Abstract
Abstract In this work, for CuO-modified perovskite KNbO3 (KN-xCuO), by selecting the appropriate external field conditions (including chemical composition, direct/alternating E-field, time, temperature and bipolar cycles), we report the superior piezoelectric responses (incipient large-field piezoelectric responses d33*=1994 pm/V, Smax>0.3 %). Combined with the theoretical and experimental analysis, this work indicates that the unusual ferroelectric and electro-strain behaviors may be attributed to the discrepancies of characteristic frequency for defect dipoles transformation (CuNb-Vab1 and CuNb-Vab2) and ferroelectric domains switching. Different external fields affect the transformation process of defect dipoles, leading to the different constructing and restoring behaviors during the E-field loading and unloading process. After selecting the appropriate external field conditions, the large and stable electro-strain behaviors (maximum electro-strain Smax>0.3 % exhibits 2.6 % decline after 105 cycles at room temperature) are observed for the d.c.-poled and one-year-aged x=0.015 samples. This research may provide a paradigm for designing the high-performance KNbO3-based perovskite ferroelectrics by exploring the greatest potential of dynamic defect dipoles.
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