Neutron Powder Diffraction Study on the Crystal and Magnetic Structures of BiCrO₃

Abstract

The crystal and magnetic structures of polycrystalline BiCrO3 were determined by the Rietveld method from neutron diffraction data measured at temperatures from 7 to 490 K. BiCrO3 crystallizes in the orthorhombic system above 420 K (space group Pnma; Z = 4; a = 5.54568(12) Å, b = 7.7577(2) Å, and c = 5.42862(12) Å at 490 K) in the GdFeO3-type structure. Below 420 K down to 7 K, a monoclinic structure is stable with C2/c symmetry (a = 9.4641(4) Å, b = 5.4790(2) Å, c = 9.5850(4) Å, and β = 108.568(3)° at 7 K). A possible model for antiferromagnetic order below T N = 109 K is proposed with a propagation vector of k = (0, 0, 0). In this model, magnetic moments of Cr3+ ions are coupled antiferromagnetically in all directions, forming a G-type antiferromagnetic structure. Refined magnetic moments at 7, 50, and 80 K are 2.55(2)μB, 2.43(2)μB, and 2.09(2)μB, respectively. The structure refinements revealed no deviation from stoichiometry in BiCrO3.

Strain dependent microstructural modifications of BiCrO3 epitaxial thin films

“…The crystallographic phase content of the tensile strained BCOSTO films was found to be an orthorhombic structure, whereas the BCONGO films exhibit a monoclinic symmetry. Thus, in contrast to the previous reports on multiple phase coexistence within the BCO bulk [17][18][19][20] or thin films [21], the present work suggests a variation in crystal structure, depending on whether the BCO films experienced tensile (BCOSTO) or compressive (BCONGO) inplane strain. The tensile-strained orthorhombic BCOSTO films of thicknesses, d ≳ 50 nm exhibit a high density of edge-type dislocations originating near the BCO/SRO interface, which could be attributed to the semicoherent growth and an epitaxial strain relaxation.…”

“…Belik et al [17] have reported that bulk BCO ceramics exhibit a monoclinic (C2/c) crystal symmetry at RT, which transforms into an orthorhombic symmetry (Pnma) at around 420 K . However, later, the same authors [18] noted that the monoclinic BCO phase retains about 10 to 15 volume percentage of an orthorhombic phase, suggesting multiple phase coexistence in BCO, (ii) Goujon et.…”

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.…”

Density functional study of weak ferromagnetism in a thick BiCrO3 film

“…There is a structural phase transition at about 430 K, above which it agreed [5][6][7][8] that BCO crystallizes in an orthorhombic structure with the Pnma space group (no.62). Below 430 K x-ray powder diffraction patterns (XPD) were interpreted 6 to yield a C2(space group no.5) monoclinic structure.…”