Low‐Temperature Sintering of Bi _0.5 (Na,K) _0.5 TiO ₃ for Multilayer Ceramic Actuators

Abstract

We investigated the influence of CuO amount (0.5–3.0 mol%), sintering temperature (900°C–1000°C), and sintering time (2–6 h) on the low‐temperature sintering behavior of CuO‐added Bi 0.5 (Na 0.78 K 0.22 ) 0.5 TiO 3 ( BNKT 22) ceramics. Normalized strain ( S max / E max ), piezoelectric coefficient ( d 33 ), and remanent polarization ( P r ) of 1.0 mol% CuO‐added BNKT 22 ceramics sintered at 950°C for 4 h was 280 pm/V, 180 pC/N, and 28 μC/cm 2 , respectively. These values are similar to those of pure BNKT 22 ceramics sintered at 1150°C. In addition, we investigated the performance of multilayer ceramic actuators made from CuO‐added BNKT 22 in acoustic sound speaker devices. A prototype sound speaker device showed similar output sound pressure levels as a Pb(Zr,Ti)O 3 ‐based device in the frequency range 0.66–20 kHz. This result highlights the feasibility of using low‐cost multilayer ceramic devices made of lead‐free BNKT ‐based piezoelectric materials in sound speaker devices.