10142

756 دكتري

دكتري

فيزيك ماده چگال

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1393

[نه]، 115ص.: مصور، جدول

ص. ع. به فارسي و انگليسي

هادي اكبر زاده، جواد هاشمي فر

كيوان اسفرجاني

5/3/94

اكبر جعفري، محمدرضا محمدي زاده، فرهاد فضيله

فيزيك

ID756 دكتري

Investigation of thermoelectric and charge transfer properties by using Wannier functions Na seh Rezaei Badafshani n rezaee@ph iut ac ir Department of Physics Isfahan University of Technology Isfahan 84156 83111 IranDegree Ph D Language PersianSupervisors Prof H Akbarzadeh akbarzad@cc iut ac ir and Dr S J Hashemifar hashemifar@cc iut ac irAbstractThe Wannier functions provide a real representation of electronic ground state in real spaceand are obtained from the Fourier transformation of the Bloch functions The localized natureof Wannier functions can be exploited as convenient basis for describing the local phenomenasuch as orbital magnetization electrical polarization electronic transport intersite chargetransfer and the nature of chemical bonding The Wannier functions are minimal basis forconstruction of model Hamiltonian and can be used for accurate and fast interpolation of theband structure onto very ne meshes This is very useful for calculation of quantities likeSeebeck coe cient electrical conductivity ordinary and anomalous hall coe cient which aresensitive to the ne details of the band structure In this dissertation we investigate thermo electric properties of AgSbTe2 as an interesting thermoelectric material and the mechanismof charge transfer in double perovskites LnCu3 Fe4 O12 Ln lanthanides by using the Wan nier functions The Seebeck coe cients and electrical conductivity of AgSbTe2 are computed within Boltz mann semiclassical theory of transport and constant relaxation time approximation Theconventional exchange correlation functionals like GGA underestimate the band gap Inthis regard the band gap problem is considered by hybrid functional The computed Seebeckcoe cients at di erent values of the band gap and carrier concentration are compared withthe available experimental data to speculate a band gap of about 0 1 0 35 eV for AgSbTe2compound in agreement with our calculated electronic structure within the hybrid HSE Heyd Scuseria Ernzerhof functional The Fe Cu intersite charge transfer and Fe charge disproportionation are interesting phe nomena observed in some LnCu3 Fe4 O12 compounds containing light and heavy Ln atoms respectively In Wannier representation we nd that the strength of the crystal eld splittingand the relative energy ordering between Cu 3dxy and Fe 3d states are the key parametersdetermining the intersite charge transfer charge disproportionation in light heavy Ln com pounds We show that a change in the spin state is responsible for the intersite charge transferin the light Ln compounds At the high spin state such systems prefer an unusual Cu d8con guration whereas at the low spin state they retreat to the normal Cu d9 con gurationthrough a charge transfer from Fe to the Cu 3dxy Keywords Wannier functions Thermoelectric AgSbTe2 double perovskites LnCu3 Fe4 O12 intersite charge transfer charge disproportionation

هادي اكبر زاده، جواد هاشمي فر

كيوان اسفرجاني

اكبر جعفري، محمدرضا محمدي زاده، فرهاد فضيله