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Preparation and Characterization of New Perovskite-like High Dielectric Constant Oxides

Author: LiJian
Tutor: DuYuLei
School: Nanjing University of Technology and Engineering
Course: Materials Science
Keywords: Perovskite High Dielectric Constant Sol-Gel Variable-temperature Raman Spectroscopy Nanorod
CLC: TB34
Type: Master's thesis
Year: 2007
Downloads: 396
Quote: 1
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Abstract


Perovskite high dielectric constant oxides are a kind of functional materials that haswide applications. It has good capability of deposited electricity and uniformed electricfield, so it is applied in the fields of electron, motor and so on. At present, it is also one ofthe pop projects in the microelectric industry. In this dissertation, we choose twoperovskite-like high dielectric constant oxides BaTi2O5 and CaCu3Ti4O12 as the studyobjects. We have successfully prepared the BaTi2O5 and CaCu3Ti4O12 nanopowders bySol-Gel method, and then prepared their nanorods by hydrothermal method and molten saltmethod. The microstructures were investigated in detail. The main work and results are asfollows:1. BaTi2O5 and CaCu3Ti4O12nanopowders were prepared by a wet-chemical method, Sol-Gel method. Their particle diameters are about 50～400nm. However, in thepreparation of CaCu3Ti4O12 nanopowders, there are mostly solid reaction methods inliteratures. In this dissertation, we prepared it by Sol-Gel method. It can reduce thetemperature of calcined 100℃at least. Furthermore, the Sol-Gel method has many merits, such as the high equality, the nicety of chemical measurement, the simple techniques andso on.2. Variable-temperature Raman spectroscopy was used to study the phononcharacteristics and phase transition behaviors of BaTi2O5 and CaCu3Ti4O12 nanopowders.The investigation showed the temperature dependence of the Raman spectra of CCTOnanopowders from 83 to 798K had not been found the phase transition of CCTO. So weconcluded, the sharp reduce of the CCTO’s high dielectric constant under 100K has norelationship to the atom displacement resulted from the reduce of temperature. Accordingto the temperature dependence of the Raman spectra of BaTi2O5, There is a dramaticnarrowing of the Raman lines between room temperature and 83K. Several Raman peaksbreak up to clusters of several sharp peaks. The Raman spectra of BaTi2O5 occurs a seriesof transformations at bout 740K. There is some vibration modes disappeared, whichindicate the change of the structure. The phase transition can be interpreted as theferroelectric phase transition.3. The BaTi2O5 polycrystalline nanorods were successfully prepared by hydrothermal（solvothermal） method. The diameters of the nanorods are about 30～100nm, and 200～ 400nm length. The formation of nanorods is relating to that oleic acid changes to micellerods in 1-octane. And we investigated the good conditions for forming nanorods in thismethod.The CCTO nanorods were successfully prepared by molten salt method. Thediameters of the nanorods are about 50～80nm, and 100～250nm of length. And theformation of the nanorods of CCTO can be interpreted as the Ostwald Ripeningmechanism.

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