2006 Fiscal Year Final Research Report Summary
Ferroelectric microregion and photo-induced superparaelectricity
| Project/Area Number |
17540289
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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 | University of Tsukuba |
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Principal Investigator |
UWE Hiromoto University of Tsukuba, Prof.Emeritus (10132979)
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| Co-Investigator(Kenkyū-buntansha) |
MINAMI Hidetoshi University of Tsukuba, Inst.of Material Science, Lecturer (00190702)
OKA Kunihiko 産業技術総合研究所, National Institute of Advanced Industrial Science and Technology, Principal Researcher (10356678)
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| Project Period (FY) |
2005 – 2006
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| Keywords | quantum paraelectrics / electron phonon interaction / photoconductivity / streaming conduction / ferroelectric soft phonon / foatinz zone method |
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| Research Abstract |
Magnetoresistance mobility has been measured by means of pulse photoconductivity measurements in KTaO_3 and SrTiO_3 at the temperature range below 100K. The employed method of the photoconductivity measurement for materials with high dielectric constant is based on an idea that we use both edges of several millimeters of the sample itself as blocking electrodes. Temperature variation of the magnetoresistance mobility coincides with the previous measured Hall mobility. For the measurements using long-wavelength light to excite electrons within a crystal, nonlinear conduction is observed above a moderately low electric field. For SrTiO_3, the streaming conduction is observed, in which drift mobility of electrons saturates with increasing field. The kinetic energy of the streaming electron is found to coincide with the energy of the ferroelectric soft phonon. For the stress induced ferroelectric phase transition, we also find the streaming motion of photo-induced carriers, in which kineti
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c energy of the streaming electron coincides with the energy of the ferroelectric soft phonon Eu to vanish at the ferroelectric transition. For KTaO_3, the saturation phenomenon of the drift mobility is not observed. Although belong to the same category of the quantum ferroelectric, electron-phonon interaction with ferroelectric soft phonon differs between them and the strength is bigger for SrTiO_3 than for KTaO_3. This seems to correspond to the fact that doped SrTiO_3 is superconductive at low temperatures but doped KTaO_3 is not. For the measurement with short-wave length light to investigate conduction in surface region in SrTiO_3, the magnetoresistance mobility is found to exhibit anomalies at temperatures of previous reported unusual behavior. We have also tried to prepare single crystals of SrTiO_3 with a good quality by the floating zone (FZ) method. When comparing with commercial crystals by the Bernouilli method, our FZ crystals with are found to have smaller etch-pit density and almost equal internal strains. However, the magnetoresistance mobility is found to be smaller than for crystals by the Bernouilli method. The Sr defect number for the FZ crystal seems to be larger than for Bernouilli crystals, which leads to the high scattering of photo carriers in FZ crystals Less
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Research Products
(2 results)
