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Semi-conducteurs polaires : Etude des propriétés structurales, vibrationnelles et thermodynamiques
| Content Provider | Semantic Scholar |
|---|---|
| Author | Souadkia, M. |
| Copyright Year | 2013 |
| Abstract | We present ab initio calculations of structurals, lattice dynamicals, thermodynamic properties of SrX (X = S, Se, Te and O)and their pressure dependence in both B1 (NaCl) and B2 (CsCl) phases. Static calculations predict the B1 B2 transition to occur at 17.7, 13.6, 12.3 and 30.6 GPa for SrS, SrSe, SrTe and SrO, respectively. The inclusion of zero point vibrations lowers these values. At zero pressure, the calculated phonon dispersions agree well with the measured ones for the B1 phase of SrO and at Γ point of SrS and SrSe, respectively. A pressure induced soft transverse acoustic (TA) phonon mode is identi ed at the zone boundary X point of the Brillouin zone of all compounds. The B2 phase is stable at high pressure. The Born e ective charge and the electronic dielectric constants are calculated and also evaluated in function of the pressure. We have also used the calculated the dispersions in conjunction with the quasi harmonic approximation to predict temperature and pressure dependance of various quantities such as the thermal expansion coe cient, the bulk modulus, entropy and the heat capacity. Our results for the thermal expansion coe cient show that it decreases with pressure. The predicted transition pressure decreases with temperature. We have also studies the e ect of composition (x) on structural properties of SrS1−xSex, SrS1−xTex and SrSe1−xTex, for B1 phase. By using the density functional perturbation theory (DFPT) and the virtual crystal approximation (VCA). The variation of the phonon frequencies at the high symmetry points, the electronic and static dielectric constant, the Born e ective charge and the elastic constants as a function of the composition (x) is also studied. All these properties follow a quadratic law in x and the value of the bowing parameter for SrS1−xTex is large than the obtained for the two other alloys. The structural and elastic properties for simple cubic supercells with x = 0.25, x = 0.5 and x = 0.75 have been computed and are in good agreement with those obtained from VCA and others calculations. keywords : II-VI compounds ; Phonon ; Thermodynamic properties ; Phase transition ; Abinitio calculation ; Virtual-crystal approximation ; Supercell. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://dspace.univ-guelma.dz:8080/xmlui/bitstream/handle/123456789/183/thesis_doctorat-souadkia.pdf?isAllowed=y&sequence=1 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
