In Situ Investigation of the Phase Transition at the Surface of Thermoelectric PbTe with van der Waals Control

Abstract

The structure of thermoelectric materials largely determines the thermoelectric characteristics. Hence, a better understanding of the details of the structural transformation process/conditions can open doors for new applications. In this study, the structural transformation of PbTe (a typical thermoelectric material) is studied at the atomic scale, and both nucleation and growth are analyzed. We found that the phase transition mainly occurs at the surface of the material, and it is mainly determined by the surface energy and the degree of freedom the atoms have. After exposure to an electron beam and high temperature, high-density crystal-nuclei appear on the surface, which continue to grow into large particles. The particle formation is consistent with the known oriented-attachment growth mode. In addition, the geometric structure changes during the transformation process. The growth of nanoparticles is largely determined by the van der Waals force, due to which adjacent particles gradually move closer. During this movement, as the relative position of the particles changes, the direction of the interaction force changes too, which causes the particles to rotate by a certain angle.

Nanoscale fabrication of heterostructures in thermoelectric SnTe

“…Note that the appearance of the vdWs gaps shrinks the planar spacing. 18,21,38,39 Based on the experimental observations, the unit cell of h-SnTe is proposed in Fig. 3a in hexagonal representation, which is composed of six Sn atoms and six Te atoms.…”

“…In addition, the vdWs gaps in h-SnTe can decouple the transmission of carriers and phonons by effectively transferring carriers while scattering phonons. 18,39,53 In this work, the electron beam can serve as a tool for fabricating h-SnTe/β-SnTe heterostructures at the atomic scale. For instance, nanopillars of h-SnTe can be prepared in the β-SnTe matrix, as demonstrated in Fig.…”

“…17 The phase transition can be obtained without changing the stoichiometry of the materials, e.g., the transition of a cubic structure (Fm3 ˉm) to an orthorhombic structure (Pnma) in thermoelectric PbTe exposed to electron beams and high temperatures in a transmission electron microscope (TEM). 18 In this respect, introducing local phase changes in materials offers a method for tailoring the thermoelectric properties of nanomaterials. Among the strategies for triggering phase changes in materials (e.g., heating 7 and laser excitation 19,20 ), the highly energetic electrons provide a facile way to manipulate the phase transition in materials at the atomic scale.…”

“…Among the strategies for triggering phase changes in materials (e.g., heating 7 and laser excitation 19,20 ), the highly energetic electrons provide a facile way to manipulate the phase transition in materials at the atomic scale. 18,[21][22][23] Among the thermoelectric materials, SnTe-based compounds have attracted considerable attention due to their having the same multiple valence bands as PbTe and their non-toxicity. 21,[24][25][26][27][28] In terms of crystal structure, apart from the † Electronic supplementary information (ESI) available.…”

Applications of Transmission Electron Microscopy in Phase Engineering of Nanomaterials

“…In addition to heating and biasing, − phase transitions of crystalline materials have also been investigated in situ in gas or liquid environments using TEM. For example, an environmental TEM microscope, despite its limited gas pressure, has been utilized to carry out in situ EELS studies of hydrogen-induced phase transitions in palladium nanocrystals .…”