Phase Structure, Microstructure and Electrical Properties of Lead-Free (1-x) Na_(0.515)K_(0.485)_(0.94)Li_(0.06)(Nb_(0.99)Ta_(0.01))O_3 Ceramics

摘要

Lead-free (1-x)[ (Na_(0.515)K_(0.485))_(0.94)Li_(0.06)(Nb_(0.99)Ta_(0.01))O_3]-xBiAlO_3 (NKLNT-BA; x = 0, 0.005, 0.010, 0.015, and 0.020) ceramics were fabricated by a conventional mixed-oxide method. The effects of BiAlO_3 addition on the phase structure, microstructure and electrical properties of ceramic were then studied. The result indicated that grain size decreased with increasing of BiAlO_3 content. In the composition range studied, the perovskite phase with the coexistence of the orthorhombic and tetragonal phases was identified at approximately x ≤ 0.005 by the X-ray diffraction analysis and dielectric spectroscopy, which led to a significant enhancement of the piezoelectric properties. The tetragonality increased with further increasing x. The temperature dependence of dielectric properties showed that the addition of BiAlO_3 slightly decreased the ferroelectric tetragonal-paraelectric cubic phase transition temperature (TC), but greatly shifted the polymorphic phase transition from the ferroelectric orthorhombic to the ferroelectric tetragonal phase (TO-T) to lower room temperature. The dielectric and piezoelectric properties are enhanced for the composition near the orthorhombic-tetragonal polymorphic phase boundary. The unmodified- (Na_(0.515)K_(0.485))_(0.94)Li_(0.06)(Nb_(0.99)Ta_(0.01))O_3 ceramics exhibit optimum electrical properties (d_(33) = 225 pC/N and T_C = 418°C).