Single crystals with this composition were found to grow in the SrO-IrO2 system. A single-crystal structure determination indicated a tetragonal structure (I4/mmm, a = 0.3890, c = 1.6890nm), and revealed an alternating stacking of single and double IrO6 perovskite layers which were interleaved with SrO layers along the c-axis. It was found that, although the refined metal-O distances were reasonable, the thermal parameters of one heavy atom (Ir) and one light atom (O) were non-positive definite. A careful examination of Weissenberg and transmission electron micrographs showed that the single crystals contained random distributions of single and double IrO6 perovskite layers which arose from the inter-growth of Sr2IrO4 and Sr3Ir2O7 phases. This work highlighted the dangers of relying on diffractometry data alone for structural analysis.

R.L.Harlow, Z.G.Li, W.J.Marshall, M.K.Crawford, M.A.Subramanian: Materials Research Bulletin, 1995, 30[2], 217-23