oxyfluoride K3MoO3F3

“…K MoO F is one member of the rather large subgroup of oxy#uoride phases (A> B>M'4OF (A, B"an alkali ion; M'4"Ti, V), A> B>M4O F (A, B"alkali; M4"V, Nb), and A> B>M4'O F (A, B"K, Rb, Cs; M4'"Mo, W)) (3, 4) which belong to this group. Despite the two chemically distinct anion species in the case of the latter oxy#uoride subgroup, there has to date been no evidence for oxygen/#uorine ordering in any of these phases (as is also the case for many other oxy#uoride systems (5)); i.e., random anion site disorder has invariably been reported for the anion, or X, site positions (3,6).…”

A combined diffraction (XRD, electron and neutron) and electrical study of Na3MoO3F3

“…When the alkali element in the interstitial, nominally 12-coordinate, A cation site (see Fig.1) is K, Rb, Tl or Cs (A = K, Rb, Tl or Cs), the metric symmetry of the underlying parent sub-structure reported for the intermediate β polymorph (as well as for the lower temperature α polymorphs, despite the often complicating presence of additional satellite reflections) has invariably been tetragonal or pseudo-tetragonal (1- 6,[12][13][14]. (Note that the strongest reflections in all polymorphic forms are those corresponding to the F-centred parent substructure, labelled with the subscript p in what follows).…”