“…This Q m value, however, was similar to that of the 0.75PZT-0.25PZN-Mn ceramics sintered at 930 • C [19], indicating that the high Q m value of the CuO-added 0.75PZT-0.25PZN-Mn ceramics was mainly due to the hardening effect of the Mn ions. According to the previous works, most of the Mn ions existed as Mn 3+ in the PZT-based piezoelectric ceramics at the temperatures between 535 and 1080 • C [22,23]. Moreover, since all the specimens in this work were sintered at 850-950 • C, most of the Mn ions were considered to exist as the Mn 3+ ions and behave as the hardeners in the CuO-added 0.75PZT-0.25PZN-Mn ceramics.…”