La2O3 첨가에 따른 BaTiO3의 미세구조 및 유전특성
Microstructure and dielectric properties in the La2O3-doped BaTiO3 s ystem
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La2O3 첨가량에 따른 결정상 및 미세구조 변화와 유전특성과의 상관관계에 대해 연구하였다. 고상반응법을 이용해 합성된 0.3mol% TiO2 과잉 BaTiO3 분말에 대해 La2O3 첨가량을 다르게 첨가하여 1250°C에서 2시간 동안 소결되었다. 상온에서 측정된 XRD는 La2O3 첨가량이 증가함에 따라 lattice parameter가 변화하였고, 정방정비가 감소하였다. 이는 La3+가 Ba2+자리에 치환되어 정방정상의 불안정성을 높여 입방정상으로 상전이 된 것으로 설명할 수 있다. La2O3 첨가량이 증가할 때, 임계입자성장구동력(Δgc)이 최대 입자성장구동력 (Δgmax)보다 높아져, 입자크기와 밀도가 감소하였다. 유전상수는La2O3가 증가함에 따라 감소하였는데, 이를 결정상 및 미세구조의 변화에 대한 효과로 분석하였다.
Abstract
The effect of La2O3 addition on the crystalline phase, microstructure, and dielectric properties of BaTiO3 has been studied as a function of the amounts of La2O3. 0.3 mol% TiO2-excess BaTiO3 powder was synthesized by solid-state reaction, and then the powder compacts with various amounts of La2O3 were sintered at 1250°C for 2 hours. Room temperature XRD showed changes in the lattice parameters and a decrease of tetragonality (c/a) as the amounts of La2O3 increased. It can be explained that the phase transition from tetragonal to cubic phase occurred because La3+ replaced Ba2+ site, which increased the instability of the tetragonal phase. As La2O3 was added over 0.1 mol%, the critical driving force for growth(Δgc) increased over maximum driving force (Δgmax). As the result, the grain size decreased with La2O3 addition. Dielectric constant decreased as the amounts of La2O3 increased, which was analyzed with crystal structure and microstructure.
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