Demchenko G. Synthesis and crystal structure of the compounds in the Er-{Fe,Co,Ni}-Al-Ge systems

The phase composition of alloys in the Er-{Fe,Co,Ni}-Al-Ge systems at 25.0, 33.3, 40.0 at. % Er cross-sections of the isothermal tetrahedron (T = 600 °C) was determined. 10 new quaternary compounds (2 in Er-Fe-Al-Ge, 2 in Er-Co-Al-Ge and 4 in Er-Ni-Al-Ge) and 5 quaternary solid solutions in these and related systems were synthesized and their crystal structures were determined by X-ray diffraction methods. The compound Er5Ni3Al3Ge4 represents a new structure type of inorganic compounds. The number of compounds decreases with increasing number of components and the probability of formation of a new "original" structure type of inorganic compounds decreases too. Crystal structures of quaternary compounds are ordered variants of the binary and ternary types or intergrowth of their structure fragments. A comparison of the investigated systems with related systems was performed and it is stated that for the Er-M-Al-Ge (M = Fe, Co or Ni) systems tendency for the formation of quaternary compounds with ordered structures is observed for the values rM/Al/Ge/rR > 0.77, whereas solid solutions based on ternary compounds form for the values rM/Al/Ge/rR < 0.77.