Univerzita Pardubice Fakulta chemicko- technologická

Univerzita Pardubice

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Publikace detail

Vacancies in SnSe single crystals in a near-equilibrium state

Autoři: Šraitrová Kateřina | Čížek J | Drašar Čestmír

Rok: 2019

Druh publikace: ostatní - přednáška nebo poster

Strana od-do: nestránkováno

Tituly:

Jazyk	Název	Abstrakt	Klíčová slova
eng	Vacancies in SnSe single crystals in a near-equilibrium state	We investigated type and concentration of intrinsic vacancies in single crystalline SnSe as a function of annealing temperature. The investigation is based on positron annihilation spectroscopy combined with transport measurements. Two types of single-vacancies were found in SnSe single crystals. Tin vacancies VSn dominate at the temperatures ≤ 500 K, while selenium vacancies VSe and vacancy clusters VSn + nVSe dominate at higher temperatures ≥ 600 K. This implies that actual stoichiometry of SnSe is temperature dependent and SnSe prefers a Se-rich composition at low temperatures and a Se-poor composition at higher temperatures. Se liberated from the structure with increasing temperature further reacts with SnSe and produces SnSe2. The vacancy clusters survive the α→β transition at ≈800 K and grow in size with temperature. The concentration of VSe and VSn + nVSe increases with temperature as well as the thermoelectric performance indicating the connection between excellent thermoelectric properties of SnSe and these point defects. The defects might help in increasing the power factor of the material due to a local increase in the DOS or an extra energy-dependent scattering. Further, they induce an enhanced scattering of phonons and hence a drop in thermal conductivity. We hypothesize that the concentration of defects remains much higher in single crystals than in polycrystals. The reason might be that such defects (being created due to the variation in the equilibrium stoichiometry with temperature) can accumulate at grain boundaries in PC while staying within the bulk in SC. The defects formed within the SC bulk keep their nanoscopic nature; hence, they can dissolve and precipitate upon cycling repeatedly.	thermoelectricity, SnSe, single crystals, vacancies, positron anihilation