Crystal structure of new ternary Th2Ni17-type related compounds in the R-Mn-Al systems (R = Gd, Tb, Dy, Ho, Er)

New hexagonal ternary phases R2-yMnzMnxAl17-x have been obtained in the Mn-rich regions of R-Mn-Al (R = Gd, Tb, Dy, Ho, Er) systems: Gd2-yMnxAl17-x (0≤y≤0.15, 13.0≤x≤15.1); Tb2-yMnxAl17-x (0≤y≤0.23, 13.2≤x≤15.2); Dy2-yMnxAl17-x (0≤y<∼0.2, 11.9≤x≤14.6); Ho2-yMnxAl17-x (0≤y<∼0.2, 11.5≤x≤14.2) and Er2-yMnzMnxAl17-x (0≤y≤0.27, 0≤z≤0.54, 11.3≤x≤14.1). Th2Ni17-type structure occurs in alloys with the content of R = 10.5 at.% (ideal R2X17 stoichiometry). When R < 10.5 at.% two ways of structure constitution are possible: i) formation of the Th2Ni17 - type structure with defective 2(b) atomic position (solid solution of subtraction); ii) formation of the Th2Ni17 - related type structure with the substitution of part of R atoms by the Mn-Mn pairs (solid solution of multiple substitution). (author)