Neutron powder diffraction study on the crystal and magnetic structures of BiCrO3

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) angstrom, b = 7.7577(2) angstrom, and c = 5.42862(12) angstrom 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) angstrom, b = 5.4790(2) angstrom, c = 9.5850(4) angstrom, and P = 108.568(3)degrees 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)mu(B), 2.43(2)mu(B), and 2.09(2)mu(B), respectively. The structure refinements revealed no deviation from stoichiometry in BiCrO3.