Mapping formation conditions and phase relations of hydrogen-rich phases in the ternary systems A-Si-H (A = Na, Li)

Recently it has been shown that hydrogenation reactions at 4 - 10 GPa afford unique all-hydrido hypervalent [SiH6]2- complexes in the crystalline hydridosilicates A2SiH6 (A = K, Rb). This suggests that a broader diversity of anionic hypervalent silicon hydride species should be attainable. Their bonding properties closely relate to those of the recently discovered superconducting phases PH2 and H3S. The latter shows a record high Tc of 203 K. However, these binary phases can only be observed at ultrahigh pressures >100 GPa. At the same time, switching to ternary systems can lower the synthesis pressures down to several GPa. We propose to perform in situ studies of reactions AH+Si+H2 (A = Li, Na) at pressures around 9 GPa and in a temperature range 300 – 700 °C, using ID06-LVP, ESRF. The aim is to exploit the well-controlled p,T environment in LVP experiments to unfold formation conditions and phase relations of new ternary A-Si-H hydrides containing novel hypervalent Si-H species.