Lead-free piezoelectric ceramics with ultralow mechanical quality factor

Abstract

The mechanical quality factor (Qm) is a key parameter in the applications of piezoelectric ceramics. For force sensors and acoustic transducers, low Qm allows a broadened frequency range for signal reception. Currently, the most popular low-Qm materials are lead-based ferroelectric ceramics, such as PbNb2O6. However, restrictive regulations on Pb-containing components have prompted the search for alternative lead-free piezoelectrics. Some studies on low-Qm lead-free ceramics have been reported, but without clarifying its origin. Here, lead-free piezoceramics with a nominal composition K0.475Na0.475Bi0.025Ag0.025Nb0.95Hf0.05O3 (KNN-BAH) were developed by a partial substitution of K and Na at A-sites with Bi and Ag, and the Nb at B-sites with Hf in K0.50Na0.50NbO3 (KNN). The KNN-BAH ceramics sintered at 1080°C and 1120°C showed Qm values of about 27.2 and 57.1, respectively, which are among the lowest values reported for lead-free piezoelectric ceramics. The ultralow Qm is attributed to the bi-phasic structure and enhanced domain wall motion.