Results

Results:

2011 Oct. - Dec.

- The choice of exchange-correlation functional (considering LDA/GGA, B1-WC hybrid, ...)
The structural and electronic properties of bulk SrTiO₃ are described with better accuracy within B1-WC hybrid fucntional than those within usual simple functionals. In order to have a complete theoretical description, we studied also the thermoelectric (TE) properties (transport coefficients: electrical conductivity σ , Seebeck coefficient ("thermopower") S and power factor PF=S²σ) of bulk SrTiO₃ within B1-WC hybrid fucntional and usual simple functionals. Transport coefficients were estimated within Boltzmann transport formalism and constant relaxation time approximation.

- Comparison of the differences in the electronic properties of bulk SrTiO₃ and its alloys with La, Nb, V
For SrTiO₃ based oxides, the promising TE properties were found at very large n-type doping concentrations (n ~ 10²¹ cm^-3, concentration which is two orders of magnitudes greater than that of typical TE materials, PbTe, Bi₂Te₃). At these large concentrations, the rigid band approximation (the electronic states of SrTiO₃ doped oxides are considered the same as those of bulk SrTiO₃) may not hold. The theoretical estimations of TE properties (underestimation of power factors PF) within the different functionals using the electronic states generated by different first-principles codes show that this approximation is not valid. At these large concentrations, the doping elements (ex. La, Nb, V) have to be explicitly included in the electronic calculations by considering supercells containing the doping elements.

- The choice of appropriate supercells

2012 Jan. - Dec.

- Transport properties of bulk SrTiO₃ and its alloys (SrTi_1-xNb_xO₃ and SrTi_1-xV_xO₃)
The choice of 3x3x3 supercells (135 per atoms/cell) with the electronic concentration n ~ 1.2x10²¹ cm^-1, containing explicitly the doping elements. Electronic properties analysis (density of states DOS) shows that the electronic states close to Fermi level (chemical potential) are changed with respect to SrTiO₃ bulk. Indeed at these large concentrations the rigid band approximation does not hold.

- Band structure engineering in the nanostructures formed by (SrTiO₃)_m-KNbO₃ and (SrTiO₃)_m-LaVO₃ perovskite series
We have considered the superlattices SL: (SrTiO₃)_m(KNbO₃)₁ and (SrTiO₃)_m(LaVO₃)₁ with m=1,5 for which we studied the structural, electronic and thermoelectric (TE) properties. We studied the effect of quantum confinement on the TE properties (power factors PF). Band structure engineering in (SrTiO₃)_m(LaVO₃)₁ SL, is able to generate a narrow energy distribution with a significant weight, which gives impresive power factors PF.

2013 Jan. - Dec.

- Band structure engineering in the nanostructures formed by perovskite series (SrTiO₃)_m-KNbO₃ and (SrTiO₃)_m-LaVO₃
Study of octahedral rotations
Study of phonon properties
Analysis of electronic states responsible for the impressive power factors PF's of p-type.
Writting of an article related to the very good results of (SrTiO₃)_m(LaVO₃)₁ SL in order to be published in a high impact international journal.

- Transport properties of SrTiO₃ based alloys (SrTi_1-xNb_xO₃ and SrTi_1-xV_xO₃)
Study of TE properties considering 3x3x3 supercells containing explicitely the doping elements.

- Band structure engineering of SrTiO₃ alloys (SrTi_1-xNb_xO₃ and SrTi_1-xV_xO₃)

- Design of high performance SrTiO₃-based TE oxides
New TE materials, which possess intrinsically a narrow energy distribution with significalt weight in electronic transport.

2014 Jan. - Oct.

- Thermoelectric proprerties of Sr and Co based AO[ABO₃]_m Ruddlesden-Popper naturally ordered compounds
The study of electronic and transport properties of the Ruddlesden-Popper SrO[SrTiO₃]_m (m=1, 2), and SrO[SrCoO₂F]₁ compounds.

