Operando structural investigations of thermoelectric materials

Operando characterization provides direct insight into material response under application conditions and it is essential to understand the stability limits of thermoelectric materials and their decomposition mechanisms. An operando setup capable of maintaining a thermal gradient while running DC current through a bar-shaped sample has been developed. Under operating conditions, X-ray scattering data can be measured along the sample to obtain spatially resolved structural knowledge in concert with measurement of electrical resistance and the Seebeck coefficient. Here thermoelectric beta-Zn4Sb3, which is a mixed ionic-electronic conductor, is studied, and a significant temperature dependence of the Zn migration is directly observed. Measurements with the thermal gradient applied either along or opposite to the DC current establish that the ion migration is an electrochemical effect rather than a thermodiffusion. Consideration of only the applied critical voltage or current density is insufficient for deducing the stability limits and structural integrity of materials with temperature-dependent ion mobility. The present operando setup is not limited to studies of thermoelectric materials, and it also lends itself to studies of, for example, ion diffusion in solid-state electrolytes or structural transformations in solid-state reactions.

Automated summary

Operando characterization allows direct insight into material behavior under application conditions, and a new setup has been developed to measure structural, resistance, and Seebeck coefficient data of thermoelectric materials. The temperature-dependent zinc migration in beta-Zn4Sb3 is observed, demonstrating the need to consider electrochemical effects for ion migration properties. The operando setup is versatile beyond thermoelectric materials, making it suitable for studying ion diffusion or structural transformations in solid-state reactions.