New hexagonal ternary phases R2-yMnzMnxAl17-x have been obtained in the Mn-rich regions of the 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 of 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).
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