微波介電材料MgTiO3-CaNdTiO3系統
Abstract
微波介電材料CaTiO3具有極高的介電常數，非常符合現代微波被動元件小型化的需求，但其缺點為過高的共振頻率溫度係數 。我們摻雜 為負值的MgTiO3，組合成 趨近於0的複合物，本論文的主旨是探究MgTiO3- CaNdTiO3系統之光譜性質。
我們測量(1-x)MgTiO3-xCa0.61Nd0.26TiO3+Mn2O3 (x = 0.2、0.4、0.6、0.8)樣品的拉曼散射光譜，715 cm-1拉曼散射峰屬於氧八面體呼吸振動模，其強度隨x增加而變小，並與微波頻段之Q × f值的變化趨勢一致。此外，Ca1-yNd2y/3TiO3+Mn2O3 (y = 0.3、0.39、0.48)樣品的524 cm-1氧八面體扭轉振動模的半高寬與Q × f值呈現反比關係，這些實驗結果意味著，氧八面體的振動與樣品的介電特性有緊密關聯性。
我們測量上述樣品的紅外光反射光譜，發現紅外光活性振動模中，氧八面體相對於B site陽離子彎曲振動模為樣品介電常數的主要貢獻者，且其所占介電損失的比例也最大。此振動模的對稱性低，具有較大之極化能力，亦即離子轉動的程度較大，因此產生更大的阻尼所導致。
CaTiO3-based ceramics are attractive candidates for use as miniaturization of microwave devices. It exhibits a high permittivity accompanied however by a large positive value. In contrast, MgTiO3 possesses negative values. Thus, potentially useful ceramics can be obtained by forming solid solutions between CaTiO3 and MgTiO3. In this thesis, we study the optical properties of MgTiO3- CaNdTiO3 systems. (1-x)MgTiO3 - xCa0.61Nd0.26TiO3 + Mn2O3 (x = 0.2, 0.4, 0.6, and 0.8) were studied by Raman-scattering spectroscopy. A Raman-active phonon mode observed near 715 cm-1 can be assigned to the stretching breath of oxygen octahedron. The intensity of this phonon decreses with increasing x and follows the trend of variation of the Q × f value measured in microwave frequency region. Additionally, the changes in linewidth of a Raman peak at about 524 cm-1 (torsional vibrations of oxygen octahedron) observed in Ca1-yNd2y/3TiO3 + Mn2O3 (y = 0.3, 0.39, and 0.48) are inversely proportional to the Q × f value. These results highlight the vibrations of oxygen octahedron are strongly correlated with the microwave properties of MgTiO3- CaNdTiO3 systems. Finally, the analysis of infrared reflectance spectra of MgTiO3- CaNdTiO3 systems shows that the bending mode of the oxygen octahedron contributes largely the dielectric constant and a concomitant high dielectric loss.
CaTiO3-based ceramics are attractive candidates for use as miniaturization of microwave devices. It exhibits a high permittivity accompanied however by a large positive value. In contrast, MgTiO3 possesses negative values. Thus, potentially useful ceramics can be obtained by forming solid solutions between CaTiO3 and MgTiO3. In this thesis, we study the optical properties of MgTiO3- CaNdTiO3 systems. (1-x)MgTiO3 - xCa0.61Nd0.26TiO3 + Mn2O3 (x = 0.2, 0.4, 0.6, and 0.8) were studied by Raman-scattering spectroscopy. A Raman-active phonon mode observed near 715 cm-1 can be assigned to the stretching breath of oxygen octahedron. The intensity of this phonon decreses with increasing x and follows the trend of variation of the Q × f value measured in microwave frequency region. Additionally, the changes in linewidth of a Raman peak at about 524 cm-1 (torsional vibrations of oxygen octahedron) observed in Ca1-yNd2y/3TiO3 + Mn2O3 (y = 0.3, 0.39, and 0.48) are inversely proportional to the Q × f value. These results highlight the vibrations of oxygen octahedron are strongly correlated with the microwave properties of MgTiO3- CaNdTiO3 systems. Finally, the analysis of infrared reflectance spectra of MgTiO3- CaNdTiO3 systems shows that the bending mode of the oxygen octahedron contributes largely the dielectric constant and a concomitant high dielectric loss.
Description
Keywords
陶瓷, 微波, 光譜, ceramics, microwave, optical properties