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

Thin films of Pb- free single crystal (K,, Na1-xNbO3, 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 c, spontaneous polarization P,, and coercive electric field E-c of KNN (x= 0.1: (K-0.1, Na-0.9)NbO3) were 300, 20 mu C/cm(2)) and 50 [kV/cm], respectively. The piezoelectric coefficient e(31)* of NaNbO3 (NN) films was e(31)* congruent to -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)].