Strain-Induced Structural Phase Transitions in Epitaxial (001) BiCoO3 Films: A First-Principles Study

Abstract

We have simulated BiCoO3 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 (P4mm 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 Cc-(I) to Cc-(II), with a slight volume collapse. The orientation of ferroelectric polarization changes from the out-of-plane direction in the P4mm to the in-plane direction in the Pmc21 state under epitaxial tensile strain; meanwhile, the magnetic ordering temperature TN can be strikingly affected by the variation of misfit strain.

First‐Principles Investigations of the Structural Phases of Low‐Spin State of BiCoO3

“…This suggests that the polar phase could be further stabilized experimentally through, e.g., strain engineering techniques. [40,41] However, it is important to note that, despite the larger ionic radii of HS Co 3þ (0.75 Å) compared to LS Co 3þ (0.69 Å), both the LS and HS states of BiCoO 3 are expected to exhibit a tendency toward a nonpolar antiferrodistortive phase due to their tolerance factors being lower than 1. [32] Comparing the LS and HS phases in Figure 4 reveals significantly larger energy gains for the HS case.…”