Creep of Thermoelectric Materials

Muath Mohammed Al Malki

co-advised with Prof. Jeffery Snyder

Over 60% of thermal energy is dissipated as waste heat, some of which can be collected and converted into electricity with thermoelectric materials (TE) via the Seebeck effect. One current applications of TE in power generation is the use of radioisotopes thermoelectric generators in space probes and satellites.

Thermally- and mechanically induced stresses can deteriorate the mechanical and the thermoelectric performance of TE. In particular, creep deformation can limit the mechanical lifetime of installed TE modules. Also, the thermoelectric performance, represented by the figure of merit zT, was shown to drop down by 20-30% due to the increase of the dislocations density and the elimination of the high-angle grain boundaries, a result of creep deformation. In this research, we are further exploring the relation between mechanical degradation and deterioration in thermoelectric performance in various thermoelectric classes (Skutterudites, Half Heusler..).Our recent in-situ electrical resistivity- creep measurement of doped PbTe reveals the direct role of complex dislocation networks and subgrain structures on the continuous increase in the electrical resistivity, in contrary to previous findings.

A schematic of types of stresses that may affect a TE module. One TE leg is shown here, but the same stresses impact the whole module

Double-logarithmic plots of minimum creep strain rate vs. compressive stress. The plot compiles compressive creep data for all TE materials tested to date, listing testing temperature (spanning 400-600șC), homologous temperature (0.51-0.90), and stress exponent for each alloy. For comparison, creep data for Sn-37Pb solder at 120șC is added.

A schematic drawing for the in-situ 4-points conductivity measurement circuit used in this study, showing both the voltage (v) and current (I) leads positions (Top left). A picture of the real setup is shown to the top right. Time dependence of in-situ electrical conductivity (middle left) and resistivity (middle right) plotted as a function of engineering strain. The dotted lines indicate change of the applied compressive stress, the value of which is depicted within each stress range in MPa. TEM observation of formation of subgrain structures and complex dislocation networks as a result of dislocation dominated creep deformation of doped PbTe (bottom)

Related Publications

  1. Guan, Z. P., & Dunand, D. C. (2013). Compressive creep behavior of cast Bi2Te3. Materials Science and Engineering: A, 565, 321-325.
  2. Li, C. C., Snyder, G. J., & Dunand, D. C. (2017). Compressive creep behaviour of hot-pressed PbTe. Scripta Materialia, 134, 71-74.
  3. Michi, R. A., Kim, G., Kim, B. W., Lee, W., & Dunand, D. C. (2018). Compressive creep behavior of hot-pressed Mg1. 96Al0. 04Si0. 97Bi0. 03. Scripta Materialia, 148, 10-14.
  4. Chang, M. C., Agne, M. T., Michi, R. A., Dunand, D. C., & Snyder, G. J. (2018). Compressive creep behavior of hot-pressed GeTe based TAGS-85 and effect of creep on thermoelectric properties. Acta Materialia, 158, 239-246.
  5. Al Malki, M. M., Qiu, Q., Zhu, T., Snyder, G. J., & Dunand, D. C. (2019). Creep behavior and postcreep thermoelectric performance of the n-type half-Heusler alloy Hf0. 3Zr0. 7NiSn0. 98Sb0. 02. Materials Today Physics, 9, 100134.
  6. Al Malki, M. M., Shi, X., Qiu, P., Snyder, G. J., & Dunand, D. C. (2021). Creep behavior and post-creep thermoelectric performance of the n-type Skutterudite alloy Yb0. 3Co4Sb12. Journal of Materiomics, 7(1), 89-97.
  7. Al Malki, M. M., Snyder, G. J., & Dunand, D. C. (2023). Mechanical behavior of thermoelectric materials, a perspective. International materials reviews [accepted]

Funding support

  1. King Fahd University for Petroleum and Minerals Scholarship [ KFUPM]