1988 Fiscal Year Final Research Report Summary
A Unified Theory on the Ferroelectric Phase Transition in Analogy with the Moriya Theory on Itinerant Electron Weak Ferromagnets
| Project/Area Number |
62540255
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
物性一般（含極低温･固体物性に対する理論）
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| Research Institution | Hokkaido University |
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Principal Investigator |
TOKUNAGA Masaharu Hokkaido University Fac. of Science, 理学部, 教授 (60001682)
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| Project Period (FY) |
1987 – 1988
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| Keywords | Ferroelectric Phase Transition / Soft Phonon / 量子常誘電性 / ソフトフォノン |
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| Research Abstract |
A unified theory has been constructed on the ferroelectric phase transition by making use of the analogy between the Moriya theory on itinerant electron weak ferromagnets and the selfconsistent phonon theory in ferroelectrics. The following conclusions have been obtained.
1. The paraelectric monent P_c is evaluated from the Curie constant fo each substance. The ratio P_c to the saturation moment P_s plays an essential role to discuss the transition mechanism of the substance concerned. This ratio deviates from
1. in displacive type ferroelectrics. The parameter 1/t_0 is defined to denote the decreasing rate of an harmonic oscillator in frequency with the decreasing rate in mean square amplitude. The above deviation is explained by the existence of t_0.
2. The ratio D of the electrostatic dipole-dipole interaction to the total interaction has been taken into account in computing the dielectric susceptibility. The effect of t_0 in 1 is emphasized in this case more than in the case of no D.
3. In some ferroelectrics, the decrease in soft mode frequency and the increase in dielectric susceptibility saturate near T=0 without the transition into the ferroelectric phase. This phenomena is explained as the suppresion of the decrease in frequency by the zero point vibration, and called 'quantum paraelectricicty'. A parameter R is introduced to describe this phenomena so as to derive the results in 1 and 2 in the classical limit h-0, and to separate the effect of t_0. The effect of D releases the suppression due to the quantum effect.
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