High-pressure synthesis and physical properties of the BaIrO$_{3}$ polytypes

The ambient 9R-BaIrO$_{3}$ exhibits a ferromagnetic transition at T$_{c}\approx $ 180 K followed by a charge density wave at nearly the same temperature.\footnote{G. Cao\textit{, et al}., Solid State Comm. \textbf{113}, 657 (2000).} By using the 9R phase as the staring material, we were able to synthesize a series of the polytypes of BaIrO$_{3,} \quad i.e.$ 5H, 6H and 3C phases under high pressure up to 10 GPa at 1000\r{ } C.\footnote{J.-G. Cheng, \textit{et al}, J. Am. Chem. Soc. \textbf{131}, 7461 (2009).} These high-pressure phases are quenchable to ambient pressure. The 5H phase has the stacking sequence \textit{hchcc} that is a new member in the hexagonal polytypes of AMO$_{3}$ perovskites. With increasing fraction of the corner- to face-sharing IrO$_{6/2}$ octahedra in the sequence 9R$\to $5H$\to $6H, the ground states of BaIrO$_{3}$ evolve from a ferromagnetic insulator with T$_{c }\approx $ 180 K in the 9R phase to a ferromagnetic metal with T$_{c} \approx $ 50 K in the 5H phase, and finally to an exchange-enhanced paramagnetic metal near a quantum critical point in the 6H phase.\footnote{J.-G. Cheng, \textit{et al}., Phys. Rev. B \textbf{80}, 104430 (2009).}