Novel type of ferroelectricity in brownmillerite structures: A first-principles study

Authors

H. Tian, X.Y. Kuang, A.J. Mao, Y.R. Yang, H.J. Xiang, C.S. Xu, S.O. Sayedaghaee, J. Iniguez, and L. Bellaiche 

Reference

Physical Review Materials, vol. 2, no. 8, art. no. 084402, 2018 

Description

First-principles calculations are conducted on two magnetic brownmillerites, namely, Ca₂Co₂O₅ and Sr₂Co₂O₅. Both systems possess a previously overlooked polar Pmc2₁ phase that is low in energy. This ferroelectric state is even predicted to be the ground state of Sr₂Co₂O₅, which therefore renders such material multiferroic. Strikingly, the ferroelectricity associated with this Pmc2₁ phase involves an original energetic coupling that is linear in the polar mode, quadratic in another distortion, and linear in a third mode. Such ferroelectricity is therefore of a novel type, since it differs from previously reported proper, improper, hybrid improper, and triggered kinds of ferroelectricity.

Link

doi:10.1103/PhysRevMaterials.2.084402