Browsing by Author "Li, CT"

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Decreasing giant splitting of longitudinal and transverse optical phonons in PbxSr1-xTiO3 due to Pb covalency
(2002-10-14)
Kuo, SY
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Li, CT
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Hsieh, WF
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光電工程學系
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Department of Photonics
In contrast to the increase of giant splitting of longitudinal optical (LO) and transverse optical (TO) phonons in polycrystalline BaxSr1-xTiO3 [Phys. Rev. B. 64, 224103-1 (2001)], a decreasing splitting of the softest A(1)(1TO) and the hardest A(1)(3LO) was observed in PbxSr1-xTiO3. A similar structure but anomalous discrepancies in lattice dynamics of ABO(3) perovskite are related to the diverse electronic states of Pb2+ and Ba2+ ions. In this article, Pb-O interaction is proposed to be more hybridized than Ba-O, and thus the change of effective charge to the LO-TO splitting may be the dominant mechanism in PbxSr1-xTiO3, while unit-cell volume change is in the BaxSr1-xTiO3 systems. (C) 2002 American Institute of Physics.
Lattice dynamics of perovskite PbxCa1-xTiO3
(2004-05-01)
Kuo, SY
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Li, CT
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Hsieh, WF
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光電工程研究所
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Institute of EO Enginerring
Investigation of the structural and vibrational properties of the PbxCa1-xTiO3 (PCT) system exhibits two phase transitions in the range of x=0-1 by using x-ray powder diffraction and Raman spectroscopy. The first transition occurring at xsimilar to0.65 corresponds to the tetragonal-to-cubic phase and the second one occurs near x=0.35 is attributed to the orthorhombic-to-cubic phase. The absence of the intermediate tetragonal phase between orthorhombic and cubic phases (0