Phase transition and electrical properties of (K0.5Na 0.5)(Nb1-xTax)O3 lead-free piezoelectric ceramics

摘要

(K0.5Na0.5)(Nb1-xTax)O 3 lead-free piezoelectric ceramics have been prepared by an ordinary sintering technique. The results of X-ray diffraction reveal that Ta 5+ diffuses into the K0.5Na0.5NbO3 lattices to form a solid solution with an orthorhombic perovskite structure. Because of the high melting temperature of KTaO3, the (K 0.5Na0.5)(Nb1-xTax)O3 ceramics can be sintered at higher temperatures. The partial substitution of Ta5+ for the B-site ion Nb5+ decreases both paraelectric/cubic-ferroelectric/tetragonal and ferroelectric/tetragonal- ferroelectric/orthorhombic phase transition temperatures, TC and TO-T. It also induces a relaxor phase transition and weakens the ferroelectricity of the ceramics. The ceramics become 'softened', leading to improvements in d33, kp, kt and εr and a decease in Ec, Qm and N p. The ceramics with x=0.075-0.15 become optimum, having d 33=127-151 pC/N, kp=0.43-0.44, kt=0.43-0.44, εr=541-712, tanδ=1.75-2.48% and TC=378-329 °C.