Cs2CaH4, a new hydride: The atomic volume of hydrogen as a criterion to check crystal structure and composition

According to the investigations of Park, Pezat, and Darriet CsCaH3 crystallizes in the GdFeO3 structure type. As the resulting atomic volume of hydrogen is too small for a ionic hydride a re-examination of the crystal structure has been carried out. The results of our investigations show that the compound under discussion is actually Cs2CaH4. It crystallizes in the K2NiF4 structure type with the expected atomic volume for hydrogen. The complete crystal structure has successfully been determined by a neutron diffraction experiment on the deuteride Cs2CaD4.