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

Chem. Met. Alloys 2 (2009) 157-163

https://doi.org/10.30970/cma2.0113

Roksolana KOZAK, Yaroslav TOKAYCHUK, Mykola MANYAKO, Roman GLADYSHEVSKII

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 germanides, CeAg_0.8Ge_1.2-CeAl_1.6-1.5Ge_0.4-0.5, PrAg_0.8Ge_1.2-PrAl_1.55-1.48Ge_0.45-0.52, and NdAg_0.7Ge_1.3-NdAl_1.63-1.50Ge_0.37-0.50, and a quaternary compound, SmAg_0.55-0.36Al_0.43-0.80Ge_1.02-0.84, with AlB₂-type structure (Pearson symbol hP3, space group P6/mmm). The crystal structure of the solid solution in the system Pr-Ag-Al-Ge was refined for the composition PrAg_0.38Al_0.80Ge_0.82 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-size 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.

Unit-cell parameters vs. valence electron concentration within the homogeneity ranges of the AlB₂-type compounds in the quaternary systems {Ce,Pr,Nd,Sm}-Ag-Al-Ge.

Keywords

Rare-earth / Silver / Aluminum / Germanium / Solid solution / X-ray diffraction / Crystal structure