A New Phase with Filled Mg6Cu16Si7 Structure in the Mn–Ni–Ge–Si System: Mechanochemical Synthesis, Crystal and Electronic Structure

Single-phase Mn6Ni16Ge7 and Mn6Ni16Ge7Si samples were obtained using mechanical activation of stoichiometric mixtures in a planetary mill followed by high-temperature annealing at 1000°C in evacuated quartz tubes. The crystal structures of the products were determined from powder diffraction data by the full-profile Rietveld method. Mn6Ni16Ge7 belongs to the Mg6Cu16Si7 structure type (a = 11.41837 (8) Å, Rexp/Rwp/Rp/RBragg, % = 2.05/4.01/2.94/1.991) and Mn6Ni16Ge7Si refers to the U6Fe16Si7C structure type (a = 11.43152(8) Å, Rexp/Rwp/Rp/RBragg, % = 1.92/3.06/2.33/1.542). The differences between the structures are related to the fact that 4b site is occupied by silicon in Mn6Ni16Ge7Si and is vacant in Mn6Ni16Ge7. The melting points and microhardnesses of Mn6Ni16Ge7 and Mn6Ni16Ge7Si were determined. The possibility of the formation of the Mn6Ni16Ge7 and Mn6Ni16Ge7Si phases using spark plasma sintering over a total exposure time of 1 h was demonstrated. Band structure calculations revealed metallic conductivity for both phases and a high degree of mixing of the 3d states of nickel and manganese near the Fermi level. The primary contribution to the chemical bonding is made by interactions involving nickel.