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

摘要

The lead-free ceramics with composition of (Na_(o.5)K_(o.5))_(o.9975-x)Ca_(0.oo25)NbO_3 + l mol% CuO (NKN—100x—C — l,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 °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— l00x—C— 1 ceramics exhibited the optimum values: bulk density p ~ 4.45 g/cm3, dielectric constant (ε~T_(33)/ε_0) ~ 255, dielectric loss (tan<5)~0.003, k,, ~ 0.38, fct~ 0.49, g33 ~ 39 x 10"3 V-m/N, and gm~ 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 °C, respectively. This may be due to the decrease of mechanical damping. The imaginary part impedance of NKN— lOOx—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.