High-pressure BaCrO3 polytypes and the 5H–BaCrO2.8 phase

Polytypism of BaCrO3 perovskites has been investigated at 900–1100 °C and pressures up to 22 GPa. Hexagonal 5H, 4H, and 6H perovskites are observed with increasing pressure, and the cubic 3C perovskite (a=3.99503(1) Å) is observed in bulk form for the first time at 19–22 GPa. An oxygen-deficient material with limiting composition 5H–BaCrO2.8 is synthesised at 1200 °C under ambient pressure. This contains double tetrahedral Cr4+ layers and orders antiferromagnetically below 260 K with a (0 0 1/2) magnetic structure.

Graphical abstractHexagonal 5H, 4H, and 6H perovskites polytypes of BaCrO3 are observed with increasing pressure and the cubic 3C perovskite is stabilised in bulk form for the first time at 19–22 GPa. Oxygen-deficient 5H–BaCrO2.8 synthesised at ambient pressure contains double tetrahedral Cr4+ layers and orders antiferromagnetically below 260 K with a (0 0 1/2) magnetic structure.Figure optionsDownload full-size imageDownload as PowerPoint slide