Crystal structure stability, and exsolution process of colusite thermoelectric materials from high temperature in situ synchrotron X-ray pow

Colusites Cu26V2Sn6S32 (VSn) and Cu26Cr2Ge6S32 (CrGe), were recently reported by us as ones of the more promising p-type thermoelectric materials at moderate temperature, with some of the highest figure of merit ZT, 0.93 at 675 K, and 0.86 at 700 K, respectively. We have shown recently from several techniques, that variations of the HT synthesis conditions are able to tune the degree of disorder in VSn colusite, creating by exolution process “composite” materials (ordered and disordered colusite phases) with improved properties. However, by in situ neutron powder diffraction, we also show that HT Induced Disorder approach has limited applicability, related to the crystal structure stability. We propose an in-situ X-ray synchrotron HT powder diffraction study investigating the crystal stability and the exsolution process as a function of the kinetics (temperature variation ramp), and composition on the two p-type colusite (VSn, CrGe) and n-type materials MnBi4S7 and FeBi4S7