Phase equilibria and crystal structures of the compounds in the Pr-Ni-Sb system at 870Â K

The isothermal section of the Pr-Ni-Sb system at 870 K over the whole concentration region has been built using X-ray analysis. At the temperature of the investigation three already known ternary antimonides PrNiSb, ∼PrNiSb2 and ∼PrNi2Sb2 have been confirmed and three compounds ∼Pr5NiSb2, PrNiSb3, and PrNi2+xSb2−y have been synthesized for the first time. The crystal structures of the obtained compounds belong to the following structure types: PrNiSb-ZrBeSi type, space group P63/mmc, a = 0.43838(2) nm, c = 0.81068(6) nm; PrNiSb3-CeNiSb3 type, space group Pbcm, a = 1.2579(2) nm, b = 0.62051(8) nm, c = 1.8371(2) nm; ∼Pr5NiSb2-structure related to Y5NixSb3−x-type, space group Pnma, a = 1.2457(1) nm, b = 0.9159(1) nm, c = 0.8118(1) nm. The PrNi2Sb2 compound crystallizes with an orthorhombic or monoclinic unit cell and a structure related to the tetragonal CaBe2Ge2 type. The PrNi2+xSb2−y antimonide has a small homogeneity region and crystallizes with a tetragonal unit cell (space group P4/nmm) and lattice parameters a = 0.431256(9) − 0.4319(1) nm, c = 0.99830(2) − 1.0092(3) nm. The existence of a considerable homogeneity region of the PrNi0.62−1.35Sb2 compound is caused by a deficiency of Ni atoms or their excess compared to the initial structure of stoichiometric composition and a corresponding transition from the HfCuSi2 type to the CaBe2Ge2 type with preservation of the unit cell symmetry (a = 0.43539(4) − 0.44130(2) nm, c = 0.9653(1) − 0.97643(5) nm).