1 جامعة ابن زهر ~ أكادير IBN ZOHR UNIVERSITY ~ AGADIR CNRST 2011 Rabat June 16, 2011 جامعة التكنولوجيا ~ درسدن UNIVERSITY OF TECHNOLOGY ~ DRESDEN

11زهرزهرابنابنجامعةجامعةأكاديرأكاديرIBN ZOHR UNIVERSITY ~ AGADIRIBN ZOHR UNIVERSITY ~ AGADIR

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ددالتكنولوجياالتكنولوجياجامعةجامعةرسدنرسدن

UNIVERSITY OF TECHNOLOGY ~ DRESDENUNIVERSITY OF TECHNOLOGY ~ DRESDEN

Polydisciplinary Faculty Polydisciplinary Faculty IIBN BN ZZOHR OHR UUNIVERSITYNIVERSITY

OOUARZAZATE, UARZAZATE, MMOROCCOOROCCO

SSURFACE AND URFACE AND IINTERFACE NTERFACE EEFFECTS ONFFECTS ON

THETHE E ELECTRICAL AND LECTRICAL AND OOPTICAL PTICAL PPROPERTIES OF ROPERTIES OF BBaTiOaTiO33

Single Crystals and Ultrathin FilmsSingle Crystals and Ultrathin Films

Institute of Applied PhotophysicsInstitute of Applied PhotophysicsUUNIVERSITY OF NIVERSITY OF TTECHNOLOGYECHNOLOGY

DDRESDEN, RESDEN, GGERMANYERMANY

H. ChaibH. ChaibPolydisciplinary Faculty of OuarzazatePolydisciplinary Faculty of Ouarzazate

H. Chaib

Thank you Dear chairman.The present work concerns the surface and interface effects on the electrical and optical properties of BaTiO3 single crystals and ultrathin films.This work has been mainly acheived in the Institute of Applied Photophysics in the University of Thechnology in Dresden, Germany.


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IntroductionIntroduction

Aim of the WorkAim of the Work

• Electrical and Optical PropertiesElectrical and Optical Properties

Considered MagnitudesConsidered Magnitudes

• Crystalline DeformationsCrystalline Deformations

• Electronic PolarizabilitiesElectronic Polarizabilities

• Spontaneous Ionic ShiftsSpontaneous Ionic Shifts

• Static Effective ChargesStatic Effective Charges

Material InterestMaterial Interest

• Technological ApplicationsTechnological Applications

Physical PropertiesPhysical Properties

• PiezoelectricPiezoelectric

• Ferroelectric, DielectricFerroelectric, Dielectric

• Optic, Electro-opticOptic, Electro-optic

• PhotorefractivePhotorefractive

Aspect of the WorkAspect of the Work

TheoreticalTheoretical

Studied MaterialStudied Material

BaTiOBaTiO33

H. Chaib

The aim of this work which has a theoretical aspect is to study of the surface and interface effects on the electrical and optical properties of BaTiO3 single crystals and BaTiO3 ultrathin films on SrTiO3 substrate. This is by taking into account the crystalline deformations as well as the electronic polarizabilities, the spontaneous ionic shifts, and the static effective charges of the constituent ions.The studied material is BaTiO3 which has a very promising technological interest being seen its piezoelectric, ferroelectric, dielectric, optic, electro-optic, and photorefractive properties.Many of these applications are increasingly oriented towards thin film and superlattice geometries, where surface and interface properties are of growing importance.


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Unit Cell in the Cubic PhaseUnit Cell in the Cubic Phase Unit Cell in the Tetragonal PhaseUnit Cell in the Tetragonal Phase

[1][1] A. Toumanari, Ph.D. Thesis, University of Agadir, Morocco 1999.A. Toumanari, Ph.D. Thesis, University of Agadir, Morocco 1999.[2][2] K. Nakamura and W. Kinase, K. Nakamura and W. Kinase, J. Phys. Soc. JpnJ. Phys. Soc. Jpn. . 6161, 2114 (1992)., 2114 (1992).

