Spherical hexagonal tellurium nanocrystals: Fabrication and size-dependent structural phase transition at high pressure

Single-crystalline spherical nearly monodisperse tellurium (Te) nanocrystals (NCs) with average diameters of 20 and 90 nm, respectively, have been fabricated for the first time by a facile solution sonochemistry process. The structural characterizations show that the as-synthesized Te NCs have pure hexagonal structure, as revealed by x-ray diffraction (XRD), selected-area electron diffraction (SAED), energy-dispersive x-ray (EDX) spectroscopy, and high-resolution transmission electron microscopy (HRTEM) methods. The size-dependent structural phase transition of Te NCs up to the high pressure of 20 GPa has been investigated in a diamond anvil cell using resistance measurement at room temperature, and compared with the behavior of bulk Te under identical conditions. The experimental results indicate that 20 nm Te NCs, 90 nm NCs, and bulk Te all undergo two phase transitions up to 20 GPa, their respective transition pressures being about 7.2 and 10.3 GPa, 5.9 and 8.8 GPa, and 4.0 and 6.8 GPa. This indicates that the phase transition pressures are higher for the smaller NCs. In this paper we discuss the size-dependent structural phase transitions, the sluggishness of the phase transition process, and the fluctuating properties of the phase transition products at high pressure. The present work might open an avenue to real-time detection of the dynamics of the phase transition in bulk and nanoscale materials at high pressure, and also could serve as a guide to tailoring the microscopic properties of materials.