Nanoscale stabilization of new phases in the PbTe-Sb₂Te ₃ System: Pb_mSb_{2 n}Te_{m +3 n} nanocrystals

A series of novel rock-salt-type Pb_mSb_2nTe _m+3n nanocrystals (m = 2, 3, 4, 6, 8, and 10; n = 1 and 2) were successfully prepared using a colloidal synthesis route. These materials are stable only on the nanoscale and have no bulk analogues. Elemental compositions were determined using scanning transmission electron microscopy/energy- dispersive X-ray spectroscopy (STEM/EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The nanocrystals exhibit well-defined band energies in the mid-IR region that are nearly independent of their atomic compositions. Pb_mSb_2nTe_m+3n nanocrystals behave as metastable homogeneous solid solutions at room temperature and tend to phase separate into the respective binary PbTe + Sb₂Te₃ at 300 C. Furthermore, pair distribution function (PDF) analysis suggests that the local structure of these Pb_mSb_2nTe_m+3n nanocrystals is distorted with respect to the rock-salt structure.