Revealing the slow decomposition kinetics of type-I clathrate Ba8Ga16Ge30Electronic supplementary information (ESI) available. See DOI: 10.1039/c7cp01753g

Inconsistencies in high temperature thermoelectric property measurements of Ba 8 Ga 16 Ge 30 have prompted our study on the thermal stability of this heavily studied inorganic clathrate. Using X-ray diffraction, thermal analysis, and imaging techniques on both powder and spark plasma sintered pelletized samples, we probe the structure and decomposition characteristics of this important high temperature thermoelectric material. We demonstrate that the decomposition of Ba 8 Ga 16 Ge 30 is extremely dependent on the heating conditions employed and, as a result of the slow decomposition kinetics of the clathrate, reveal that the true stability of this system has been overlooked in the extensive literature available. Loss of Ga and Ge from the clathrate cage is evident in all high temperature experiments under both air and inert environments. This study serves to highlight that the underlying structural chemistry and stability of thermoelectric materials at high temperature needs to be considered in parallel with the thermoelectric properties which constitute the figure of merit. Only then will reliable thermoelectric modules for real applications be realized. Destabilization of the type I clathrate Ba 8 Ga 16 Ge 30 at moderate temperatures has been revealed, prompting the thermoelectric community to consider the impact of operational temperatures on the stability and reliability of high zT materials.