Scientific Illustrations -- Perovskite: Pnma vs. Pbnm vs. pseudo-cubic

Bridgmanite is orthorhombic, space group Pbnm, with a = 4.7754 Å, b = 4.9292 Å and c = 6.8969 Å. Sometimes, a pseudo-cubic lattice is introduced with ac ≈ 3.4 Å to compare the slip systems of bridgmanite with those of cubic perovskites. There is a 45° rotation between the Pbnm and the pseudo-cubic indexing, which is a source of great confusion.

Also note that, in some publications bridgmanite is also indexed as Pnma. Axes are swiched between the Pbnm as Pnma indexing. Don't get it wrong!

Perovskite: Pbnm vs. pseudo-cubic

Bridgmanite, viewed down [001] in the Pbnm setting	Bridgmanite with the Pbnm unit cell	Bridgmanite with the pseudo-cubic unit cell	Bridgmanite with the Pbnm and pseudo-cubic unit cells

Perovskite: Pbnm vs. Pnma

Bridgmanite, viewed down [010] in the Pbnm setting	Bridgmanite, viewed down [100] in the Pnma setting	Bridgmanite, viewed down [100] in the Pbnm setting	Bridgmanite, viewed down [001] in the Pnma setting