2006 Fiscal Year Final Research Report Summary
THEORETICAL APPROACH ON PHASE TRANSITION AND PHYSICAL PROPERTIES DUE TO QUANTUM EFFECT IN PEROVSKITE-OXIDES
| Project/Area Number |
15540367
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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 |
Mathematical physics/Fundamental condensed matter physics
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| Research Institution | Gifu University |
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Principal Investigator |
MATSUSHITA Eiko GIFU UNIVERSITY, FACULTY OF ENGINEERING, PROFESSOR, 工学部, 教授 (20183105)
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| Project Period (FY) |
2003 – 2006
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| Keywords | PEROVSKITE-OXIDE / PHASE TRANSITION / QUANTUM EFFECT / PHONON / RELAXOR / HIGH-Tc SUPERCONDUCTOR / PROTON CONDUCTOR |
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| Research Abstract |
In Perovskite-type oxides, several important physical properties are known as anomalous conductivities and the useful applications (for example, Pb-excluded ferroelectrics applied to high capacitance condensers and electrostrictive actuators, quantum paraelectrics with paraelectric (PE)-ferroelectric (FE) transition, and furthermore, high-temperature superconductivity in perovskite-related oxides.) In this research project, we have paid attention to the oxygen octahedron network, and investigated the characteristic phonon properties to the structure with intrinsic quantum effect. The fruitful results were obtained from analytic theoretical approach in the microscopic viewpoint.
The contents are divided under the following four heads.
1. Proton conductivity as the basic mechanism of clean fuel cells
A model of proton conduction was proposed basing on quantum mechanical calculation for H-diffusion on and between temporally made O-H-0 bond, and optimum path was predicted in acceptor-doped pe
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rovskite-oxides. The difference between quantum H-motion and no-quantum Li-diffusion was made clear by changing the network of O-octahedron.
2. Quantum Paraelectricity
By extending soft mode theory for transverse optical phonon, quantum PE-FE transition was explained successfully for applied pressure and oxygen isotope 160-180 substitution in a unified picture. The quantum critical exponent at the transition point was also investigated in a microscopic approach.
3. Relaxor ferroelectricity with morphotropic phase boundary
The definition of relaxor behaviors was proposed to distinguish from glass properties in the microscopic theory for order-disorder type transition. X-ray diffuse scattering and NMR-NQR spectra were discussed, and the conditions for relaxor appearance were presented in perovskite-oxides following displacive-type transition.
4. High-temperature superconductivity
We succeeded to make clear the role of the longitudinal optical phonon in superconductors with high transition temperature Tc. For some types of perovskite-related oxides, 160-180 Isotope effect in Tc was explained successfully in an extended BCS-like equation with real-space representation. The idea of quasi-particle mediated Cooper-pair was also presented. Less
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