Nickel deficiency in RENi2–xP2 (RE=La, Ce, Pr). Combined crystallographic and physical property studies

Large single crystals from RENi2–xP2 (RE=La, Ce, Pr) were synthesized from the pure elements using Sn as a metal flux, and their structures were established by X-ray crystallography. The title compounds were confirmed to crystallize in the body-centered tetragonal ThCr2Si2 structure type (space group I4/mmm (No. 139); Pearsonʹs symbol tI10), but with a significant homogeneity range with respect to the transition metal. Systematic synthetic work, coupled with accurate structure refinements indicated strong correlation between the degree of Ni-deficiency and the reaction conditions. According to the temperature dependent dc magnetization measurements, LaNi2–xP2 (x=0.30(1)), as expected, is Pauli-like paramagnetic in the studied temperature regime, while the Ce-analog CeNi2–xP2 (x=0.28(1)) shows the characteristics of a mixed valent Ce3+/Ce4+ system with a possible Kondo temperature scale on the order of 1000 K. For three different PrNi2–xP2 (x⩽0.5) samples, the temperature and field dependence of the magnetization indicated typical local moment 4f-magnetism and a stable Pr3+ ground state, with subtle variations of TC as a function of the concentration of Ni defects. Field-dependent heat capacity data for CeNi2–xP2 (x=0.28(1)) and PrNi2–xP2 (x=0.53(1)) are discussed as well.