Crystal structures and phase transition behaviour in the 5d transition metal oxides AReO₄ (A = Ag, Na, K, Rb, Cs and Tl)

Abstract

The structures of the six perrhenates (AReO4 A = Ag, Na, K, Rb, Cs and Tl) at RT and the phase transitions associated with change in the orientation of the ReO4− tetrahedra seen for A = Rb, Cs and Tl are described.

Structural and Magnetic Studies of ABO4-Type Ruthenium and Osmium Oxides

“…This behavior is very similar to that reported recently for CsTcO 4 and CsReO 4 . 7,22 CsOsO 4 rapidly decomposed above 600 K. The decomposition of this, and of the other Ru and Os oxides studied here, at high temperatures contrasts that seen for the ATcO 4 and AReO 4 compounds, where the room temperature structures can be recovered from the high temperature melts upon cooling. 7 As anticipated from the heat capacity measurements, CsOsO 4 undergoes a second phase transition upon cooling, see Figure 8.…”

“…RbOsO 4 displays anomalous thermal expansion behavior associated with a continuous I4 1 /a to I4 1 /amd transition as seen recently in both RbTcO 4 and RbReO 4 . 12,22 While the high temperature phase transition behavior seen for CsOsO 4 is similar to that observed in the isostructural Tc and Re oxides, the first order transition observed upon cooling has no analogy in these oxides, rather it involves a reconstructive transition to a new P2 1 /c polymorph rather than the I2/a fergusonite structure observed in oxides such as LaNbO 4 . 42 At room temperature CsRuO 4 has a structure that is more closely related to baryte (BaSO 4 ) than scheelite.…”

“…We have recently demonstrated for the analogous A ReO 4 oxides that in tetragonal scheelite-type structures the distortion of the B O 4 tetrahedra correlates with the size of the A -type cation with the bond angles moving away from the ideal value of 109° as the size of the A -cation increases . This trend is followed for the pair of oxides KOsO 4 and RbOsO 4 .…”

“…The temperature dependence of the c parameter is very similar to what we described recently for RbTcO 4 and RbReO 4 where it was established that the change was due to a softening at the Γ point resulting in a I4 1 /amd to I4 1 /a phase transition. 7,22 These two structures differ in their orientation of the BO 4 tetrahedra; in I4 1 /a the tetrahedra are rotated about the c-axis, see Figure 7, and the x parameter for the oxygen in the general position 16f is a variable, whereas this is constrained to x = 0 for the equivalent 16h position in l4 1 /amd. The cations are on special positions in both structures.…”

Sr[ReO4]2: The First Single Crystals of an Anhydrous Alkaline‐Earth Metal Meta‐Perrhenate

“…[ 4 ] However, even though the high chemical and thermal stability of perrhenates lead to easy handling compared to the other alkaline‐earth metal oxometalates(VII), [ 5 ] there is a surprising lack of structure data in some areas. Even though there are recent reports on anhydrous alkali metal meta ‐perrhenates A [ReO 4 ] ( A = Na – Cs), [ 6 ] no structural data on anhydrous alkaline‐earth metal meta ‐perrhenates have been reported up to now with the exception of some mixed cationic ones, like for example CaNa[ReO 4 ] 3 . [ 7 ] However, Jeitschko et al did excellent work on ortho ‐perrhenates (e.g.…”