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 14/mmm (No. 139); Pearson's symbol t/10), 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 do 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 T-C 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. (C) 2009 Elsevier Inc. All rights reserved.