Strain-Induced Structural Phase Transitions in Epitaxial (001) BiCoO 3 Films: A First-Principles Study.

We have simulated BiCoO 3 films epitaxially grown along (001) direction with density functional theory computations. Leading candidates for the lowest-energy phases have been identified. The tensile strains induce magnetic phase transition in the ground state ( P 4 m m symmetry) from a C-type antiferromagnetic order to a G-type order for the in-plane lattice parameter above 3.922 Å. The G-type antiferromagnetic order will be maintained with larger tensile strains; however, a continuous structural phase transition will occur, combining the ferroelectric and antiferrodistortive modes. In particular, the larger tensile strain allows an isostructural transition, the so-called Cowley's "Type Zero" phase transitions, from C c -(I) to C c -(II), with a slight volume collapse. The orientation of ferroelectric polarization changes from the out-of-plane direction in the P 4 m m to the in-plane direction in the P m c 2 1 state under epitaxial tensile strain; meanwhile, the magnetic ordering temperature T N can be strikingly affected by the variation of misfit strain. [ABSTRACT FROM AUTHOR]