GeneralitiesGeneralities

Structural Properties of BaTiOStructural Properties of BaTiO33

3

2

1

2

1

3

Ba

Ox

Ti

Oy

Oz

1

2

3

Ba +1.437

Ox -1.200

Ti +2.063

Oy -1.200

Oz -1.100

1

2

3

3

1

1

3

22

Ps

Z*[1,2]

H. Chaib

So, BaTiO3 is a ferroelectric oxide material with a perovskite structure.At high temperature, this material is paraelectric with a cubic structure in which the titanium is located in the center, the barium is located in the corners, and the oxygens are located in the faces.At room temperature, this material is ferroelectric with a tetragonal structure. In this structure the unit cell undergoes an elongation in the direction of the spontaneous polarization and a shortening in the other directions. Moreover, the titanium shifts in the direction of the spontaneous polarization and the oxygens shift in the opposite direction. Yet, all ions are effectively charged and their charges are 1.437 for barium, 2.063 for titanium, -1.2 for the oxygens Ox and Oy and -1.1 for the oxygen Oz.


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GeneralitiesGeneralities

Experimental Values at Room TemperatureExperimental Values at Room Temperature

Spontaneous Ionic Shifts:Spontaneous Ionic Shifts: ss33(Ti) = (Ti) = 0.05 Å0.05 Å

ss33(O(Oxx, O, Oyy) =) = -0.05 Å-0.05 Å

ss33(O(Ozz) =) = -0.09 Å-0.09 Å

Spontaneous PolarizationSpontaneous Polarization::[1][1] PPspnspn = = 0.28 C/m0.28 C/m22

Refractive IndicesRefractive Indices::[2][2] nnoo = = 2.3982.398

nnee = = 2.3122.312

[1][1] R. S. Cudney, J. Fousek, M. Zgonik, and P. Gunter, R. S. Cudney, J. Fousek, M. Zgonik, and P. Gunter, Appl. Phys. LettAppl. Phys. Lett. . 6363, 3399 (1993)., 3399 (1993).[2][2] A. R. Johnston and J. M. Weingart, A. R. Johnston and J. M. Weingart, J. Opt. Soc. AmJ. Opt. Soc. Am. . 5555, 828 (1965)., 828 (1965).

H. Chaib

So, these effective charges are coupled with the spontaneous ionic shifts which are important and their mesured values are 0.05 A for titanium, -0.05 A for the oxygens Ox and Oy, and -0.09 A for the oxygen Oz. These important ionic shifts lead to an important spontaneous polarization which is 0.28 C/m2. Furthermore, this material is uniaxe negative material having two refractive indices: an ordinary refractive index and an extraordinary refractive index. The ordinary refractive index, noted no, is refractive index of the light polarized perpendicular to the direction of the spontaneous polarization. The measured value of this refractive index is 2.39. The extraordinary refractive index, noted ne, is the refractive index of the light polarized in the same direction as the spontaneous polarization. The measured value of this refractive index is 2.31. These measured values are relative to the bulk single crystals. Apparently, in this work we are interested in studying the effects of the surface and interface on the spontaneous polarization and refractive indices of BaTiO3 single crystals and BaTiO3 ultrathin films on the SrTiO3 substrate.


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MICROSCOPIC MODELMICROSCOPIC MODEL

Orbital ApproximationOrbital Approximation Dipole-dipole ApproximationDipole-dipole Approximation

ModelModel

Bases of the ModelBases of the Model

H. Chaib

... For this aim, we used a microscopic model based upon two approximations: The orbital approximation and the dipole-dipole approximation.


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To Express the:To Express the:Electronic PolarizabilitiesElectronic Polarizabilities

as Function of the Local Fieldas Function of the Local Field

To Calculate the Local Electric Field To Calculate the Local Electric Field and thenand then

the Polarization of Each Unit Cellthe Polarization of Each Unit Cell

Spontaneous PolarizationSpontaneous Polarizationandand

Refractive IndicesRefractive Indices

ModelModel

Description of the ModelDescription of the Model

H. Chaib

So, as mentioned before, our model is based upon two approximations: the orbital approximation and the dipole-dipole approximation. The orbital approximation is used to express the first-, second-, and third-order electronic polarizabilities of the constituent ions as function of the local electric field. These expressions will be used in the dipole-dipole approximation in order to calculate the local electric field and then the polarization of each unit cell within the sample from which we deduce the spontaneous polarization and the refractive indices which are ascribed the unit cell and not to individual ions.


