2003 Fiscal Year Final Research Report Summary
Piezoelectricity and hetero-structure fluctuations in ferroelectric materials having composition near a morphotropic phase boundary
| Project/Area Number |
13650726
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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 |
Physical properties of metals
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| Research Institution | Waseda University |
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Principal Investigator |
KOYAMA Yasumasa Waseda University, School of Science and Engineering, Professor, 理工学部, 教授 (20150295)
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| Project Period (FY) |
2001 – 2003
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| Keywords | PZT / Morphotropic phase boundary / Monoclinic phase / Ferroelectric / ferrielectric / Incommensurate phase |
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| Research Abstract |
In Pb(Zr_<1-x>Ti_x)O_3 (PZT), there exist the ferroelectric tetragonal/monoclinic and monoclinic/rhombohedral phase boundaries around x=0.50, where the very high piezoelectric response has been reported. Among these two boundaries, the former is characterized by the nearly vertical boundary called the morphotropic phase boundary (MPB). In order to understand the physical origin of the excellent piezoelectric property found near the MPB, we have investigated the crystallographic features of the PZT samples around x=0.50 mainly by transmission electron microscopy.
The preliminary examination by means of X-ray powder diffraction revealed that the x=0.50 and 0.48 sample exhibited the tetragonal to monoclinic transition, while in the x=0.46 sample near the monoclinic/rhombohedral boundary the rhombohedral phase was basically found in the temperature range below room temperature. Based on the preliminary data, the details of the crystallographic features of these samples were examined by in-s
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itu observation using a transmission electron microscope. The observation indicated that in the tetragonal to monoclinic transition the monoclinic regions with a lenticular shape were nucleated at the {110} twin boundary in the tetragonal phase. The characteristic features are that the nucleated regions do not basically exhibit the growth process, and that the transition proceeds by the repeated nucleation of the monoclinic regions. The monoclinic phase after the transition is then characterized by the aggregation of the lenticular domains. In the x=0.48 sample, on the other hand, there is no crystallographic domain structure. Only the tweed-type structure was observed in the whole area of the sample. This suggests that the x=0.46 sample consists of nm-sized regions with the monoclinic symmetry. In other words the rhombohedral symmetry indicating by X-ray diffraction is just on average area. The excellent piezoelectric property is thus understood be directly associated with the tweed-type microstructure consisted of the nm-size monoclinic regions. Less
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