Using first-principles calculations, we study theoretically the stable $2H$ hexagonal structure of BaMnO${}_3$. We show that from the stable high-temperature $P{6}_3/mmc$ structure, the compound should exhibit an improper ferroelectric structural phase transition to a $P{6}_{3}cm$ ground state. Combined with its antiferromagnetic properties, $2H$-BaMnO${}_3$ is therefore expected to be multiferroic at low temperature. The phase transition mechanism in ${\mathrm{BaMnO}}_3$ appears similar to what was reported in YMnO${}_3$ in spite of totally different atomic arrangement, cation sizes, and Mn valence state.

• Received 8 February 2013

DOI:https://doi.org/10.1103/PhysRevB.87.140403