In Situ Hydrogenation of the Zintl Phase SrGe

Hydrides (deuterides) of the CrB-type Zintl phases AeTt (Ae = alkaline earth; Tt = tetrel) show interesting bonding properties with novel polyanions. In SrGeD4/3-x (gamma phase), three zigzag chains of Ge atoms are condensed and terminated by covalently bound D atoms. A combination of in situ techniques (thermal analysis and synchrotron and neutron powder diffraction) revealed the existence of two further hydride (deuteride) phases with lower H (D) content (called alpha and beta phases). Both are structurally related to the parent Zintl phase SrGe and to the ZrNiH structure type containing variable amounts of H (D) in Sr4 tetrahedra. For alpha-SrGeDy, the highest D content y = 0.29 was found at 575(2) K under 5.0(1) MPa of D-2 pressure, and beta-SrGeDy shows a homogeneity range of 0.47 < y < 0.63. Upon decomposition of SrGeD4/3-x (gamma-SrGeDy), tetrahedral Sr-4 voids stay filled, while the Ge-bound D4 site loses D. When reaching the lower D content limit, SrGeD4/3-x (gamma phase) with 0.10 < x < 0.17, decomposes to the beta phase. All three hydrides (deuterides) of SrGe show variable H (D) content.