臺灣博碩士論文加值系統

Bi0.5-xNa0.5-xKxRExTiO3 (稀土元素= La 、Sm 和 Gd) 非鉛陶瓷系統以濃度 x = 0.05, 0.025, 0.0125 和 Bi0.5-xNa0.5-yKyRExTiO3 陶瓷與x = 0.0125, 和 y = 0.09 以傳統陶瓷處理技術成功地製備陶瓷塊材。此陶瓷系統之結構與微觀結構以XRD繞射分析與電子顯微鏡微觀分析觀察，結果發現，Bi0.5-xNa0.5-xKxRExTiO3陶瓷具有rhombohedral相，且非晶質批覆於尖銳的試片表面，顯示於材料系統之中有玻璃相產生。粒徑大小則發現與摻雜之稀土元素不同而改變，且非晶相於試片中產生的量與摻雜量有關。於介電量測中觀察得知，相變化於試片中發生，分別是鐵電轉成反鐵電與鐵轉成順電相，且更廣的波峰顯示更多的擴散相變化，即 稀土元素造成缺陷與區域性的應變場使材料電性改變。由交流阻抗分析得知，非晶相對電性的影響取決頻率與溫度，由Cole-cole plots (Z’-Z”)得知，在不同溫度下皆測得之單半圓，表示材料的均質性與成份分布均勻。鬆弛現象的產生與氧空缺有關。高Gd摻雜量之BNKT陶瓷系統具有教少的非晶相，因此，較少的非晶相產生於晶界，造成電性的改變。並發現Sm摻雜之試片具有較高的殘留極化值(Pr=33.4 µC/cm2)，較低的矯頑電場(Ec=19.8 kV/cm)，因摻雜元素之離子半徑差異小，使電偶極矩較易旋轉。高密度與小晶粒尺寸，影響導電性與機電特性，於Gd摻雜之試片量測中，達到高Kp值與高晶界導電率。

Lead-free material system of Bi0.5-xNa0.5-xKxRExTiO3 (RE = La, Sm and Gd) ceramics with concentration x = 0.05, 0.025, 0.0125 and Bi0.5-xNa0.5-yKyRExTiO3 ceramics with x = 0.0125, and y = 0.09 were successfully synthesized by conventional ceramic processing techniques. The structural and micro structural properties of these ceramics were examined using X-ray diffractometer, and electron microscopy. XRD of Bi0.5-xNa0.5-xKxRExTiO3 ceramics has shown the presence of phases. Amorphous phase coated on granular surfaces and sharp edge of fractured surface specimens indicates the formation of glassy phase in this system. Grain size is found to change with rare earth element. Microstructure indicates the different amount of amorphous phase in different rare earth doped ceramic. The temperature dependence of dielectric measurement reveal that the solid solutions experience two phase transitions from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric. Broadening of peak parameter indicates higher diffuse phase transition implying that rare earth dopants introduce defects and localized strain field and hence modification in electrical properties of material. AC impedance study was carried out to separate the contribution of amorphous phase and the effect of amorphous phase on electrical properties. Impedance is found to be dependent on temperature and frequency. Cole-cole plots (Z’-Z”) show single semicircles at all temperatures indicating the uniform distribution and homogeneity in the specimen under study. Relaxation phenomenon is found to exist due to oxygen vacancies. Grain boundary conductivity is observed to be high in Gd doped BNKT ceramics due to less amorphous phase indicating the effect of amorphous phase existing at the grain boundary on the electrical conductivity. Higher magnitude of remanant polarization (Pr=33.4 µC/cm2) with lower coercive field (Ec=19.8 kV/cm) is observed in Sm doped Bi0.5-xNa0.5-yKyRExTiO3 specimen, due to less difference in ionic radii of host and doped cation which makes easy switching of dipole. Highly dense and smaller grain size has effected on conductivity and electromechanical property to achieve higher value of kp as well as grain boundary conductivity in Gd doped BNKT specimen.

Abstract i
Preface ii
Content iii
List of Figure v
List of Table vii

CHAPTER I
INTRODUCTION 1
1.1 Lead-Free Materials System I-1
1.2 The factor affecting dielectric and piezoelectric properties
of lead containing ferroelectric perovskite I-2
1.3Research Objectives I-4

Chapter II
Experimental Procedures II-1
2.1 Powder preparation II-2
2.2 Material synthesis II-3
2.3 Specimen Characterization II-7
2.3.1 Crystal structure by X-ray diffraction II-7
2.3.2 Density measurement II-7
2.3.3 Scanning electron microscopy (SEM) II-7
2.3.4 Transmission Electron Microscopy (TEM) II-8
2.3.4 Dielectric measurement II-8
2.3.5 Ferroelectric properties (Polarization vs Electric field) II-9
2.3.6 Electromechanical Characterization II-9
2.3.7 AC Impedance spectroscopy II-10





Chapter III
The Effect of La, Sm and Gd on Dielectric and Electromechanical
Properties of BNKT Ceramic III-1
3.1 Phase and Density Analysis III-1
3.2 Microstucture studies III-5
3.3 Dielectric Properties III-9
3.3.1 Temperature Dependence of Dielectric Constant and Loss Tangent III-10
3.4 Ferroelectric property III-20
3.5 Electromechanical property III-24
3.6 Conclusion III-26

Chapter IV
Effect of La, Sm and Gd on Dielectric and Electromechanical Properties of
BNKT ceramics on MPB region IV-1
4.1. Phase and Density IV-1
4.2. Microstructure IV-3
4.3. Dielectric Constant IV-5
4.3.1 Temperature dependence of dielectric constant and loss tangent IV-5
4.4. Ferroelectric property IV-6
4.5. Electromechanical property IV-8
4.6. Cole-Cole plots IV-10
4.7. Conclusions IV-22

Chapter V
General Conclusions V-1

References viii

Appendix xi

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