X-ray scattering study of thermoelectric β-ZnSb.

The application of thermoelectrics for energy harvesting depends strongly on operational reliability and it is therefore desirable to investigate the structural integrity of materials under operating conditions. We have developed an setup capable of simultaneously measuring X-ray scattering data and electrical resistance on pellets subjected to electrical current. Here, investigations of β-ZnSb are reported at current densities of 0.5, 1.14 and 2.3 A mm. At 0.5 A mm no sample decomposition is observed, but Rietveld refinements reveal increased zinc occupancy from the anode to the cathode demonstrating zinc migration under applied current. At 1.14 A mm β-ZnSb decomposes into ZnSb, but pair distribution function analysis shows that ZnSb units are preserved during the decomposition. This identifies the mobile zinc in β-ZnSb as the linkers between the ZnSb units. At 2.3 A mm severe Joule heating triggers transition into the γ-ZnSb phase, which eventually decomposes into ZnSb, demonstrating Zn ion mobility also in γ-ZnSb under electrical current.