Structural studies of the phases in Ba2LaIrO6—New light on an old problem

On the symmetry and crystal structures of Ba2LaIrO6

“…The later finding has been confirmed by Kockelmann et al using highresolution time-of-flight neutron powder diffraction data [13]. However, we have noticed a recent paper by Zhou et al [14] who investigated, once again, the structure of Ba 2 LaIrO 6 . In their paper they claimed that Ba 2 LaIrO 6 crystallizes in R3 at above about 373 K only: below 373 K the R3 structure purportedly coexists with the I2/m structure.…”

“…2b). Neither the peak shapes nor the FWHM-values show triclinic distortion at below about 200 K [14]. Therefore, the structures of Ba 2 LaIrO 6 at 82rTr 653 K and at TZ663 K can be described in the space groups R3 and Fm3m, respectively.…”

“…The space groups reported thus far for Ba 2 LaIrO 6 are P2 1 /n (at room temperature) [9], R3 (at room temperature or between 373 and 473 K) [11,14], I2/m (at room temperature) [14], I1 (at below about 200 K) [14] and Fm3m (at above about 473 K) [14]. Since neither X-ray [11] nor neutron diffraction data [14] showed superlattice reflections associated with the in-phase tilting, the space group P2 1 /n is ruled out from further consideration.…”

“…Since neither X-ray [11] nor neutron diffraction data [14] showed superlattice reflections associated with the in-phase tilting, the space group P2 1 /n is ruled out from further consideration. Clearly, the remaining space groups contain only out-of-phase tilting (R3, I2/m and I1) or non-tilting ðFm3mÞ resulting in similar superlattice reflections with the Miller indices of odd-odd-odd when indexed with a double cubic cell.…”

“…To see whether the R3-I2=m (via a two phase region of R3 þ I2=m) and the I2=m-I1 phases transitions occur in Ba 2 LaIrO 6 at below about 373 and 200 K, respectively [14], we closely examined the profiles of the basic (222) and (400) reflections as function of temperature (see Fig. 2).…”