Abstract
To clarify the mechanism of negative thermal expansion in perovskite BiNiO3, the structural, magnetic, and electronic properties of BiNiO3 in high-temperature orthorhombic and low-temperature triclinic phases are investigated within first-principles calculations. The optimized structures are ferromagnetic (FM) with 1.732μB/Ni adopting orthorhombic configuration and G-type antiferromagnetic (G-AFM) in triclinic phase. The electronic density of states (DOSs) and calculations of band valence sums (BVSs) show that the oxidation states are high-spin 3d7:t2g5eg2 of nickel in orthorhombic with Bi3+Ni3+O3, and an intermetallic charge transfer between Ni and Bi ions leading to Bi3+0.5Bi5+0.5Ni2+O3 of triclinic phase. Shrinkage about ∼1.07% in cell volume is attributed to the release of stress induced by changes of Ni–O and Bi–O bonds, which are corresponding to the changes of oxidation states in Bi and Ni ions.
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