Small Reduction of the Piezoelectric d 33 Response in Potassium Sodium Niobate Thick Films

We have investigated the electromechanical response of potassium sodium niobate ( K 0.5 Na 0.5 NbO 3 or KNN ) thick films. The high‐field strain hysteresis loops and weak‐field converse piezoelectric d 33 coefficient of the films were measured and compared with those of KNN bulk ceramics under the same electric field conditions. The converse d 33 values of the thick films and bulk ceramics were equal to 82.5 and 138 pm/V, respectively, at 0.4 kV/mm. The fundamental difference between the piezoelectric response of the KNN films and the ceramics was studied in terms of the effective (“clamped”) piezoelectric d 33 coefficient. The reduction in the piezoelectric d 33 coefficient of the KNN films, resulting from the clamping by the substrate, was compared to lead‐based ferroelectric thick films, including Pb ( Zr , Ti ) O 3 ( PZT ) and (1 −  x ) Pb ( Mg 1/3 Nb 2/3 ) O 3 − x PbTiO 3 ( PMN ‐ PT ). We propose a possible explanation, based on the particular elastic properties of KNN , for the small relative difference observed between the “clamped” and “unclamped” (“bulk”) d 33 of KNN , in comparison with lead‐based systems.