Hydrides with the perovskite structure: General bonding and stability considerations and the new representative CaNiH3

The stability and electronic structure of perovskite hydrides ABH3 were investigated by means of first-principles density functional calculations. Two types of perovskite hydrides are distinguished: (1) When A and B are alkali and alkaline earth metals, the hydrides are ionic compounds with calculated band gaps of around 2 eV and higher. Their stability trend follows basically the concept of Goldschmidt's tolerance factor. (2) When A is one of the heavier alkaline earth metals (Ca, Sr, Ba) and B a transition metal, stable compounds ABH3 result only when B is from the Fe, Co, or Ni groups. This stability trend is basically determined by effects associated with d band filling of both the transition metal and the hydride. In contrast to group (1) perovskites, the transition metal-containing compounds are metals. The synthesis of CaNiH3 and its structure determination from CaNiD3 is reported. This compound is a type (2) perovskite hydride with a fully occupied hydrogen position (CaNiD3: a=3.551(4) Å, dNi–D=1.776(2) Å). Its stability is discussed with respect to transition metal hydrides with complex anions (e.g., Mg2NiH4, Na2PdH2, Sr2PdH4).

Graphical abstractThe stability and electronic structure of perovskite hydrides ABH3 were investigated by means of first-principles density functional calculations. When A and B are alkali and alkaline earth metals, the hydrides are ionic compounds with calculated band gaps of around 2 eV and higher. When A is one of the heavier alkaline earth metals (Ca, Sr, Ba) and B a transition metal, stable compounds ABH3 result only when B is from the Fe, Co, or Ni groups. In contrast to main group perovskites, the transition metal containing compounds are metals.Figure optionsDownload full-size imageDownload as PowerPoint slide