Thermal Stability of High Performance Thermoelectric β‐Zn4Sb3 in Argon

The stability of the high performance thermoelectric β-Zn4Sb3 is investigated by multi-temperature high resolution synchrotron powder X-ray diffraction. Contrary to previous claims β-Zn4Sb3 is not stable when heated in argon and degradation is observed already at 500 K. Nevertheless, the thermal stability of β-Zn4Sb3 is much improved in argon (ca. 5 wt.-% degradation after three heating cycles to 625 K) relative to heating in atmospheric air (ca. 60 wt.-% degradation). Based on identification of the decomposition products two specific degradation processes are proposed, and the excellent stability of β-Zn4Sb3 synthesized by zone melting (equilibrium method) is discussed in relation to the poor stability of material synthesized by thermal quenching (non-equilibrium process). The room temperature peak widths and unit cell parameters change significantly after three heating cycles to 625 K suggesting that the β-Zn4Sb3 phase diagram could be more complex than currently believed.