비납계 압전체 세라믹스 (1-x)(Na_(0.5)K_(0.5))NbO₃-xLiNbO₃(NKN-LN)의 유전특성에 관한 연구

Abstract

Potassium sodium niobate (Na0.5K0.5NbO3 ; NKN) is one of lead-free piezoelectric materials. However, the NKN ceramic is difficult to obtain by ordinary sintering method due to high sintering temperature above 1400 ℃. To improve the electrical properties, BaTiO₃, SrTiO₃, LiNbO₃ and LiTaO₃ is added in NKN compositions. To improve the dielectric and piezoelectric properties, NKN ceramics with the addition of LiNbO₃, (1-x)(Na0.5K0.5)NbO₃ - x(LiNbO₃) (x = 0.1 ~ 0.4) have been synthesized by solid-state reaction method. Crystal structure and surface morphology are confirmed by the X-ray diffraction and SEM measurements, respectively. The temperature and frequency dependence of dielectric, piezoelectric, ferroelectric properties were investigated by dielectric constant, electromechanical coupling factor (kp). and P-E hysteresis loop measurements, respectvely. At the boundary of x = 0.3, the crystal phase is changed. For small addition for x ≤ 0.3, the phase transition temperature is lower and piezoelectric properties is enhanced, well saturated P-E hysteresis loop is obtained. For x > 0.3, multi-phases with NKN, K3Li2Nb5O15(KLN) and LiNbO₃ were obtained. In this work. the dielectric, piezoelectric, ferroelectric properties are investigated for the additions of LiNbO₃ composition.