| Summary: | 碩士 === 國立臺灣師範大學 === 物理學系在職進修碩士班 === 89 === Abstract
We study the LiNbO3 (Fe — doped) crystals by Infrared absorption spectra and Raman scattering. The samples were Fe-doped with 000ppm, 050ppm, 100ppm, 300ppm, 500ppm and 750ppm.
According to the group theory, There are 27 vibration modes for pureLiNbO3 at zero wave vector, which are divided as 4A1、5A2, and 9E modes (E modes degenerate into 2). Whereas A1 modes and E modes are both Raman and infrared active, A2 modes are Raman and infrared inactive.
In our experiment, the modes of A1 group are found as 250, 275, 331, 633 cm-1 and the modes of E are found as157, 172, 235.5, 321.5, 354.7, 439.3, 578 and 625 cm-1, All these modes corresponding to the group theory.
In our study, different concentrations of iron doped LiNbO3, almost do not have obvious change in the frequencies of the phonon modes. It may be due to the small concentrations of doped iron. In our experiment, when the temperature was lowered to 30K, an impurity mode around 80cm-1 appeared. This is the first report in the infrared study . The frequency of this impurity mode is 81cm-1 for 300ppm iron-doped LiNbO3, 82 cm-1 for 500ppm iron-doped LiNbO3 and 83 cm-1 for 750ppm iron-doped LiNbO3. At 30 K, lines 236.3 cm-1 and 280 cm-1 were clearly separated only in 750 ppm sample.
The mode E-TO5 calculated by by Caciuc et al. 15 is 334 cm-1 and is
419 cm-1 by Parinski et al. 16 was
not found neither in our experiment nor in the literature . According to the literature, the mode 281 was not reported neither by theory nor by experiment reports. We also found E-TO7 shift to 434.5 cm-1 of 100 ppm doped sample, ( for other concentration sample, E-TO7 is around 439 cm-1）
|
|---|
