Crystal growth and structural investigation of A2BReO6 (A=Sr, Ba; B=Li, Na)

Structural investigation of Sr2LiReO6. Evidence for a continuous tetragonal–cubic phase transition

“…The narrowness of the diffraction peaks demonstrates the sample to be highly crystalline and there is no evidence from this diffraction pattern for any crystalline impurities. Refinement in the tetragonal I4/m system yielded lattice parameters of a ¼ 5.55033(4) and c ¼ 7.92269(7) Å in good agreement with those reported by Bharathy and zur Loye [5] (a ¼ 5.5467(2) and c ¼ 7.9197(4) Å ). The average Re-O (1.846 Å ) and Li-O (2.124 Å ) bond distances derived from the refinement are chemically reasonable, the Re-O distance being comparable to the values reported for the various A 2 BReO 6 oxides studied using single crystal X-ray methods [5].…”

“…That the polycrystalline sample of Sr 2 LiReO 6 was tetragonal at room temperature, as described by Bharathy and zur Loye [5], was immediately obvious from inspection of the powder X-ray diffraction pattern, Fig. 1.…”

“…A group theoretical analysis of the possible structures in double perovskites shows that a Fm3m-I4/ m transition is allowed to be continuous [6]. The report by Bharathy and zur Loye [5] that these two structures can be obtained for Sr 2 LiReO 6 at room temperature and that these do not show a continuous temperature dependent phase transition is clearly anomalous and worthy of further investigation.…”

“…The rhenate double perovskites A 2 BReO 6 were first described by Sleight et al [3,4] almost 50 years ago, and re-investigation of these using modern physical methods has been particularly fruitful. Very recently Bharathy and zur Loye [5] reported the crystal growth and structural characterisation of some rhenate double perovskites where the B-type cation was an alkali metal (Li or Na). In particular they reported that whereas single crystals of Sr 2 LiReO 6 were cubic, powder samples of the same composition were tetragonal and the measurements reported in this paper suggested that once formed these two structures apparently did not interconvert [5].…”

“…Very recently Bharathy and zur Loye [5] reported the crystal growth and structural characterisation of some rhenate double perovskites where the B-type cation was an alkali metal (Li or Na). In particular they reported that whereas single crystals of Sr 2 LiReO 6 were cubic, powder samples of the same composition were tetragonal and the measurements reported in this paper suggested that once formed these two structures apparently did not interconvert [5]. This observation is unexpected.…”