Syntheses and Crystal Structure Characterizations of New Rare Earth Nickel Bismuth Compounds RENiBi_2 (RE=La, Pr, Nd and Sm)

摘要

The title new compounds with chemical formula RNiBi2 were synthesized by arc melting method followed by annealing. The crystal structures refined using Rietveld method and X-ray powder diffraction data show to be isotypic to CaMnBi2 structure type with space group P4/nmm （No.129）. The unit cell parameters are LaNiBi2: a=0.454238（2） nm, c=0.96845（3） nm, V=0.199822（3） nm3; PrNiBi2: a=0.452714（7） nm, c=0.95754（4） nm, V=0.196248（1） nm3; NdNiBi2: a=0.452435（2） nm, c=0.95530（3） nm, V=0.195516（2） nm3; SmNiBi2: a=0.450073（5） nm, c=0.94292（3） nm, V=0.191003（1） nm3; respectively, showing lanthanide contraction. The structure was characterized by layers of edge-shearing NiBi4 tetrahedron and covalently bonded Bi square net separated by rare earth atoms.