Effects of Li Substitution on the Structure and Ferroelectricity of (Na,K)NbO_3

摘要

The structures of (1-x)(K_(0.5)Na_(0.5))NbO_(3-x)LiNbO_3 were investigated by the X-ray Rietveld method at room temperature. It is surprising to find that the spontaneous polarization of ortho-rhombic phase reaches at the lowest value and the spontaneous polarization of tetragonal phase reaches at highest value at x = 0.06. The lattice parameter of(K_(0.47)Na_(0.47))NbO_3-0.06LiNbO_3, which was refined by using two phase model, reasonably described the structure change of the (1x)(K_(0.5)Na_(0.5))NbO_3-xLiNbO_3. The temperature dependence of Raman spectroscopy study of the phase transition of(K_(0.47)Na_(0.47))NbO_3-0.06LiNbO_3 showed that the increasing of temperature introduced a local disorder even above T_c. The degree of cation ordering determines the electrical properties of the ceramics.