Electric fatigue process in lead-free alkali niobate ceramics at various pressures and temperatures

Electric fatigue tests are important for evaluating the reliability of piezoceramics. However, these tests have not been the focus of studies of lead-free alkali niobate (NKN) ceramics so far. For this purpose, two different materials, Li0.06Na0.47K0.47NbO3 (LNKN6) and Na0.55K0.45NbO3 + 0.25% MnO (Mn-NKN), have been examined at various uniaxial pressures ranging from 0.1 to 100MPa and various temperatures ranging from room temperature to 150 degrees C. It was shown that the harder ferroelectric Mn-NKN could maintain its piezoelectric properties at pressures up to 25MPa. When bipolar fatigue occurred under pressures over the coercive stress of similar to 30MPa, the sample depolarized and formed microcracks. In contrast, the softer LNKN6 did not show fatigue at higher pressures between 25 and 50 MPa. However, in both materials, higher temperatures enhanced domain wall and charge carrier movements and conclusively domain wall pinning. (C) 2015 The Japan Society of Applied Physics