DIELECTRIC PROPERTIES IN ORIENTED THIN FILMS OF TUNGUSTEN-BRONZE-TYPE FERROELECTRIC Ba_6Ti_2Nb_8O_<30>

钨青铜型铁电体Ba_6Ti_2Nb_8O_<30>定向薄膜的介电性能

• 批准号: 12650326
• 负责人: SHIRAFUJI Junji
• 金额: $ 2.05万
• 依托单位: FUKUI UNIVERSITY OF TECHNOLOGY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12650326/
• 关键词: ferroelectric; Ba_6Ti_2Nb_8O_<30>; tungsten-bronze; metalorganic deposition; internal stress; spontaneous polarization; 強誘導体; 変形キュリー・ワイス則

(1) In order to investigate the origin for the extraordinary broad peak in the dielectric constant vs. temperature characteristics in Ba_6Ti_2Nb_8O_<30> ceramics, the temperature dependence of the dielectric constant in oriented thin films grown on (111)Pt/Ti/Si0_2/Si substrates by MOD method. Although the MOD films do not have enough orientation and their phase transition temperature shifts by about 13℃ to a higher temperature in comparison with the case of crystalline materials (245℃), it is observed no broad peak ; this suggests that the dielectric properties of ceramic samples are strongly influenced by internal stresses with random directions.(2) It is confirmed that the films grown on (100)SrTiO_3 and (100)MgO substrates align well along c-axis and that the a-axis of the grown films is tilted by ±18.5° with respect to the a-axis of the substrate. This tilted nature is closely related to the peculiar arrangement of oxygen octahedra in the unit cell of the teragonal tungsten-bronze structure.(3) The polarization-electric field characteristics are measured in the first time in ceramic samples as a function of temperature. It is found that the remanent polarization decreases with increasing temperature and tends to vanishe at 160〜175℃ this temperature is significantly lower than the phase transition temperature of single crystals (245℃) or the peak temperature of the dielectric constant in ceramic samples (180〜200℃). Moreover, the magnitude of the spontaneous polarization is as low as 1μC/cm^2, suggesting that only a small fraction of domains can probably make polarization inversion.(4) A polarized-light optical microscope observation is carried out on 100〜150 μm thick ceramics to check the domain structure along the thickness diraction. It is found that the size and the portions having birefringence are quite small in accordance with the experimental fact of very small spontaneous polarization.

(1)为了研究Ba_6Ti_2Nb_8O_<30>陶瓷介电常数与温度特性中异常宽峰的起源，采用MOD方法在(111)Pt/Ti/SiO_2/Si衬底上生长的取向薄膜介电常数的温度依赖性。虽然MOD薄膜没有足够的取向，并且与晶体材料的情况（245℃）相比，其相变温度移动了约13℃至更高的温度，但没有观察到宽峰；这表明陶瓷样品的介电性能受到随机方向内应力的强烈影响。(2)证实在(100)SrTiO_3和(100)MgO衬底上生长的薄膜沿c轴排列良好,并且生长薄膜的a轴相对于衬底的a轴倾斜±18.5°。这种倾斜性质与四方钨青铜结构晶胞中氧八面体的特殊排列密切相关。(3)首次测量了陶瓷样品中极化电场特性随温度的变化。研究发现，剩余极化随着温度的升高而降低，并在160〜175℃时趋于消失，该温度明显低于单晶的相变温度（245℃）或陶瓷样品介电常数的峰值温度（180〜200℃）。而且，自发极化的幅度低至1μC/cm^2，表明只有一小部分磁畴可能发生极化反转。(4)对100〜150μm厚的陶瓷进行偏光光学显微镜观察，以检查沿厚度方向的磁畴结构。根据非常小的自发极化的实验事实，发现具有双折射的尺寸和部分相当小。

项目成果

Shuji Ohtsubo: "Chemical Solution Deposition of Oriented Ba_6Ti_2Nb_8O_3O Thin Films"Memoirs of Fukui Univ. Technology. No.32(印刷中). (2002)

大坪修二：“取向Ba_6Ti_2Nb_8O_3O薄膜的化学溶液沉积”福井大学回忆录第32期（出版中）。

Shuji Ohtubo: "Dielectric Properties of Tungsten-Bronze-Type Ferroelectric Ba_6Ti_2Nb_8O_<30> ceramics"Memoir Fukui Univ. Technol.. 30. 85-92 (2000)

Shuji Ohtubo：“钨青铜型铁电Ba_6Ti_2Nb_8O_<30>陶瓷的介电性能”回忆录福井大学。

大坪 修司: "タングステンブロンズ型強誘電体Ba_6Ti_2Nb_8O_<30>セラミックスの誘電特性"福井工業大学研究紀要. 30. 85-92 (2000)

大坪修二：“钨青铜铁电Ba_6Ti_2Nb_8O_<30>陶瓷的介电性能”福井工业大学研究通报30. 85-92（2000）。

Shuji Ohtubo: "Chemical Solution Deposition of Oriented Ba_6Ti_2Nb_8O_<30> Thin Films"Memoir of Fukui Univ. Technol.. 32(in print). (2002)

大土保修二：《取向Ba_6Ti_2Nb_8O_<30>薄膜的化学溶液沉积》福井大学回忆录

Shuji Ohtubo: "Chemical Solution Deposition of Oriented Ba_6Ti_2Nb_8O_<30> Thin Films"Memoir Fukui Univ. Technol.. 32 (in press). (2002)

Shuji Ohtubo：“取向Ba_6Ti_2Nb_8O_<30>薄膜的化学溶液沉积”回忆录福井大学。