用传统固相反应法制备了(K0.5Na0.5)NbO3(KNN)和0.98(K0.5Na0.5)NbO3-0.02LaFeO3(0.98KNN-0.02LF)无铅陶瓷, 并对其介电、铁电性质以及相结构进行了研究. KNN陶瓷是正交相, 0.98KNN-0.02LF陶瓷是伪立方相结构. 介电研究表明: 0.98KNN-0.02LF 陶瓷的介温曲线与KNN陶瓷相比较出现两点异常: (i)正交相–四方相相变温度(TO-T)和四方 相–立方相相变温度(TT-C)均降低; (ii)最高介电常数温度Tm附近的相变温度宽化. 并且, 0.98KNN-0.02LF陶瓷在0~400℃内显示了相对比较平坦的介电常数, 介电常数达到2000, 介电损耗低于4%. 电滞回线变“窄”进一步证明了0.98KNN-0.02LF陶瓷的弛豫性.
Pure (K0.5Na0.5)NbO3 and 0.98(K0.5Na0.5)NbO3-0.02LaFeO3 ceramics (abbreviated as KNN and 0.98KNN-0.02LF, respectively) were prepared by a solid state reaction approach, and their crystal structure, dielectric and ferroelectric properties were investigated. Pure KNN and 0.98KNN-0.02LF ceramics are the orthorhombic structure and pseudo-cubic perovskite structure, respectively. Dielectric measurements revealed that the dielectric permittivity curves of 0.98KNN-0.02LF ceramics present two anomalies compared with pure KNN: (i) The orthorhombic- tetragonal transition (TO-T) and the tetragonal-cubic transition (TT-C) shifts to lower temperatures. (ii) The phase transition temperature range around the temperature of the maximum dielectric permittivity (Tm) becomes more and more broad. In addition, 0.98KNN-0.02LF ceramics exhibited a very stable temperature dependence of dielectric permittivity with permittivity maximum near 2000 and dielectric loss less than 4% in the temperature range of 0–400℃. The relaxation behavior of the 0.98KNN-0.02LF ceramics is interpreted in terms of polar nanoregions (PNRs) caused by cations disorder. The P-E hysteresis loops further confirms the relaxor behavior in 0.98KNN-0.02LF ceramics.
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