Influence of sintering temperature on microstructure and electric properties of CuO doped alkaline niobate-based lead-free ceramics

In this work, microstructure characteristics, dielectric, piezoelectric and ferroelectric properties of lead-free (K0.4425Na0.52Li0.0375)(Nb0.87Ta0.06Sb0.07)O-3 (KNLNST) doped with 1 mol% copper oxide (CuO) piezoelectric ceramics prepared by a conventional solid-state reaction route are investigated with an emphasis on the influence of sintering temperature. The introduction of CuO could significantly improve the sinterability of KNLNST ceramics. It is found that the tetragonality of the ceramics increases with raising sintering temperature. A dense microstructure with increased grains is developed, probably due to liquid-phase sintering. Both the piezoelectric constant d (33) and planar electromechanical coupling k (p) increase with increasing relative density and grain size. The Curie temperature T (C) values increase slightly when the sintering temperature is increased. In addition, the KNLNST ceramics doped with 1 mol% CuO show obvious dielectric relaxor characteristics, and the relaxor behavior of ceramics is strengthened by increasing the sintering temperature. The improved piezoelectric and dielectric properties of d (33) = 241 pC/N, k (p) = 0.437, dielectric loss tan delta = 0.0087, mechanical quality factor Q (m) = 138, dielectric constant epsilon (r) = 1,304 can be obtained for specimens sintered at 1,080 A degrees C for 3 h.