- TE properties of the 2-dimensional electron gaz (2-DEG) formed in the SrTiO₃ superlattices (SL)
The structural, electronic and TE properties were already studied for 2-DEG formed in the SrTiO₃/SrRuO₃ SL. The results were published in the articles Phys. Rev. B 86, 085305 (2012) and Phys. Rev. Lett. 108, 107003 (2012).

Final Synthetic Scientific Raport 2011-2014

ISI Articles:

1. P. Garcia-Fernandez, M. Verissimo-Alves, D. I. Bilc, P. Ghosez, and J. Junquera, First-principles modeling of the thermoelectric properties of SrTiO₃/SrRuO₃ superlattices, PHYSICAL REVIEW B 86, 085305 (2012). DOI: 10.1103/PhysRevB.86.085305
Article related to the first-principles modeling of SrTiO₃ based oxides for thermoelectric applications.

2. M. Verissimo-Alves, P. Garcia-Fernandez, D. I. Bilc, P. Ghosez, and J. Junquera, Highly Confined Spin-Polarized Two-Dimensional Electron Gas in SrTiO₃/SrRuO₃ Superlattices, PHYSICAL REVIEW LETTERS 108, 107003 (2012). DOI: 10.1103/PhysRevLett.108.107003)
Article related to the first-principles modeling of SrTiO₃/SrRuO₃ superlattices using B1-WC method.

3. E. Drugun, D. I. Bilc, S. Ciraci, and P. Ghosez, Hydrogen-Saturated Silicon Nanowires Heavily Doped with Interstitial and Substitutional Transition Metals JOURNAL OF PHYSICAL CHEMISTRY 116, 15713 (2012). DOI: 10.1021/jp303142u
Article related to the study (testing) of 1-dimensional nanostructures using B1-WC method.

4. D. I. Bilc, G. Hautier, D. Waroquiers, G-M. Rignanese, and P. Ghosez, Large thermoelectric power factors in bulk semiconductors by band engineering of highly-directional electronic states , Submitted to PHYSICAL REVIEW LETTERS; e-print archive: cond-mat/1405.4685 .
Article related to the design of new high performance TE materials with large TE power factors.

Conference Presentations:

1. D. I. Bilc, C. Morari, and C. Floare, First-Principles Modelling of SrTiO3 Based Oxides for Thermoelectric Applications, European MRS spring Meeting 2012, Strasbourg, France.

2. D. I. Bilc, and Ph. Ghosez, Thermoelectric properties of Fe based full Heusler compounds, University of Liege, Feb 2012, Liege, Belgium.

3. D. I. Bilc, F. D. Novaes, J. Iniguez, P. Ordejon, and P. Ghosez, Tunneling Across a Ferroelectric Barrier : A First-Principles Study, 7-th International Conference on Advanced Materials, ROCAM 2012, Brasov, Romania.

4. D. I. Bilc, C. Morari, C. Floare, and P. Ghosez, Band Structure Engineering of Thermoelectric SrTiO3 Based Oxides with large Power Factors, 32-nd International Conference on Thermoelectricity, ICT 2013, Kobe, Japan.

5. D. I. Bilc, and P. Ghosez, First-principles accurate prediction of the electronic and structural properties of ferroelectric oxide bulks and nanostrustructures, COST Workshop: Early Stage Researchers and The tenth Students' Meeting 2013, Novi Sad, Serbia.

6. C Floare, C. Morari, D. I. Bilc, and P. Ghosez, First-Principles Modelling of SrTiO3 Based Oxides for Thermoelectric Applications, COST Workshop: Early Stage Researchers and The tenth Students' Meeting 2013, Novi Sad, Serbia.

6. D. I. Bilc, C. Morari, C. Floare, and P. Ghosez, Impressive thermoelectric power factors in SrTiO₃ based nanostructures by band engineering of highly-directional electronic states , Electroceramics XIV 2014, Bucharest, Romania.

7. D. I. Bilc, C. Morari, C. Floare, and P. Ghosez, Impressive thermoelectric power factors in SrTiO₃ based nanostructures by band engineering of highly-directional electronic states , COST MP1308 - TO BE 2014, Rome, Italy.

INCDTIM