In-situ investigation of the thermal decomposition of clathrate-I $Ba_{6.2}Si_{46}$

The thermal decomposition behavior of the clathrate-I Ba$_{6.20}$Si$_{46}$ obtained by oxidation of Ba$_4$Li$_2$Si$_6$ with gaseous HCl was investigated in an in-situ synchrotron XRPD experiment. On heating, complex structural rearrangements of the clathrate phase set in. At 600 °C, the formation of silicon is observed. The lattice parameter of the clathrate phase markedly increased along with the Ba occupancy of the dodecahedral cages. Additionally, hints for silicon vacancies in the clathrate framework were found at this temperature. The increase of Ba content on annealing is in remarkable contrast to the behavior previously observed for Ba$_{8−x}$Si$_{46}$ products prepared at high-pressure