Ferroelectric materials with interfaces : first principles calculations

Ferroelectric materials are characterized by a reversible spontaneous electric polarization in the absence of an electric field. This polarization arises from a non-centrosymmetric arrangement of the ions in the unit cell that produces an electric dipole moment. Ferroelectric materials have been extensively studied in recent years because of their promising properties for a wide range of applications, ranging from three-dimensional trenched capacitors for dynamic random access memories and ultrafast switching to cheap room-temperature magnetic-field detectors, piezoelectric nanotubes for microfluidic systems and electrocaloric coolers for computers. Experimental studies have shown that defects, stacking faults and domain boundaries play an important role in ferroelectric materials. In this thesis the polarization of thin films of the perovskite ATiO3 compounds PbTiO3 and BaTiO3 is investigated. The investigations take advantage of the density functional theory (DFT), a modern theory which permits the treatment of the many electrons problem in real solids. The actual calculations are carried out with the full-potential linearized augmented planewave method (FLAPW) method as implemented in the Jülich DFT code (FLEUR). The applicability of different exchange-correlation potentials is studied. Both AO-terminated and TiO2-terminated surfaces with the polarization in the film plane and perpendicular to the surface are considered. The influence of the surface and stacking faults on the polarization near to the surface have been studied. Without an electric field that compensates the depolarization field a polarization perpendicular to the surface is not stable, but I can stabilize an out-of-plane polarization with different types of defects at the surface. Two different types of domain walls, transversal and longitudinal, in PbTiO3 are considered. I simulated [110]-oriented 180° transversal domain boundaries and [100]-oriented 180° longitudinal domain walls. The latter type of walls is not stable in a stoichiometric material. When such domain walls with bulk polarization are formed, the electric charges accumulated at the interface make the domain walls metallic and unfavorable due to electrostatic energy. I stabilized the longitudinal domain walls by creating defects on the interface. The lateral extension of these domain walls is studied and compared to experimental results.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2011

Author dc:creator

• Rahmanizadeh, Kourosh

Contributors dc:contributor

• Blügel, Stefan

• info:eu-repo/classification/ddc/530
• Dichtefunktionalformalismus
• Elektrische Polarisation
• Gitterbaufehler
• Physik
• ferroelektrische Materialien
• dünne Filme
• Domänenwände
• ferroelectric materials
• stacking faults
• domain walls

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-114529%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A52294