Solid solutions with AlB2-type structure in R-Ag-Al-Ge systems (R = Ce, Pr, Nd, Sm)

An investigation of the quaternary systems R–Ag–Al–Ge (R = Ce, Pr, Nd, Sm) at 873 K led to the discovery of three complete solid solutions based on ternary ger manides, CeAg0.8Ge1.2-CeAl1.6-1.5Ge0.4-0.5, PrAg0.8Ge1.2PrAl 1.55-1.48Ge0.45-0.52, and NdAg0.7Ge1.3-NdAl 1.63-1.50Ge0.37-0.50, and a quaternary compound, SmAg0.55-0.36Al 0.43-0.80Ge1.02-0.84, with AlB 2-type structure (Pearson symbol hP3, space group P6/mmm). The crystal structure of the solid solution in the syst em Pr-Ag-Al-Ge was refined for the composition PrAg0.38Al 0.80Ge0.82 from X-ray powder (a = 0.43368(5), c = 0.41929(7) nm) and single-crystal ( a = 0.4318(1), c = 0.4191(1) nm) diffraction data. Within the homogeneity range the contact distances between small-si ze atoms decrease with increasing Al and decreasing Ag and Ge content. The valence electron concentration per atom of the statistical mixture Ag+Al+Ge increases from 4.30 to 4.76 within the same range.