Polycrystalline Mg{sub 2}Si thin films: A theoretical investigation of their electronic transport properties

Journal Article · Fri May 15 04:00:00 EDT 2015 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2014.12.014· OSTI ID:22475591

Balout, H. ^[1]; Record, M. -C. ^[2]

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1. MADIREL, Aix-Marseille University and CNRS, Avenue Normandie-Niemen, 13397 Marseille (France)
2. IM2NP, Aix-Marseille University and CNRS, Avenue Normandie-Niemen, 13397 Marseille (France)

The electronic structures and thermoelectric properties of a polycrystalline Mg{sub 2}Si thin film have been investigated by first-principle density-functional theory (DFT) and Boltzmann transport theory calculations within the constant-relaxation time approximation. The polycrystalline thin film has been simulated by assembling three types of slabs each having the orientation (001), (110) or (111) with a thickness of about 18 Å. The effect of applying the relaxation procedure to the thin film induces disorder in the structure that has been ascertained by calculating radial distribution functions. For the calculations of the thermoelectric properties, the energy gap has been fixed at the experimental value of 0.74 eV. The thermoelectric properties, namely the Seebeck coefficient, the electrical conductivity and the power factor, have been determined at three temperatures of 350 K, 600 K and 900 K with respect to both the energy levels and the p-type and n-type doping levels. The best Seebeck coefficient is obtained at 350 K: the S{sub yy} component of the tensor amounts to about ±1000 μV K{sup −1}, depending on the type of charge carriers. However, the electrical conductivity is much too small which results in low values of the figure of merit ZT. Structure–property relationship correlations based on directional radial distribution functions allow us to tentatively draw some explanations regarding the anisotropy of the electrical conductivity. Finally, the low ZT values obtained for the polycrystalline Mg{sub 2}Si thin film are paralleled with those recently reported in the literature for bulk chalcogenide glasses. - Graphical abstract: Structure of the polycrystalline thin film of Mg{sub 2}Si. - Author-Highlights: • Polycrystalline Mg{sub 2}Si film has been modelled by DFT approach. • Thermoelectric properties have been evaluated by semi-classical Boltzmann theory. • The structure was found to be slightly disordered after relaxation. • The highest value of Seebeck coefficient reaches −1000 μV/K at 350 K. • The ZT value is estimated between 0.0175 at 350 K and 0.2 at 900 K.

• OSTI ID: 22475591
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Vol. 225; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CHARGE CARRIERS
CORRELATIONS
DENSITY FUNCTIONAL METHOD
ELECTRIC CONDUCTIVITY
ELECTRONIC STRUCTURE
ENERGY GAP
ENERGY LEVELS
EV RANGE
INTERMETALLIC COMPOUNDS
MAGNESIUM SILICIDES
POLYCRYSTALS
POWER FACTOR
RELAXATION TIME
SPATIAL DISTRIBUTION
TEMPERATURE DEPENDENCE
TENSORS
THERMOELECTRIC PROPERTIES
THIN FILMS
TRANSPORT THEORY