Vacancies in SnSe single crystals in a near-equilibrium state

Abstract

The development of intrinsic vacancies in SnSe single crystals was investigated as a function of annealing temperature by means of positron annihilation spectroscopy accompanied by transport measurements. It has been demonstrated that two types of vacancies are present in single-crystalline SnSe. While Sn vacancies dominate in the low-temperature region, Se vacancies and vacancy clusters govern the high-temperature region. These findings are supported by theoretical calculations enabling direct detection and quantification of the most favorable type of vacancies. The experiments show that Sn vacancies couple with one or more Se vacancies with increasing temperature to form vacancy clusters. Interestingly, the clusters survive the α→β transition at ≈800 K and even grow in size with temperature. The concentration of both Se vacancies and vacancy clusters increases with temperature, similar to thermoelectric performance. This indicates that the extraordinary thermoelectric properties of SnSe are related to point defects. We suggest that either these defects vary the band structure in favor of high thermoelectric performance or introduce an energy-dependent scattering of free carriers realizing, in fact, energy filtering of the free carriers. Cluster defects account for the glasslike thermal conductivity of SnSe at elevated temperatures.

Anomalous Raman modes in tellurides

“…12 Therefore, Se and Te nanoclusters or fewlayer films can occur during crystal growth, especially near the sample edges, as proved in SnSe by positron annihilation spectroscopy. 79 It has also been proved that oxidation at ambient conditions seems to favor the presence of the ARMs. 18,21 On the other hand, it has also been shown that treatment with acid agents, like HCl, HF, and HNO3 lead to formation of Te layers in CdTe, while dilution of bromine in methanol removes the Te layer.…”

In Situ Detection of Local Structure Transformation of 2D SnSe Nanosheets through Nanothermomechanical Behavior

“…According to the results described earlier, a microcosmic mechanism of heat-induced surface structure transformation from SnSe into SnSe 2 could be inferred. As the Sn vacancy defect is the common defect in SnSe, [6,18,19] the migration of Sn ion will format the Schottky defect and nanosized Sn congeries upon the surface of SnSe. The sticky surface of the SnSe nanosheet is due to the semimolten Sn congeries.…”

SnSe:Kx intermetallic thermoelectric polycrystals prepared by arc-melting

“…Successful thermoelectric generators have been made based on SnSe very recently [64]. The effects of vacancy on the thermoelectric properties have been studied in detail [65][66][67][68]. Applied pressure transforms SnSe into a semimetal [69].…”