2004 Fiscal Year Final Research Report Summary
Design for Lead-free Ferroelectric Functional Materials using Layered Crystal Lattices
| Project/Area Number |
14205096
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Inorganic materials/Physical properties
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| Research Institution | The University of Tokyo |
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Principal Investigator |
MIYAYAMA Masaru The University of Tokyo, Research Center for Advanced Science and Technology, Professor, 先端科学技術研究センター, 教授 (20134497)
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| Co-Investigator(Kenkyū-buntansha) |
NOGUCHI Yuji The University of Tokyo, Research Center for Advanced Science and Technology, Lecturer, 先端科学技術研究センター, 講師 (60293255)
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| Project Period (FY) |
2002 – 2004
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| Keywords | Bisumuth layer-structured ferroelectrics / Lattice defects / Oxygen vacancies / Oxide ion conduction / Domain structure / Intergrowth structure / Piezoelectric force microscopy / ab initio calculation |
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| Research Abstract |
Materials Design to realize novel ferroelectric and integrated functions was conducted using layered crystal lattices of Lead-free bismuth layer-structured oxides, and following results were obtained.
1.Improvement of ferroelectric properties by defect engineering
A large permanent polarization of 28μC/cm^2 was confirmed in strontium bismuth tantalite single crystals with Sr deficiency and excess Bi. This was attributed to vacancies at the Sr sites leading to an increase in lattice distortion. Soft to hard polarization properties were realized by controlled doping of Rare-earth elements. Very large permanent polarizations were observed in bismuth titanate single crystals doped with higher-valent ions as W and Nb. This was attributed to decreases in oxygen vacancies and leakage current. The estimated vacancy-formation energies suggested that the doping results in a decrease of defect concentration and stabilization of the perovskite layers.
2.Formation of intergrowth layered-structures and evaluation
The intergrowth superlattice of bismuth titanate and barium bismuth titanate showed a remanent polarization of 52μC/cm^2, which is the highest in Lead-free perovskite materials.
3.Creation of integrated functions
The Mn-substituted bismuth titanate single crystal showed semiconductivity along a-axis, and a memory-effect of the semiconductivity due to changes in polarized state was discovered. This effect was also confirmed in Lead-containing ferroelectrics, and thus expected for applications to new functional devices.
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