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 (γ 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 α and β
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 α-SrGeDy, the highest D content y = 0.29 was found
at 575(2) K under 5.0(1) MPa of D2 pressure, and β-SrGeDy shows a homogeneity range of 0.47 < y < 0.63. Upon decomposition of SrGeD4/3–x (γ-SrGeDy), tetrahedral
Sr4 voids stay filled, while the Ge-bound D4 site loses
D. When reaching the lower D content limit, SrGeD4/3–x (γ phase) with 0.10 < x < 0.17, decomposes to the β phase. All three hydrides (deuterides)
of SrGe show variable H (D) content.