7908

7356

كارشناسي ارشد

ماده چگال

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1391

هشت،78ص.: مصور،جدول،نمودار﴿رنگي﴾

ص.ع.به فارسي و انگليسي

هادي اكبرزاده

جواد هاشمي فر

4/6/92

داخلي: مهدي رنجبر

فيزيك

ID7356

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

82 Ab initio study of structural electronic and thermoelectric properties of AgSbSe2 crystal Shima Sharifi Najafabadi sh sharifi@ph iut ac ir 02 01 2013 Department of physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Persian Supervisor Prof H Akbarzadeh Abstract Global increase in energy consumption and running out of fossil resources of the earth has stimulated scientists to search for new energy resources The direct conversion of heat to electricity by using modern thermoelectric materials is nowadays considered as a possible energy resource which may have also impact on global warming By assembling appropriate thermoelectric generators around the exhaust pipe of the automobile some part of the waste heat may be recycled into electric power usable by cooling chamber or fridge of the vehicle The major challenges in manufacturing this type of generators are cost and efficiency of thermoelectric materials The efficiency of a thermoelectric generator through the dimensionless figure of merit ZT is associated with the electrical conductivity the Seebeck coefficient the thermal conductivity and the temperature T The ternary chalcogenides AgSbQ2 Q Te Se S are among favorite materials used in manufacturing thermoelectric segments that inherently have high Seebeck coefficient and electrical conductivity and low thermal conductivity which may be further improved by doping impurities Because of the similar scattering properties of the Ag and Sb atoms various X ray and neutron diffraction experiments have not been able to accurately determine atomic configuration of these systems although all measurements conform the rock salt crystal structure of this system Hence we have considered five possible crystal structures in this work In this study structural electronic and thermoelectric properties of AgSbSe2 crystal is investigated by using first principles computations The structural and electronic properties of AgSbSe2 crystal is calculated in the framework of density functional theory and GGA PBE approximation by using pseudopotential method We have used the PWSCF code from the computational QUANTUM ESPRESSO package in which the plane waves are used as the basis set for expansion of the Kohn Sham wave functions We used norm conserving and scalar relativistic pseudo potentials We considered five possible crystal structures of AgSbSe2 compound R3m Fd3m I41 amd P4 mmm and Fm3m to find out its stable structure equilibrium lattice parameters Bulk modules and cohesive energy In the next step the thermoelectric properties of different structures are calculated in the framework of the semi classical Boltzmann transport theory using Wannier90 and BoltzTraP codes and are compared with the experimental data By comparison between calculated electrical conductivity and experimental data the approximate value of relaxation time can be estimated PDF created with pdfFactory trial version www pdffactory com

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