Influence of A-site deficiency on oxygen-vacancy-related dielectric relaxation, electrical and temperature stability properties of CuO-doped NKN-based piezoelectric ceramics

The lead-free ceramics with composition of (Na0.5K0.5)(0.9975-x)Ca0.0025NbO3+1 mol% CuO (NKN - 100x - C - 1,where x=0, 0.02, 0.03, 0.04, 0.06, 0.08) were synthesized by the mixed-oxide method at a sintering temperature of 1080 degrees C. Effects of Na and K deficiency amounts of x on the oxygen vacancies relating to the electrical and temperature stability properties were systematically investigated. Experimental results showed that the bulk densities of composition ceramics increased with increasing x contents due to the sintering aid of TTB formation at the grain boundary. The electrical properties of NKCN - 100x - C - 1 ceramics exhibited the optimum values: bulk density rho similar to 4.45 g/cm(3), dielectric constant (epsilon(T)(33)/epsilon(0)) similar to 255, dielectric loss (tan delta)similar to 0.003, k(p) similar to 0.38, k(t) similar to 0.49, g(33) similar to 39 x 10(-3) V-m/N, and Q(m) similar to 2850. Furthermore, the change rate of k(p) and Q(m) versus temperature (TCk(p) and TCQ(m)) could increase by 7% and 35% in the temperature range 20-120 degrees C, respectively. This may be due to the decrease of mechanical damping. The imaginary part impedance of NKN - 100x - C - 1 ceramics with the x variation was evaluated, and the activation energy was correspondingly calculated, which disclosed the deficient x amounts correlating with the oxygen vacancy and high Q(m) value. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.