2007 Fiscal Year Final Research Report Summary
Theoretical study for anharmonicity in the phonon spectra for a distorted perovskite crystal structure in the photo exitted states
| Project/Area Number |
17540303
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics I
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| Research Institution | Kushiro National College of Technology |
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Principal Investigator |
SUDA Jun Kushiro National College of Technology, Department of Electric engineering, Professor (20369903)
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| Co-Investigator(Kenkyū-buntansha) |
KAMISHIMA Osamu Tohoku University, Institute of Multidisciplinary Research for Advanced Materials, Assistant Professor (90321984)
KAWAMURA Junichi Tohoku University, Institute of Multidisciplinary Research for Advanced Materials, Professor (50142683)
HATTORI Takeshi Tokyo University of Science, Department of Physics, Professor (20029234)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Phonon / Lattice Dynamics / Raman Spectroscopy / Perovskite / Lattice vibration / Anharmonicity |
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| Research Abstract |
In this project the observed temperature dependence of the optirahactive spectra for a distorted perovskite crystal structure (AGaO_3 (A=Nd, La)) in the photo-exited states is examined in terms of phonon-dispersion relations based on the first-principles calculations. We also clarify the origin of anharmonic effects on the linewidth of several rotational modes (e.g, librational mode) using these calculations. For IR spectra in NdGaO_3 the B_<2u>, mode at 174-cm-^<-1> involves mixed vibrations of the Nd atoms and the GaOG octahedra, and the higher frequency mode do not involve motion of Nd atoms above 300-cm-^<-1>. We found that the linewidth of the B_<2u>, mode (174-cm-^<-1>) varied with increasing temperature by comparison with other phonon peaks (356-cm-^<-1>and 595-cm-^<-1>). For the LaGaO_3 temperature dependence of the linewidth for some rotational modes [the Ag (57-cm-^<-1>) and the B_<2g> (118-cm-^<-1> for the low-temperature phase (LT), and the.E_g (52-cm-^<-1>) for the high-temperature phase (HT)] is dominated by the scattering of a thermal phonon by the observed phonon, while that for the bending mode [the E_g (160-cm-^<-1>) for the HT] is dominated by both the scattering and the decay of the observed phonons into two phonons having lower energies. We also have investigated Raman spectra in the LT of LaA1O_3.by similar approach as that in LaGaO_3 We found that this originates in the large frequency gap (band-gap-anharmonic effects) in the DOS that produces a difference in anharmonic effects on each peaks channels in the HT of LaGaO_3 and the LT of LaA1O_3, respectively. In order to examine validlY for this band-gap-ahnarmonic effects on other crystal with lattice dymamical calculation, we have investigated sheelite type crystals. We found that anharmonicity in the Agmodes was explained by a large band-gap-ahnarmonic effects in CaWO_4.
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[Presentation] Phonon images in CaWO_42007
Author(s)
早坂 恭平
Organizer
The 12th International Conference on Phonon Scattering in Condensed Matter, IOP(Institute of Physics)
Place of Presentation
Conservatoire National des Arts et Metiers(CNAM)(パリ)
Year and Date
2007-07-19
Description
「研究成果報告書概要(和文)」より
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