The ternary RE–Si–B systems (RE = Dy, Ho, Er and Y) at 1270 K: Solid state phase equilibria and magnetic properties of the solid solution REB 2− xSi x (RE = Dy and Ho)

Abstract

The solid state phase equilibria in the ternary RE–Si–B diagrams (RE = Dy, Ho, Er and Y) were determined at 1270 K using experimental techniques such as X-ray diffraction, scanning electron microscopy and electron probe microanalysis. In general, three ternary phases were obtained for each diagram: the line compound RE 5Si 2B 8 with tetragonal symmetry, the boron-inserted Nowotny phase RE 5Si 3B x of Mn 5Si 3-type and the solid solution REB 2− x Si x of AlB 2-type. Prior to this work, the binary systems RE–Si and RE–B, which form the boundary of each diagram, were also re-investigated. In addition to the structures of RE 5Si 3 (Mn 5Si 3-type, RE = Dy, Ho and Y) and Dy 3Si 4 (Ho 3Si 4-type) which were previously reported or will be presented in a forthcoming paper, the X-ray single crystal structures of RE 5Si 4 (Sm 5Ge 4-type, RE = Dy and Ho), DySi (CrB-type) and HoSi in both polymorphic modifications, i.e. the FeB- (high temperature) and CrB- (low temperature) types, were determined and are described herein. Structural relationships between members of the same series on one side, and between both forms of HoSi on the other side, are also discussed in terms of coordination polyhedra and interatomic distances. Finally, magnetic measurements were performed on the alloys REB 2− x Si x , which in case of RE = Dy exhibit a marked increase of the magneto-crystalline anisotropy, whereas for RE = Ho a change from ferromagnetic to antiferromagnetic behaviour with increasing silicon content is encountered.