Theoretical Design of Yttrium Oxyhydrides: Remarkable Richness of Phase Diagram

The synthesis of stable yttrium oxyhydride-type compounds raised a question regarding the key factors that may be responsible for formation routes and structural features of these attractive materials. For solving this problem the interplay of chemical composition and crystalline architectures has been theoretically explored in terms of possible structural transformations caused by the gradual oxidation of the host metal-hydride system. The combination of group-theory methods, mixed-anion chemistry arguments, and relevant DFT calculations provided us with the opportunity to predict and characterize the candidate models for most probable stoichiometric versions of yttrium oxyhydrides. The predicted chemical compositions along with the crystallization results have been summarized in the phase diagram. It is shown that structural stability is achieved by matching favorable crystallographic positions of the nearest oxygen and hydrogen atoms at the metal center.