Piezoelectric voltage constant and sensitivity enhancements through phase boundary structure control of lead-free (K,Na)NbO3-based ceramics

The piezoelectric voltage constant (g(33)) is a material parameter critical to piezoelectric voltage-type sensors for detecting vibrations or strains. Here, we report a lead-free (K,Na)NbO3 (KNN)-based piezoelectric accelerometer with voltage sensitivity enhanced by taking advantage of a high g(33). To achieve a high g(33), the magnitudes of piezoelectric charge constant d(33) and dielectric permittivity epsilon(r) of KNN were best coupled by manipulating the intrinsic polymorphic phase boundaries effectively with the help of Bi-based perovskite oxide additives. For the KNN composition that derives benefit from the combination of epsilon(r) and d(33), the value of g(33) was found to be 46.9 x 10(-3) V.m/N, which is significantly higher than those (20 - 30 x 10(-3) V.m/N) found in well-known polycrystalline lead-based ceramics including commercial Pb(Zr,Ti)O-3 (PZT). Finally, the accelerometer sensor prototype built using the modified KNN composition demonstrated higher voltage sensitivity (183 mV/g) when measuring vibrations, showing a 29% increase against the PZT-based sensor (142 mV/g).