Publications (7)5.49 Total impact
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Article: Lattice stability and formation energies of intrinsic defects in Mg(2)Si and Mg(2)Ge via first principles simulations.
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ABSTRACT: We report an ab initio study of the semiconducting Mg(2)X (with X = Si, Ge) compounds and in particular we analyze the formation energies of the different point defects with the aim of understanding the intrinsic doping mechanisms. We find that the formation energy of Mg(2)Ge is 50% larger than that of Mg(2)Si, in agreement with the experimental tendency. From a study of the stability and the electronic properties of the most stable defects, taking into account the growth conditions, we show that the main cause of the n doping in these materials comes from interstitial magnesium defects. Conversely, since other defects acting like acceptors such as Mg vacancies or multivacancies are more stable in Mg(2)Ge than in Mg(2)Si, this explains why Mg(2)Ge can be of n or p type, in contrast to Mg(2)Si. The finding that the most stable defects are different in Mg(2)Si and Mg(2)Ge and depend on the growth conditions is important and must be taken into account in the search for the optimal doping to improve the thermoelectric properties of these materials.Journal of Physics Condensed Matter 12/2012; 25(3):035403. · 2.55 Impact Factor -
Article: Physical properties of thermoelectric zinc antimonide using first-principles calculations
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ABSTRACT: We report first principles calculations of the structural, electronic, elastic and vibrational properties of the semiconducting orthorhombic ZnSb compound. We study also the intrinsic point defects in order to eventually improve the thermoelectric properties of this already very promising thermoelectric material. Concerning the electronic properties, in addition to the band structure, we show that the Zn (Sb) crystallographically equivalent atoms are not exactly equivalent from the electronic point of view. Lattice dynamics, elastic and thermodynamic properties are found to be in good agreement with experiments and they confirm the non equivalency of the zinc and antimony atoms from the vibrational point of view. The calculated elastic properties show a relatively weak anisotropy and the hardest direction is the y direction. We observe the presence of low energy modes involving both Zn and Sb atoms at about 5-6 meV, similarly to what has been found in Zn4Sb3 and we suggest that the interactions of these modes with acoustic phonons could explain the relatively low thermal conductivity of ZnSb. Zinc vacancies are the most stable defects and this explains the intrinsic p-type conductivity of ZnSb.07/2012; -
Article: Phase stability and physical properties of Ta5Si3 compounds from first-principles calculations,
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ABSTRACT: We present a study of the thermodynamic and physical properties of Ta5Si3 compounds by means of density functional theory based calculations. Among the three different structures (D8m, D8l, D88), the D8l structure (Cr5B3-prototype) is the low temperature phase with a high formation enthalpy of -449.20kJ/mol, the D8m structure (W5Si3-prototype) is the high temperature phase with a formation enthalpy of -419.36kJ/mol, and the D88 structure (Mn5Si3-prototype) is a metastable phase. The optimized lattice constants of the different Ta5Si3 compounds are also in good agreement with the experimental data. The electronic density of states (DOS) and the bonding charge density have also been calculated to elucidate the bonding mechanism in these compounds and the results indicate that bonding is mostly of covalent nature. The elastic constants of the D8m and D8l structures have been calculated together with the different moduli. Finally, by using a quasiharmonic Debye model, the Debye temperature, the heat capacity, the coefficient of thermal expansion and the Gr\"uneisen parameter have also been obtained in the present work. The transformation temperature (2303.7K) between the D8m and the D8l structures has been predicted by means of the Gibbs energy, and this predicted temperature (2303.7K) is close to the experimental value (2433.5K).11/2011; -
Article: Effect of doping on the thermoelectric properties of thallium tellurides using first principles calculations
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ABSTRACT: We present a study of the electronic properties of Tl5Te3, BiTl9Te6 and SbTl9Te6 compounds by means of density functional theory based calculations. The optimized lattice constants of the compounds are in good agreement with the experimental data. The band gap of BiTl9Te6 and SbTl9Te6 compounds are found to be equal to 0.589 eV and 0.538 eV, respectively and are in agreement with the available experimental data. To compare the thermoelectric properties of the different compounds we calculate their thermopower using Mott's law and show, as expected experimentally, that the substituted tellurides have much better thermoelectric properties compared to the pure compound.11/2011; -
Article: Physical properties of thallium-tellurium based thermoelectric compounds using first-principles simulations.
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ABSTRACT: We present a study of the thermodynamic and physical properties of Tl(5)Te(3), BiTl(9)Te(6), and SbTl(9)Te(6) compounds by means of density functional theory based calculations. The optimized lattice constants of the compounds are in good agreement with the experimental data. The electronic density of states and band structures are calculated to understand the bonding mechanism in the three compounds. The indirect band gaps of BiTl(9)Te(6) and SbTl(9)Te(6) compounds are found to be equal to 0.256 and 0.374 eV, respectively. The spin-orbit coupling has important effects on the electronic structure of the two semiconducting compounds and should therefore be included for a good numerical description of these materials. The elastic constants of the three compounds have been calculated, and the bulk modulus, shear modulus, and Young's modulus have been determined. The change from ductile to brittle behavior after Sb or Bi alloying is related to the change of the electronic properties. Finally, the Debye temperature and longitudinal, transverse, and average sound velocities have been obtained.The Journal of Physical Chemistry A 08/2011; 115(31):8761-6. · 2.95 Impact Factor -
Article: De l'importance des modes optiques de basse energie dans les materiaux thermoelectriques
Materiaux 2010. -
Article: Phase stability and physical properties of Ta_ {5} Si_ {3} compounds from first-principles calculations
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ABSTRACT: We present a study of the thermodynamic and physical properties of Ta5Si3 compounds by means of density-functional theory based calculations. Among the three different structures (D8m, D8l, D88), the D8l structure (Cr5B3 prototype) is the low-temperature phase with a high formation enthalpy of −449.20 kJ/mol, the D8m structure (W5Si3 prototype) is the high-temperature phase with a formation enthalpy of −419.36 kJ/mol, and the D88 structure (Mn5Si3 prototype) is a metastable phase. The optimized lattice constants of the different Ta5Si3 compounds are also in good agreement with the experimental data. The electronic density of states and the bonding charge density have also been calculated to elucidate the bonding mechanism in these compounds and the results indicate that bonding is mostly of covalent nature. The elastic constants of the D8m and D8l structures have been calculated together with the different moduli. Finally, by using a quasiharmonic Debye model, the Debye temperature, the heat capacity, the coefficient of thermal expansion, and the Grüneisen parameter have also been obtained in the present work. The transformation temperature (2303.7 K) between the D8m and the D8l structures has been predicted by means of the Gibbs energy, and this predicted temperature (2303.7 K) is close to the experimental value (2433.5 K).Phys. Rev. B. 80(10).
Top co-authors
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Institutions
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2012
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Université de Montpellier 2
Montpellier, Languedoc-Roussillon, France
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2011
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Guangxi University
Nanning, Guangxi Zhuangzu Zizhiqu, China
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