Structure change in Sm–Fe–B–Ti permanent magnet materials induced by HDDR process

The structures of Sm 8.3Fe 85.2B 2.0Ti 4.5 and Sm 9.4Fe 84.1B 2.0Ti 4.5 alloys, which show superior properties as isotropic permanent magnets after a hydrogenation–disproportionation–desorption–recombination (HDDR) process followed by a nitridation, have been investigated by transmission electron microscopy, and electron and X-ray diffraction, paying particular attention to the structural changes induced by the HDDR process. It is found that a hexagonal Th 2Ni 17-type structure, observed in both alloys, with an approximate composition Sm(Fe,Ti) 9.5 before the HDDR process, transforms to a rhombohedral Th 2Zn 17-type structure with a composition Sm(Fe,Ti) 8.5 after the HDDR process. The Ti content in the hexagonal Th 2Ni 17-type structure is higher than that in the rhombohedral structure. The hexagonal Th 2Ni 17-type and rhombohedral Th 2Zn 17-type structures in the Sm 9.4Fe 84.1B 2.0Ti 4.5 alloy have lattice parameters a=0.85103(3) nm and c=0.83820(5) nm, and a=0.85549(3) nm and c=1.24826(9) nm, respectively, and show the relationship a hex < a rhomb but 1/2 c hex>1/3 c rhomb.