In-situ investigation of the thermal decomposition of clathrate-I Ba6.2Si46

The thermal decomposition behavior of the clathrate-I Ba6.20Si46 obtained by oxidation of Ba4Li2Si6 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 Ba8−xSi46 products prepared at high-pressure.

► Above 550 °C the clathrate-I Ba6.20Si46 undergoes complex structural rearrangements.
► Ba occupancy of the dodecahedral cages rises, while elemental Si is segregated from the phase.
► Intensity distribution in the diffraction patterns points to vacancies in the Si-framework.
► The gain in Ba content on annealing contrasts the behavior of Ba8−xSi46 high-pressure products.