Experimental determination of the H-Hf phase diagram using in situ neutron diffraction

The Hf-H(D) system was studied using in situ neutron diffraction as a function of composition (up to 2 D/Hf) and temperature (up to 900 degrees C). This allowed to complement the previous knowledge about this system, in particular from the points of view of the phase existence and of the phase diagram. Two major findings are: the observation of a new phase (gamma, PtS structure type) of composition HfH similar to the monohydride found in H-Zr system, in accordance with previous first-principles calculations, and the structure determination of the 6' phase (new structure type), an ordered superstructure of the 6 phase (CaF2 structure type). Phase relations are established, and a new phase diagram is proposed.(c) 2022 Elsevier B.V. All rights reserved.