Site occupancy of Ga and Nb in Nd12.5FebalGa0.3Nb0.2B6.2 during the hydrogenation, disproportionation, desorption, and recombination process

The local structure changes around Ga and Nb in Nd12.5FebalGa0.3Nb0.2B6.2 during homogenization, disproportionation, and recombination processes are studied by fluorescence XAFS in order to understand the roles of Ga and Nb on the improvement of (BH)max. Comparing the observed XAFS of the Ga K edge with the calculated ones, Ga is proved to occupy preferentially the Fe(4c) site in Nd2Fe14B structure after homogenization and recombination, while it dissolves in α-Fe after the disproportionation. On the other hand, XAFS results of the Nb K edge does not change in the whole hydrogenation, disproportionation, desorption, and recombination process; the XAFS results of Nb indicate the formation of a stable NbFeB phase in the homogenized state.