In Operando Study of High‐Performance Thermoelectric Materials for Power Generation: A Case Study of β‐Zn₄sb₃

Abstract

To date, many high-performance thermoelectric (TE) materials for power generation have been studied and reported. However, so far they have not been implemented in reliable commercial devices. To bring current achievements into a device for power generation, a full understanding the dynamic behavior of thermoelectric materials under operating conditions is needed. In this work, an in operando study is conducted on the high-performance TE material β-Zn4Sb3 under large temperature gradient and thermal cycling by a new approach using in-situ transmission electron microscopy combined with characterization of the TE properties. We found that after 30 thermal cycles in a low-pressure helium atmosphere the TE performance of β-Zn4Sb3 is maintained with the zT value of 1.4 at 718 K. Nevertheless, under a temperature gradient of 380 K (Thot = 673 K and Tcold = 293 K) operating for only 30 hours, zinc whiskers gradually precipitate on the cold side of the β-Zn4Sb3 leg. The dynamical evolution of Zn in the matrix of β-Zn4Sb3 was found to be the source that leads to a high zT value by lowering of the thermal conductivity and electrical resistivity, but it is also the failure mechanism for the leg under these conditions. The in operando study brings deep insight into the dynamic behavior of Advanced Electronic Materials 2 nanostructured TE materials for tailoring future TE materials and devices with higher efficiency and longer durability.

Enhanced thermoelectric performance and high-temperature thermal stability of p-type Ag-doped β-Zn4Sb3

“…The weak diffraction peak of ZnSb appears when the sample was cooled to 301 K in the second cycle, but it disappears as the temperature increases to 793 K in the third cycle, which can be seen more clearly from Figure 6 In order to investigate the thermal stability of the bulk samples in air, undoped Zn 4 Sb 3 and (Zn 0.9925 Ag 0.0075 ) 4 Sb 3 samples were both characterized by insitu XRD measurements. The results shown in Figure 7 reveal that there are Zn whiskers coming out of the surface on the two edges for the undoped Zn 4 Sb 3 bulk sample, which is in agreement with the observation reported by Hung et al [45]. However, no Zn whisker is observed for the (Zn 0.9925 Ag 0.0075 ) 4 Sb 3 bulk sample.…”

Operando structural investigations of thermoelectric materials

“…This structural complexity is believed to be the main origin of the low thermal conductivity found in this system, which is highly desirable for thermoelectric applications (Nylé n et al, 2004;Cargnoni et al, 2004;Snyder et al, 2004). When placed in a potential gradient, the Zn ions have been shown to migrate along the current direction, which ultimately results in an irreversible decomposition of -Zn 4 Sb 3 into ZnSb in the Zn-deficient region, and elemental Zn is observed in the Zn-rich region of the sample (Yin et al, 2012(Yin et al, , 2014Jørgensen et al, 2020;Hung et al, 2017). It was generally assumed that the migrating Zn ions were positioned on the interstitial sites, but pair distribution func-tion and powder X-ray diffraction (PXRD) data measured using our initial operando setup suggested Zn atoms on the main lattice site, Zn1, as the migrating species (Jørgensen et al, 2020).…”

Operando X-ray scattering study of thermoelectric β-Zn4Sb3

“…Apart from the obvious need for high performance, low cost and environmentally friendly materials, one of the main obstacles of TE technology is the lack of material stability during operation at high temperature with the material subjected to large temperature gradients and electrical current. Material degradation has been encountered not only in recent high-performance materials such as SnSe, Cu 2 Se and Zn 4 Sb 3 (Li et al, 2016;Brown et al, 2014;Hung et al, 2017;Yin et al, 2010), but even in inorganic clathrates usually considered as extremely stable compounds (Reardon et al, 2017). TE energy harvesting relies strongly on optimizing operational reliability without compromising energy-conversion efficiency.…”

“…This primarily involves powder X-ray diffraction (PXRD) studies at elevated temperatures, or thermal cycling, using various atmospheres (Jørgensen et al, 2018a(Jørgensen et al, , 2018bPedersen & Iversen, 2008;Pedersen et al, 2006Pedersen et al, , 2010Fischer et al, 2018;Reardon et al, 2017;. Some studies have exposed TE materials to (semi)realistic conditions but they have not simultaneously characterized the structural or TE properties (operando) (Reardon et al, 2017;Hung et al, 2017;Yin et al, 2014). Operando studies are well established e.g.…”