Investigation of the dynamic properties of ferroelectric crystals close to phase transitions

Download

index.pdf

Date

2015

Author

Kiracı, Ali

Metadata

Show full item record

Item Usage Stats

206
views

92
downloads

In this thesis we investigated the dynamical properties of some ferroelectric crystals and ceramics under various temperature and pressure conditions close to the phase transitions. In particular, we focused on the Raman frequencies, damping constant and the activation energy of soft modes with the pseudospin-phonon coupling in some ferroelectric crystals exhibiting phase transitions. We predicted the critical behavior of the frequency related to the order parameter (spontaneous polarization) in the ferroelectric and/or paraelectric phases of potassium dihydrogen phosphate (KDP), barium titanate (BaTiO3), lead titanate (PbTiO3), lead zirconate titanate (PZT), strontium zirconate (SrZrO3), cadmium niobate (Cd2Nb2O7) and lithium niobate (LiNbO3). For these predictions, our calculations have been performed by using the mean field theory (MFT). We analyzed the damping constant as a function of temperature and/or pressure for the ferroelectrics studied in this thesis by using the pseudospin-phonon coupled model and the energy fluctuation model. We also calculated the temperature dependence of the relaxation time of BaTiO3, PZT and LiNbO3 using our results of the order parameter and the damping constant described from both models studied here. We also used the Landau phenomenological theory to describe the observed behavior of the dielectric constant (or susceptibility) in the ferroelectric and paraelectric phases of BaTiO3 and in the ferroelectric phase of LiNbO3. As a part of this thesis, we calculated the temperature dependence of the frequency of Raman modes for NaNO2 through the Grüneisen parameter. By analyzing the experimental data from the literature, the observed behavior of those ferroelectric crystals is described on the basis of the models studied here.

Subject Keywords

Ferroelectricity., Dielectrics., Crystals., Polarization (Electricity)., Phase transformations (Statistical physics).

URI

http://etd.lib.metu.edu.tr/upload/12618973/index.pdf
https://hdl.handle.net/11511/24800

Collections

Graduate School of Natural and Applied Sciences, Thesis

Suggestions

OpenMETU
Core

Study of phase transitions in polymorphic liquid crystals Nesrullajev, A; Salihoglu, S; Yurtseven, Hasan Hamit (World Scientific Pub Co Pte Lt, 1998-01-01) This work presents our investigations of mezomorphic properties of two polymorphic liquid crystals, namely, 4-nonyloxy-4-butoxyphenyl benzoate and N-(-4-heptyloxybenzylidene-4-butylaniline) in a wide temperature range, particularly, in the phase transition regions. By means of an original Experimental method. the heterophase regions and also the phase transition temperatures have been determined for these materials with high accuracy. These phase transition intervals have been analyzed using a mean field mo...
Study on the Structural and Electrical Properties of Sequentially Deposited Ag-Ga-In-Te Thin Films Coskun, EMRE; Gullu, H. H.; Parlak, Mehmet; Ercelebi, C. (2015-02-01) The structural properties and electrical conduction mechanisms of Ag-Ga-In-Te thin films deposited by a combination of e-beam and thermal evaporation methods were studied for various annealing temperatures. Structural analysis showed the existence of InTe and InTe binary phases at the early stage of crystallization and monophase of AgGaInTe with the main orientation along (112) direction following the post-annealing at 400 C. The effects of the structural changes on electrical properties and temperature dep...
Investigation of physical properties of quaternary AgGa0.5In0.5Te2 thin films deposited by thermal evaporation Karaagac, H.; Parlak, Mehmet (Elsevier BV, 2010-8) The aim of this study is to understand the structural, optical and photo-electrical properties of the quaternary chalcogenide AgGa 0.5In0.5Te2 thin films deposited onto the glass substrates by thermal evaporation of the single crystalline powder. Energy dispersive X-ray analysis (EDXA) showed remarkable change in atomic percentage of the constituent elements after annealing. The X-ray diffraction (XRD) of the films below the annealing temperature of 300°C indicated the polycrystalline structure with co-exis...
Determination of trapping parameters of thermoluminescent glow peaks of semiconducting Tl2Ga2S3Se crystals IŞIK, MEHMET; YILDIRIM, TACETTİN; Hasanlı, Nızamı (2015-07-01) Thermoluminescence (TL) properties of Tl2Ga2S3Se layered single crystals were researched in the temperature range of 290-770 K. U glow curve exhibited two peaks with maximum temperatures of similar to 373 and 478 K. Curve fitting, initial rise and peak shape methods were used to determine the activation energies of the trapping centers associated with these peaks. Applied methods were in good agreement with the energies of 780 and 950 meV. Capture cross sections and attempt-to-escape frequencies of the trap...
Studies on device properties of an n-AgIn5Se8/p-Si heterojunction diode KALELİ, Murat; Parlak, Mehmet; Ercelebi, C. (2011-10-12) In this study, polycrystalline thin films of ternary AgIn5Se8 compounds with n-type conductivity were deposited on p-type Si substrates from the powder of a Ag3In5Se9 single crystal by a thermal evaporation technique. Transport and photo-transport properties of the In/n-AgIn5Se8/p-Si/Al sandwich structure were investigated by analyzing temperature-dependent dc current-voltage (I-V), and photo-response measurements carried out in the temperature range of 200-360 K. In order to obtain the series resistance (R...

Citation Formats

A. Kiracı, “Investigation of the dynamic properties of ferroelectric crystals close to phase transitions,” Ph.D. - Doctoral Program, Middle East Technical University, 2015.