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

Thin films of Pb-free single crystal (K_xNa_1-x)NbO₃, KNN, were epitaxially grown on (001)SrRuO₃ / (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)NbO₃) were 300, 20 [muC/cm²] and 50 [kV/cm], respectively. The piezoelectric coefficient e₃₁ of NaNbO₃ (NN) films was e₃₁*= -0.7 [C/m²], which was 60% of e₃₁ 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 e₃₁* of-2.4 [C/m²].