(Color online) The 2 × 2 × 2 BiCoO3 superlattice with the bismuth (purple), cobalt (blue), and two nonequivalent oxygen atoms (red), marked as Bi, Co, O1, and O2.
The polarization value (a), c/a (b), and volumes (c) of pure BiCoO3 under epitaxial strains from 0 to 5%.
GGA + U calculated stable chemical potential region (ABCD) for BiCoO3.
(Color online) Formation energy of O vacancy with respect to the Fermi energy for (a) without strain condition and (b) 2% strain condition. The O chemical potential regions are varied within oxygen poor condition (ΔμO = –1.319 eV, lower lines/red) to oxygen rich condition (ΔμO = 0, upper lines/black). Only the formation energies of the stable charge state of O vacancy at corresponding Fermi level are shown. The Fermi level shifts from VBM, set to zero here, to the CBM of BiCoO3 with corresponding strain.
Spin charge density of BiCoO3 on (010) planes across the vacancy of (a) , (b) , and (c) , respectively. The spins up and down densities are denoted by solid and dashed lines, respectively. Here, the spin density contours start at 0.001 e/Å3 and increases successively by a factor of .
(Color online) Total density of states (TDOS) of (a) pure BiCoO3, (b) , (c) , and (d) .
(Color online) The decomposed DOS of Co 3d levels in ideal BiCoO3 [(a), (b)], nearby [(c), (d)], and [(e), (f)]. The occupation of the decomposed levels is also illustrated in the right side of the DOS. Here, the VBM is set to 0 and the spins up and down plots are denoted by positive and negative values, respectively.
The Born effective charges (BEC) of Bi, Co, and O under various tensile strains.
The calculated polarization value along the 〈001〉 direction for pure BiCoO3 and those with various O vacancies under situations of no strain and 2% strain.
The relative atomic displacement along the 〈001〉 direction with respect to their ideal lattice sites in BiCoO3 at no strain and 2% strain for Bi, Co, O1, and O2 near the vacancies. Positive and negative values stand for shifting up and down, respectively (c.f. Fig. 1 ).
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