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Development of Bismuth Layer-structured Oxide Devices with Ferroelectric and Conductive Intergrowth Layers

具有铁电和导电共生层的铋层状结构氧化物器件的开发

基本信息

批准号：
11555163
负责人：
MIYAYAMA Masaru
金额：
$ 6.98万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

For Bismuth layer-structured oxides which is now paid attention as a ferroelectric memory device material, studies were conducted on design for intergrowth-structure ferroelectrics with two kind of perovskite layers and on realization of a layer-strucrured material showing both ferroelectric and conductive properties simultaneously. At first, effects of nonstoichiometry and lattice defects on crystal structure and ferroelectric property were examined. Nonstoichiometry (A-site deficiency in perovskite lattice) in strontium bismuth tantalate was found to give increases in Curie temperature and shift of atom positions, resulting in a large remanent polarization. By doping small amount of V into Bismuth titanate ceramics, remanent polarization increased about 3 times of non-doped material. Obtained remanent polarization was as much as the value calculated from single-crystal value for non-oriented ceramics. For the formation of intergrowth materials, the size matching of two perovskite lattice is necessary. It was found that some intergrowth-structure ferroelectrics show larger remanent polarization than those of component ferroelectrics. Stress induced by stacking different perovskite layers was assumed to be responsible for increases in lattice distortion and atom shift. Trial for making conductive perovskite layers was carried out, and substitution of Mn for Fe in Bi_5Ti_3FeO_<15> was found to be effective for an increase in p-type electronic conductivity more than four orders of magnitude. From X-ray diffraction analysis, an intergrowth-structure material with ferroelectric and conductive perovskite layers was confirmed to be formed though minor second phases are contained in samples. From these results, it was found that a marked improvement of ferroelectric property can be achieved by control of nonstoichiometry and lattice defects, and the guiding principle was obtained for design of intergrowth-structure formation and fusion of different electrical functions.

针对目前备受关注的铁电存储器件材料--铋层状氧化物，开展了两种钙钛矿型共生结构铁电材料的设计和实现同时具有铁电和导电性能的层状结构材料的研究。首先考察了非化学计量比和晶格缺陷对晶体结构和铁电性能的影响。非化学计量比(钙钛矿晶格中的A位缺陷)被发现使钽酸锶铋的居里温度升高，原子位置移动，导致较大的剩余极化。在钛酸铋陶瓷中掺入少量的V，其剩余极化强度比未掺杂的提高了约3倍。对于无取向陶瓷，测得的剩余极化与由单晶值计算得到的值相当。对于共生材料的形成，两个钙钛矿晶格的尺寸匹配是必要的。结果表明，某些共生结构的铁电材料的剩余极化比组元铁电材料的要大。不同的钙钛矿层堆积引起的应力是导致晶格变形和原子移位增加的原因。进行了制备导电钙钛矿层的试验，发现在Bi5Ti3FeO；15&gt；中用Mn替代Fe可以有效地使p型电子电导率提高四个数量级以上。X射线衍射分析表明，虽然样品中含有少量的第二相，但形成了具有铁电和导电钙钛矿层的共生结构材料。结果发现，通过控制非化学计量比和晶格缺陷可以显著改善铁电性能，为不同电功能的共生结构的形成和融合的设计提供了指导原则。