Piezoelectric properties of epitaxial NaNbO3 thin films deposited on (001)SrRuO3/Pt/MgO substrates

Sodium niobate (NaNbO3, NN) thin films were deposited on (001)SrRuO3/Pt/MgO substrates by rf magnetron sputter deposition. The X-ray diffraction (XRD) pattern of the sputtered NN thin films showed epitaxial growth with a (001)-oriented perovskite structure. From the reciprocal space maps, the lattice parameters of the in-plane and out-of-plane directions were a = 0.392 nm and c = 0.395 nm, respectively. The relative dielectric constant E, and the range of the dielectric loss tan 6 were about 270 and 0.05-0.13 at 1 kHz, respectively. The P-E hysteresis loop showed clear ferroelectricity with spontaneous polarization P-s of 20 mu C/cm(2) and coercive electric field E-c of 50kV`/cm. The transverse piezoelectric properties were evaluated from the tip displacement of NN/MgO unimorph cantilevers. The transverse piezoelectric coefficient e(31)(*) (= d(31)/S-11(E)) was -0.9 C/m(2). which is almost compatible with that of the bulk NN ceramics. The tip deflection showed typical butterfly curves owing to the polarization reversal, indicating that the sputtered NN thin films had a high piezoelectric performance.