Lead-free piezoelectric ceramics with ultralow mechanical quality factor

The mechanical quality factor ( Q m ) is a key parameter in the applications of piezoelectric ceramics. For force sensors and acoustic transducers, low Q m allows a broadened frequency range for signal reception. Currently, the most popular low- Q m materials are lead-based ferroelectric ceramics, such as PbNb 2 O 6 . However, restrictive regulations on Pb-containing components have prompted the search for alternative lead-free piezoelectrics. Some studies on low- Q m lead-free ceramics have been reported, but without clarifying its origin. Here, lead-free piezoceramics with a nominal composition K 0.475 Na 0.475 Bi 0.025 Ag 0.025 Nb 0.95 Hf 0.05 O 3 (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 K 0.50 Na 0.50 NbO 3 (KNN). The KNN-BAH ceramics sintered at 1080 °C and 1120 °C showed Q m values of about 27.2 and 57.1, respectively, which are among the lowest values reported for lead-free piezoelectric ceramics. The ultralow Q m is attributed to the bi-phasic structure and enhanced domain wall motion.