Syntheses and crystal structure characterizations of new rare earth nickel bismuth compounds RENiBi2 (RE = La, Pr, Nd and Sm)

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) nm(3); PrNiBi2: a = 0.452714(7) nm, c = 0.95754(4) nm, V = 0.196248(1) nm(3); NdNiBi2: a = 0.452435(2) nm, c = 0.95530(3) nm, V = 0.195516(2) nm(3); SmNiBi2: a = 0.450073(5) nm, c = 0.94292(3) nm, V = 0. 191003(1) nm(3); 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.