This PhD thesis presents investigations of hydrogen incorporation in Zintl phases and transition metal oxides. Hydrogenous Zintl phases can serve as important model systems for fundamental studies of hydrogen-metal interactions, while at the same time hydrogen-induced chemical structure and physical property changes provide exciting prospects for materials science. Hydrogen incorporation in transition metal oxides leads to oxyhydride systems in which O and H together form an anionic substructure. The H species in transition metal oxides may be highly mobile, making these materials interesting precursors toward other mixed anion systems. 

Zintl phases consist of an active metal, M (alkali, alkaline earth or rare earth) and a more electronegative p-block metal or semimetal component, E (Al, Ga, Si, Ge, etc.). When Zintl phases react with hydrogen, they can either form polyanionic hydrides or interstitial hydrides, undergo full hydrogenations to complex hydrides, or oxidative decomposition to more E-rich Zintl phases. The Zintl phases investigated here comprised the CaSi₂, Eu₃Si₄, ASi (A= K, Rb) and GdGa systems which were hydrogenated at various temperature, H₂ pressure, and dwelling time conditions. For CaSi₂, a regular phase transition from the conventional 6R to the rare 3R took place and no hydride formation was observed. In contrast, GdGa and Eu₃Si₄ were very susceptible to hydrogen uptake. Already at temperatures below 100 ºC the formation of hydrides GdGaH_2-x and Eu₃Si₄H_2+x was observed. The magnetic properties of the hydrides (antiferromagnetic) differ radically from that of the Zintl phase precursor (ferromagnetic). Upon hydrogenating ASi at temperatures around 100 ^oC, silanides ASiH₃ formed which contain discrete complex ion units SiH₃^-. The much complicated β – α order-disorder phase transition in ASiH₃ was evaluated with neutron powder diffraction (NPD), ²H NMR and heat capacity measurements. 

A systematic study of the hydride reduction of BaTiO₃ leading to perovskite oxyhydrides BaTiO_3-xH_x was done. A broad range of reducing agents including NaH, MgH₂, CaH₂, LiAlH₄ and NaBH₄ was employed and temperature and dwelling conditions for hydride reduction examined. Samples were characterized by X-ray powder diffraction (XRPD), thermal gravimetric analysis and ¹H NMR. The concentration of H that can be incorporated in BaTiO_3-xH_x was found to be very low, which is in contrast with earlier reports. Instead hydride reduction leads to a high concentration of O vacancies in the reduced BaTiO₃. The highly O-deficient, disordered, phases - BaTiO_3-xH_y□_(x-y) with x up to 0.6 and y in a range 0.05 – 0.2 and (x-y) > y – are cubic and may represent interesting materials with respect to electron and ion transport as well as catalysis.