Ba(B’1/3B”2/3)O3 material property investigation and its application in antenna

• Main Authors: MeiYu Chen, 陳美瑜
• Other Authors: Chih-Ta Chia
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/13667036709736057646

博士 === 國立臺灣師範大學 === 物理學系 === 102 === In this paper, there are two approaches to investigate Ba(B’1/3B”2/3)O3 perovskite ceramics. First study focus on ab-initio simulation of Ba(Mg1/3Ta2/3)O3 and Ba(Mg1/3Nb2/3)O3. The properties of Ba(B’1/3B”2/3)O3 ideal single crystal can be predicted or compared with measured results, such as bulk modulus, normal vibration motions, and permittivity values contributed by phonon and electrons. The other practical study is to design an dielectric resonator antenna of Ba(Mg1/3Ta2/3)O3. The estimated bulk modulus of Ba(Mg1/3Ta2/3)O3 is around 156 (GPa) while measured value is 154 (GPa).The normal vibrational modes of Ba(B’1/3B”2/3)O3, including 9 Raman phonons, 16 IR modes and 3 silent modes, are classified and illustrated in Appendix I. These frequencies of calculated phonon modes are not only quite close to measured frequencies, but also for the permittivity values. The calculated permittivity of Ba(Mg1/3Ta2/3)O3 due to phonon and electron obtained the value of 23.4 and 4.14, respectively; that are consistent with measured value of from IR analysis(εr(phonon)=23.3 and εr(electron)=4.4). The same conclusion also applies for the results of Ba(Mg1/3Nb2/3)O3. In addition, the behaviors of the four dominant modes to permittivity, 2Eu, 2A2u, 4Eu, and 3A2u, were figured out. 2Eu and 2A2u mode are the vibration of Ba atoms against other atoms while 4Eu, and 3A2u mode refer to the relative motion of Ta/Nb atoms and oxygen atoms. Through identifying the actions of each vibration mode, the variation of phonon mode in substituted SrxBa1-x(Mg1/3Ta2/3)O3 system (x< 0.5) can be explained. Two A1g mode (420 cm-1 and 800 cm-1) which have the same vibration atoms perform different behaviors. It indicates that Sr atoms prefer locate on Ba and Mg site, instead Ta site. Furthermore, Sr substituted at Ba site would lead to higher permittivity values because of smaller mass and larger Born effective charge of Sr atoms. The last chapter depicts an attempt to utilize Ba(Mg1/3Ta2/3)O3 ceramics in antenna. The permittivity value was applied in design a dielectric resonator antenna of Ba(Mg1/3Ta2/3)O3 for WLAN applications (2.4 GHz to 2.484 GHz). The measured return loss (S11) have lowest point of -34.67 dB at 2.44 GHz. The efficiency and gain of antenna both peaked at 2.44GHz, being 68 % and 5.13, respectively. Radiation patterns in x-y plane perform omni-directional but the y-z and x-z plane of radiation patterns illustrate the directional radiation.