Sintering and piezoelectric properties of KNN ceramics doped with KZT

This paper investigates the effect of K
_1.94
Zn
_1.06
Ta
_5.19
O
₁₅
(KZT) addition on the sintering behavior and piezoelectric properties in lead-free piezoelectric ceramics of (K
_0.5
Na
_0.5
)NbO
₃
(KNN). The apparent density of sintered KNN ceramics was increased with KZT addition, and a relative density of above 96.3% was obtained with the doping of over 0.5 mol% KZT. The maximum dielectric and piezoelectric properties of epsiv
₃

^T
/epsiv
₀
= 590, d
₃₃
= 126 pC/N, k
_p
= 0.42, and P
_tau
, = 18 muC/cm
²
were obtained from 0.5 mol% KZT-doped KNN ceramics. A small amount of KZT (~0.5 mol%) was effective for improving the sintering behavior and piezoelectric properties, but KZT addition exceeding 1.0 mol% was effective only for den-siflcation. A small amount of KZT was effective for den-siflcation of KNN ceramics by promoting K
_5.75
Nb
_10.8
O
₃₀
liquid phase formation. However, even though KNN with 1.0~2.0 mol% KZT had a relative density of > 98.5%, the piezoelectric properties were inferior to those of 0.5 mol% KZT-doped KNN, presumably due to the smaller grain size and excess liquid phase of the KNN ceramics doped with higher amounts of KZT. It is believed that a small amount of KZT could be one of the suitable sintering aids to obtain highly dense KNN based piezoelectric.