Continuous phase transition in thermoelectric Zn4Sb3

Heterogeneous transformation is a phase transition with distinct characteristics that can have abrupt effects on the thermoelectric performance in a narrow temperature range. The continuous phase transition is difficult to identify, and its influence on the thermoelectric properties is unclear. Zn4Sb3 is a high-performance thermoelectric material with various phase transitions. Its complex temperature dependent crystal structure influences the understanding of its transport mechanism. Following vacuum melting, spark plasma sintering was used to prepare several Zn4Sb3 samples of varying densities. The non-dense Zn4Sb3 samples exhibited a dramatic improvement in thermoelectric performance in the temperature range of 425-550 K. In situ hot stage experiments and fracture morphology observations revealed that Zn4Sb3 precipitates Zn in grain boundaries and holes. The reversible heat capacity and enthalpy analyses showed that Zn4Sb3 undergoes a continuous phase transition in this temperature range. Molecular dynamics simulations confirmed this phenomenon. The decrease in potential energy was accompanied by the appearance of many nanophases, stress regions, and sub-grain boundaries. These microstructural changes were responsible for the rapid improvement in thermoelectric performance. After the phase transition, the potential energy began to increase, and the Zn4Sb3 lattice reabsorbed the Zn atoms at the grain boundaries, avoiding further decomposition of Zn4Sb3. Because the continuous phase transition can continue over a wide temperature range, the improvement of thermoelectric performance caused by the continuous phase transition has potential application value. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study found that Zn4Sb3 material undergoes a continuous phase transition within a specific temperature range, resulting in a significant improvement in thermoelectric performance. Experiments and analysis revealed that, during the continuous phase transition, there were changes in the crystal structure of Zn4Sb3, which in turn affected its thermoelectric properties.