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EEEEEEp ~~~e EEEEEEp ~~~e

The Quantum Mechanical The Quantum Mechanical Variation MethodVariation Method

The Quantum Mechanical The Quantum Mechanical Variation MethodVariation Method

Dielectric Dielectric PolarizationPolarizationDielectric Dielectric

PolarizationPolarization

SpontaneousSpontaneousPolarizationPolarization

SpontaneousSpontaneousPolarizationPolarization

RefractiveRefractiveIndicesIndices

RefractiveRefractiveIndicesIndices

Lorentz RelationLorentz Relation

ModelModel

EquationsEquations

cav

5

2extloc 3

Er

prrrpEE

i i

iiiii cav

5

2extloc 3

Er

prrrpEE

i i

iiiii

H. Chaib

In more details, the orbital approximation, which is based upon the quantum mechanical variational method, allows us to get the analytical expressions of the first-, second-, and third-order electronic polarizabilites, respectively, alpha, beta, and gamma which are connected to the electronic dipole moment of the considered ion through this equation.The obtained expressions of these electronic polarizabilities will be used in the dipole-dipole approximation in order to calculate the components of the local electric field. In this approximation we start from the Loretz relation giving the expression of the local electric field. The first term in this relation represents the external elctric field, the second term represents the contribution to the local electric field of the dipole moments of all ions located inside the spherical Lorentz cavity and the last term represents the contribution to the local electric field of the surface of the spherical Lorentz cavity.By solving this equation we get teh components of the local electric field and the dielectric polarization from which we deduce the spontaneous polarization and refractive indices.


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Equations to SolveEquations to Solve

)(=)()(~~loc~,~

,~

3

1=

5

1=

nik

mjl

mnjikl

mlj

QES )(=)()(~~loc~,~

,~

3

1=

5

1=

nik

mjl

mnjikl

mlj

QES

lkl

mjlmn

jiklmlj E

ES

=)(

)( opt

~loc~,~

,*

~

3

1=

5

1=lk

l

mjlmn

jiklmlj E

ES

=)(

)( opt

~loc~,~

,*

~

3

1=

5

1=

Spontaneous PolarizationSpontaneous Polarization

Refractive IndicesRefractive Indices


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Application PortingApplication Porting

Application characteristics:Application characteristics:* written in fortran f77;* written in fortran f77;* uses OpenMP for parallelization;* uses OpenMP for parallelization;* generates more than 30 of temporary and output files.* generates more than 30 of temporary and output files.

Problems for porting the application on the grid:Problems for porting the application on the grid:* difficulties in compiling it with OpenMP option;* difficulties in compiling it with OpenMP option;* difficulties in importing the output files (more than 30).* difficulties in importing the output files (more than 30).

Solutions:Solutions:* upgrading and compiling it with gfortran;* upgrading and compiling it with gfortran;* creating a script for compressing the output files in a single * creating a script for compressing the output files in a single

zippzd file before importing it.zippzd file before importing it.


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Jdl fileJdl file

Type = "Job";Type = "Job";JobType = "Normal";JobType = "Normal";Executable = "/bin/sh";Executable = "/bin/sh";Arguments = "job.sh";Arguments = "job.sh";StdOutput = "aq.out";StdOutput = "aq.out";StdError = "aq.err";StdError = "aq.err";InputSandbox = {"aq.exe","job.sh"};InputSandbox = {"aq.exe","job.sh"};OutputSandbox = OutputSandbox = {"aq.out","aq.err","aq.tar.gz"};{"aq.out","aq.err","aq.tar.gz"};


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Script (job.sh file)Script (job.sh file)

chmod 755 aq.exechmod 755 aq.exeecho “Starting the execution..."echo “Starting the execution..."datedate./aq.exe > aq.out./aq.exe > aq.outdatedatetar -cvzf aq.tar.gz *.dattar -cvzf aq.tar.gz *.datecho “End of execution.";echo “End of execution.";


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Results and perspectivesResults and perspectives

Reduction the time of execution:Reduction the time of execution:* run the application in parallel over 24 cores;* run the application in parallel over 24 cores;* the time of execution is reduced almost 24 times.* the time of execution is reduced almost 24 times.

Perspective:Perspective:* running the application over 100 cores.* running the application over 100 cores.

Documents

1 جامعة ابن زهر ~ أكادير IBN ZOHR UNIVERSITY ~ AGADIR CNRST 2011 Rabat June 16, 2011 جامعة التكنولوجيا ~ درسدن UNIVERSITY OF TECHNOLOGY ~ DRESDEN