High Piezoelectric Properties of KNN-Based Thick Films with Abnormal Grain Growth

Over 10 mu m-thick (K,Na)NbO3 KNN-based films doped with complex-perovskite-materials (CPs) were deposited on platinized sapphire substrates by aerosol deposition (AD). Three CPs were selected: Ba(Cu1/3Nb2/3)O3 (BCN), Cu(Cu1/3Nb2/3)O3 (CCN), and Sr(Cu1/3Nb2/3)O3 (SCN). The films of 0.985(Na0.5K0.5)NbO3-0.015CPs (KNN-CPs) were post annealed at 1050 degrees C for 1h in air without any serious phase decomposition. The microstructure showed abnormal grain growth due to Cu-rich liquid phase. The KNNBCN film had the largest abnormal grain size of over 10 mu m, whereas the KNNSCN film had the smallest grain size and also the smallest frequency of abnormal grains. All the films exhibited typical characteristics of ferroelectric hysteresis similar to those of the bulk materials without any leakage. The KNNBCN films possessing the biggest abnormal grains also exhibited the highest density, piezoelectric constant, and piezoelectric voltage constant of 110pC/N and 15.45 x 10(-3)Vm/N, respectively, which are the highest values reported so far for KNN-based films. This indicated that KNN-CPs lead-free films are suitable candidates for sensor applications.