Hydrogen absorption and desorption in Ta-doped SmFe-based alloys

Abstract

Nitrided Sm 2Fe 17-based materials possess excellent intrinsic magnetic properties, and in this study we have investigated two compositions: Sm 13.8Fe 82.2Ta 4.0 (SmFeTa) and Sm 13.7Fe 86.3 (SmFe). The stoichiometry of all the phases was determined and the SmFeTa material was found to include Ta 3Fe 7 in addition to the Sm 2Fe 17, SmFe 2 and SmFe 3 phases observed in the SmFe alloy, however, it did not exhibit the α-iron dendrites that are characteristic of the binary material. Hydrogen absorption-desorption studies carried out on both materials using thermopiezic and gas-flow analyses demonstrated the different hydrogenation-disproportionation-desorption-recombination (HDDR) behaviour of the SmFeTa alloy. Scanning and transmission electron microscopy studies revealed that in the as-cast structure some 2.0 at.% of Ta is initially dissolved in the Sm 2(FeTa) 17 phase, however, a single HDDR cycle causes the formation of Ta-based precipitates leaving the 2:17 with much less dissolved Ta.