Piezoelectric properties of (Na _{1− <i>x</i>} K _<i>x</i> )NbO ₃ ‐based lead‐free piezoelectric ceramics and their application in knocking sensor

Abstract

Abstract Piezoelectric knocking sensors with a dense microstructure were fabricated at 960°C for 2 hours using various CuO‐added (Na 0.5 K 0.5 )NbO 3 ( NKN )‐based piezoelectric ceramics. The practical sensitivity ( S P ) of the knocking sensor, which is the ability to detect the knocking of a car engine, was influenced by the g 33 × k p value of the piezoelectric ceramics, indicating that the g 33 × k p can be considered a figure of merit of the piezoelectric ceramics used in the knocking sensor. The knocking sensor synthesized using the CuO‐added 0.95(Na 0.5 K 0.5 )(Nb 0.95 Sb 0.05 )O 3 –0.05CaTiO 3 ( CNKNS – CT ) ceramic, which showed a g 33 of 25.7 Vm/N and k p of 0.46, exhibited a high S P of 119 mV /g at the resonance frequency. The S P of the commercial knocking sensor, which was synthesized using the Pb(Zr,Ti)O 3 ( PZT )‐based ceramic, was 112 mV /g at the resonance frequency. Hence, the knocking sensor fabricated using the CNKNS – CT piezoelectric ceramic can be used to replace the commercial PZT ‐based knocking sensor.