| Project/Area Number |
02302021
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| Research Category |
Grant-in-Aid for Co-operative Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体物性
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| Research Institution | (Faculty of Science) Hokkaido University |
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Principal Investigator |
TOKUNAGA Masaharu Hokkaido University, Faculty of Science, Department of Physics Professor, 理学部, 教授 (60001682)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAMURA Eiji Hiroshima University, Faculty of Science, Department of Materials Science, Profe, 理学部, 教授 (00000787)
IKEDA Susumu National Laboratory for High Energy Physics, Associate Professor, 助教授 (80132679)
NODA Yukio Chiba University, Faculty of Science, Department of Physics, Associate Professor, 理学部, 助教授 (80127274)
TOMINAGA Yasunori Ochanomizu University, Faculty of Science, Department of Physics, Professor, 理学部, 教授 (00013540)
YAGI Toshirou Hokkaido University, Research Institute of Electronic Science, Professor, 電子科学研究所, 教授 (30002132)
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| Project Period (FY) |
1990 – 1992
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| Keywords | Hydrogen-bond / Tunneling / Isotope Effect / Neutron Scattering, / Raman Scattering / Structural Phase Transition / Ferroelectric / Order-disorder Transition / High Pressure |
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| Research Abstract |
(1) A long controversy had been held between the proton tunneling model (traditional) and the H_2PO_4 order-disorder model (the new viewpoint presented by us) with respect to the dynamical mechanism of structural phase transition in KH_2PO_4, which is a representative of hydrogen-bonded crystals. The existence of tunneling motions of protons has been proved to be excluded by the experimental results of incoherent neutron scattering.
(2) The Raman spectra of KH_2PO_4 observed and interpreted by Kaminow-Damen and Peercy had been long regarded as the evidence of the former model. New precise experimental data in Raman scattering, hyper-Raman scattering, and far infrared reflection have been obtained on KH_2PO_4, KD_2PO_4 and their isomorphous crystals in wide temperature region and under high pressure. These data have been successfully analysed in terms of the critical relaxation mode and the lowering of the local symmetry of PO_4 radicals due to the disordered structure above the transition temperature.
From both results, the new viewpoint has been concluded to hold as far as KH_2PO_4 type crystals are concerned. This viewpoint will be extended to all hydrogen-bonded crystals.
(3) Phase transitions in zero-dimensional hydrogen-bonded systems M_3H(XO_4)_2 (M=K, Rb, Cs ; X= S, Se) have been found and studied by crystallographical, calorimentrical and optical methods. The origin of the large isotope effect due to the substitution of H by D has been attributed to the difference in geometrical configurations of atoms in the H(XO_4)_2 radical including that of electron densityon the hydrogen bond.
(4) Several new phases and variations of transition temperatures have been found by subsituting H by D and under high pressure in some hydrogen-bonded crystals.
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