Study of phase transitions in A3MO3F3 compounds (A = K, Rb, Cs; M = Mo, W)

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.…”

K2SnOF4 and K2WO3F2 – different but similar

“…It is less common to observe main group elements within these compounds. For oxidofluoridotungstanates different octahe-dral units have been reported in the literature, e.g., the [WO 4 F 2 ] 4− unit observed within Cs 2 WO 3 F 2 or Ba 2 WO 3 F 4 , the [WO 3 F 3 ] 3− unit observed within K 3 WO 3 F 3 , the [WO 2 F 4 ] 2− unit observed within K 3 HF 2 WO 2 F 4 and A 2 WO 2 F 4 (A = NH 4 , Na, Rb, Cs), and the [WOF 5 ] − unit observed within K 3 WOF 7 , Ag(WOF 5 ) 2 , and (XeF 2 )(WOF 4 ) [2][3][4][5][6][7][8][9][10][11][12][13]. Some of these units, as well as other oxidofluoridometallates exhibiting similar units, recently gained some attention because of the possibility for partial substitution with Mn 4+ which can produce materials exhibiting red luminescence upon blue light excitation [6][7][14][15][16][17][18].…”

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

“…K MoO F undergoes a series of reversible structural phase transitions on cooling from this high-temperature ideal cubic polymorph. The typical transition sequence for the A> B>M4'O F (A, B"K, Rb, Cs; M4'"Mo, W) family of elpasolite-related phases (6}11), particularly when the A and B cations are of the same type (9), is from a highest temperature, ideal cubic (Fm3 m) polymorph (above ¹ ) through an intermediate (ferroelectric and also reported to be ferroelastic) polymorph (¹ (¹(¹ ) to a low-temperature (ferroelectric as well as ferroelastic) polymorph (below a transition temperature ¹ which is usually above room temperature). (In the case of K MoO F these transition temperatures correspond to ¹ "436 K and ¹ "522 K, respectively (9)).…”