액상 초음파 도핑을 이용한 극미량 La 도핑 BaTiO3 세라믹스의 결함 보상 거동과 전기적 특성 연구

다국어 초록 (Multilingual Abstract)

Barium titanate （BaTiO3） is a key dielectric material used in multilayer ceramic capacitors （MLCCs）. To achieve higher capacitance and improved reliability, precise control of not only the composition and microstructure but also the defect chemistry is essential. The defect chemistry of BaTiO3 is highly sensitive to trace amounts of dopants and impurities, and the resulting charge-compensation behavior plays a critical role in determining its structural, dielectric, ferroelectric, and electrical properties. Nominally undoped BaTiO3 raw materials inevitably contain background impurities at concentrations of approximately 50-100 ppm, which are introduced during raw-material synthesis. These impurities predominantly act as acceptors and are charge-compensated by the formation of oxygen vacancies. They are therefore commonly referred to as universal acceptors and have long been considered a key parameter governing the dominant charge-compensation mechanism during donor doping. According to defect-chemical considerations, donor dopants introduced below this critical concentration are preferentially consumed in compensating the pre-existing acceptors and reducing the associated oxygen-vacancy concentration. Once the donor concentration exceeds this threshold, the dominant compensation mechanism is expected to transition toward more complex defect-compensation behavior involving the formation of cation vacancies and accompanying microstructural changes. Despite its conceptual importance, however, defect-chemical behavior near the universal-acceptor concentration has remained largely inferential rather than being directly verified experimentally. Conventional ball-milling processes, which are widely employed in both industrial and academic research, inevitably introduce external contamination, particularly Zr, through mechanical friction with zirconia milling media. They also suffer from non-uniform dispersion of solid-phase dopants. Consequently, in the trace-doping regime below 100 ppm, it is extremely difficult to distinguish the intrinsic effects of the intended dopant from those arising from dopant inhomogeneity and extrinsic contamination. As a result, defect-chemical studies associated with universal acceptors have remained limited. A more advanced processing technique capable of fundamentally eliminating external contamination while ensuring homogeneous dopant dispersion is therefore required to clearly elucidate the intrinsic defect behavior of BaTiO3. In this study, a liquid-phase ultrasonic doping process was employed to overcome the limitations of conventional processing and to successfully fabricate single-phase BaTiO3 ceramics with homogeneously distributed La3+ ions precisely controlled over the trace concentration range of 0-500 ppm, without milling-derived contamination. The structural, dielectric, ferroelectric, and high-temperature electrical transport properties of the resulting ceramics were systematically investigated. Cross-validation of these independent property measurements demonstrated the effectiveness of the proposed process for trace-level doping control. More importantly, the results experimentally revealed that the universal-acceptor concentration in BaTiO3, which has long been treated primarily as a theoretically inferred parameter, represents an experimentally identifiable compositional boundary near 100 ppm at which distinct changes in defect-compensation behavior and the associated material properties occur. Keywords : MLCC, BaTiO3, defect compensation, universal acceptor, liquid-phase ultrasonic doping.

목차 (Table of Contents)

• 제 1 장 서론 1
• 제 2 장 이론적 배경 4
• 2.1. 적층 세라믹 커패시터(Multi-layer ceramic capacitor) 4
• 2.2. 유전체 (Dielectric materials) 8
• 2.3. 강유전체 (Ferroelectric materials) 12
• 2.4. 티탄산바륨 (BaTiO3) 17
• 2.5. 결함 보상 (Defect compensation) 21
• 2.5.1. 보편적 억셉터 (Universal acceptor) 23
• 2.6. 액상 초음파 도핑 (Liquid-phase ultrasonic doping) 24
• 2.6.1. 액상 도펀트 (Liquid-phase dopant) 25
• 2.6.2. 초음파 혼합 공정 (Ultrasonic mixing process) 27
• 2.7. 임피던스 분광법 (Impedance spectroscopy) 30
• 제 3 장 실험방법 및 특성평가 37
• 3.1. 실험방법 37
• 3.1.1. 분말 혼합 37
• 3.1.2. La-doped BaTiO3 세라믹 소결체 제작 39
• 3.2. 특성평가 40
• 3.2.1. 결정구조 분석 (XRD) 40
• 3.2.2. 소결체 미세구조 분석 41
• 3.2.3. 소결체 유전 특성 분석 41
• 3.2.4. 소결체 강유전 특성 분석 42
• 3.2.5. 소결체 임피던스 분광 분석 42
• 제 4 장 실험결과 및 고찰 43
• 4.1. 구조적 특성 43
• 4.1.1. 결정구조 분석 43
• 4.1.2. 미세구조 분석 48
• 4.2. 유전 특성 50
• 4.3. 강유전 특성 55
• 4.4. 전기적 특성 60
• 제 5 장 결론 68
• 참고문헌 70
• 국문 요약 84