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Studies of ferroelectrics films using micro-Raman spectroscopy and photoluminescence measurements

Posted on:2010-06-18Degree:Ph.DType:Thesis
University:Hong Kong Polytechnic University (Hong Kong)Candidate:Yao, YingbangFull Text:PDF
GTID:2441390002974925Subject:Engineering
Abstract/Summary:
Ferroelectric materials have attracted considerable interests from perspectives of nonvolatile memories, piezoelectric sensors/actuators, infrared detectors and optoelectronic devices etc., due to their unique electrical and optical properties. Three kinds of ferroelectric materials were selected in this thesis: (1) SrxBa1-xNb2O6 (SBN) which possesses tetragonal tungsten bronze (TTB) structure and have been be used as pyroelectric infrared detectors, electro-optics and photorefractive devices; (2) BiFeO3 (BFO), one of the well-known multiferroics, exhibits coexistence of ferroelectric and antiferromagnetic ordering above room temperature and has attracted great attention due to its potentials for novel devices as well as material for fundamental physics investigation; and (3) K 0.5Na0.5NbO3 (KNN), one of the most promising lead-free alternatives to Pb(ZrxTi1-x)O3(PZT)-based compositions due to its high piezoelectric coefficient.;Rare-earth (from La3+ to Yb3+), alkaline earth (Ca2+), and alkali elements (Na+, K +) modified SBN ceramics were prepared and investigated to assess their potential for pyroelectric applications. Temperature dependent (30°C--400°C) unpolarized micro-Raman spectroscopy and low-temperature (12K) photoluminescence (PL) measurements were carried out to study the stress states, ferroelectric phase transitions, and energy structures of the corresponding thin films.;Pure and rare-earth (Sm3+, Eu3+, Gd 3+, and Dy3+)-doped BFO thin films were expitaxially grown on STO(001) and conductive Nb-doped STO(001) (NSTO) single crystal substrates by PLD method. The films were studied by PL and micro-Raman spectroscopies.;Lead-free piezoelectric (K0.5Na0.5)0.96Li 0.04(Nb0.8Ta0.2)O3 thin films were prepared by PLD method on MgO (001) and conductive NSTO (001) single crystal substrates. The phase transitions of the film were studied by temperature-dependent micro-Raman spectroscopy.;SBN-based composite thin films of SBN+BaxSr1-xTiO 3 and SBN+LiTaO3 were prepared in order to study the effects of B-site dopants on the bandgap energies, phase transitions and dielectric properties of the doped SBN thin films. BFO-based composite (SBN+BFO) and multilayered (KNSBN+BFO) thin films were also fabricated by PLD method. They were characterized by ferroelectric and magnetic properties measurements, UV-Vis transmittance measurements, temperature dependent Raman spectroscopy and PL studies. All these composite/multilayered films were shown to be of great interest and value to the materials community.
Keywords/Search Tags:Films, Ferroelectric, Micro-raman spectroscopy, PLD method, Materials, SBN, Measurements, BFO
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