Interaction of Samarium with Nickel and Arsenic: Phase Diagram and Structural Chemistry

Solid-state phase equilibria in the Sm-Ni-As system have been established using X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The samarium-poor region up to 33 at. % Sm was studied at 1170 K, whereas the Sm-rich corner, due to the generally lower melting points, was investigated at 770 K. Six ternary compounds were isolated, among which two have been structurally characterized. The hexagonal structure of SmNiAs (SrPtSb-type) was solved from X-ray single crystal data: space group 6̅m2, a = 4.0904(3), c = 3.8957(4) Å , Z = 1, R1 = 0.0221, wR2 = 0.0224 for 134 unique reflections with I_o > 2σ (I_o) and 9 variable parameters. The crystal structure of Sm₆Ni₁₅As₁₀ (Tb₆Ni₁₅As₁₀-type) was determined from X-ray powder diffraction data: full profile refinement, space group P6₃/m, a = 17.0632(4), c = 3.9526(1) Å , Z = 2, RB = 0.079, R_p = 0.138