Polygermanosilyne Calcium Hydroxide Intercalation Compounds Formed by Topotactic Transformation of Ca(Si 1 − x Ge x )2 Alloy Zintl Phases in Ambient Atmosphere

Epitaxial thin films of Ca(Si 1 − x Ge x )2 with 0 < x ≤ 1 are found to react with the moisture of ambient atmosphere to form new Ca-Si-Ge-O-H compounds which were studied by X-ray diffraction, energy dispersive X-ray analysis, infrared absorption, and thermally induced hydrogen desorption measurements. Pure CaGe2 forms the polygermyne calcium hydroxide intercalation compound Ca(OH)2(GeH)2 upon exposure to humidity, with a trigonal tr6 crystal lattice with a = 4.00(1) and c = 65.3(1)A. In mixed Ca(Si 1 − x Ge x )2 with smaller Ge content, the group-14 layers are subject to intense oxidation leading to decreased crystallinity. The products exhibit characteristic colours and intense photoluminescence, the peak luminescence varying from 1.35 eV for the reaction product of Ca(Si0.3Ge0.7)2 to 2.6 eV for that of Ca(Si0.5Ge0.5)2.