Electronic structure ofBiMO3multiferroics and related oxides

Abstract

We have performed a systematic study of the electronic structures of the BiMO 3 ͑M =Sc,Cr,Mn,Fe,Co,Ni͒ series by soft x-ray emission ͑XES͒ and x-ray absorption ͑XAS͒ spectroscopy. The band gaps were estimated for all compounds in the series. For BiFeO 3 , a band gap of ϳ0.9 eV was obtained from the alignment of the O K␣ XES and O 1s XAS. The O 1s XAS spectrum of BiNiO 3 indicates that the formation of holes was due to a Ni 2+ valency rather than a Ni 3+ valency. We have found that the O K␣ XES and O 1s XAS, probing partially occupied and vacant O 2p states, respectively, are in agreement with the O 2p densities of states obtained from spin-polarized band-structure calculations for all BiMO 3 compounds addressed herein. The O K␣ XES spectra show the same degree of Bi 6s-O 2p hybridization for all compounds in the series. We speculate herein that the stereochemical activity of the Bi 6s lone pairs must be supplemented with inversion symmetry breaking to allow electric polarization. For BiMnO 3 and BiFeO 3 , two cases of multiferroic materials in this series, the former breaks the inversion symmetry due to the antiferromagnetic order induced by particular orbital ordering in the highly distorted perovskite structure and the latter has rhombohedral crystal structure without inversion symmetry.

BiVO3 : A Bi-based material with promising uv-visible light absorption properties

“…A direct bandgap value of 1.96 eV is calculated at the point (center of the BZ) and this value indeed falls in the visible region of the spectra. Such a calculated low band-gap value is in line with the general trend from the Bi-based transition metal perovskite family, e.g., BiCrO 3 (1.5 eV) [27], BiMnO 3 (1.1 eV) [28], BiFeO 3 (2.5 eV) [29].…”

“…Among the first row transition metals, Bi-based perovskites with Sc, Cr, Fe, Mn, Co, and Ni at the B site have already been realized. Among them, BiFeO 3 and BiMnO 3 have been extensively investigated and they are demonstrated to be multiferroic [27,32,37]. Early attempts to synthesize BiVO 3 [38,39] and BiTiO 3 [38] have not been successful due to the oxidation of V 3+ and Ti 3+ to their 4+ oxidation state, which resulted in the formation of Bi 4 M 3 O 12 (M = V,Ti) [38,40].…”

“…Several perovskites have shown stable photocatalytic activity under illumination, e.g., SrTiO 3 [21], NaTaO 3 [22], KTaO 3 [22], AgTaO 3 [23]. Many Bi-based (especially with transition metals) low band-gap semiconductors have also been realized, e.g., BiVO 4 (2.4 eV) [24], BiInO 3 (2.08 eV) [25], BiGaO 3 (2.03 eV) [26], BiCrO 3 (1.5 eV) [27], BiMnO 3 (1.1 eV) [28], BiFeO 3 (2.5 eV) [29]. In addition to the observed catalytic activity, Bi-based (Bi 3+ ) oxide perovskites have recently gained much interest due to their multifunctionality [30,31].…”

Structural and Electronic Properties of Bixo<sub>3</sub> (X = Mn, Fe, Cr)

“…Note that a large part of the moment is delocalized into magnetic atom. The magnetic moment of 2.3 μB (for Cr atoms) was obtained in spin-polarized calculation in good agreement with the value 2.55 μB obtained in neutron diffraction experiments [48] and even by the LMTO method are found 2.63 μB [49]. The calculated magnetic moment for Mn ions is 2.42 μB which is smaller than the experimen-tal and theoretical values shown in Table 2.…”

Orthorhombic Phase of La0.5Bi0.5NiO3 Studied by First Principles

“…Variation of valence states can lead to notable phenomena such as superconductivity, magnetoresistance, negative thermal expansion in transition metal oxides. Much efforts has been focused on BiNiO 3 proved to undergo a phase transition accompanied by the charge redistribution between Bi and Ni ions [3,4,6,7]. In ambient conditions, BiNiO 3 in triclinic structure (P-1) displays the antiferromagnetic insulating ground state (G-type AFM, T N =300 K) [8], as well as exhibits an unusual charge distribution of Bi .…”