Piezoelectric properties of (K, Na)NbO3 thin films deposited on (001)SrRuO3/Pt/MgO substrates

Thin films of Pb-free single crystal (K
_x
Na
_1-x
)NbO
₃
, KNN, were epitaxially grown on (001)SrRuO
₃
/ (001)Pt / (001)MgO substrates by rf-magnetron sputtering. In the pseudo-tetragonal system, c-lattice parameters of the sputtered KNN films were around 1% longer than those of the bulk KNN. The sputtered KNN thin films showed bulk like dielectric properties and/or ferroelectricity. Dielectric constant epsiv
_r
spontaneous polarization P
_s
, and coercive electric field E
_c
of KNN (x= 0.1: (K
_0.1
, Na
_0.9
)NbO
₃
) were 300, 20 [muC/cm
²
] and 50 [kV/cm], respectively. The piezoelectric coefficient e
₃₁
of NaNbO
₃
(NN) films was e
₃₁
*= -0.7 [C/m
²
], which was 60% of e
₃₁
of bulk NN ceramics. On the other hand, the piezoelectric properties increased with the doping of K and KNN (x=0.1) showed relatively large e
₃₁
* of-2.4 [C/m
²
].