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Single-phase perovskite ceramics were synthesized using a Pb-free (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 (LF4) piezoelectric material both with and without CuO as a dopant additive. Bipolar hysteresis measurements showed a relatively high remanent polarization (20 μC/cm2, 16 μC/ cm2) and maximum polarization (25 μC/cm2, 21 μC/cm2) values were found for undoped LF4 and 0.2 wt% CuO-doped LF4, respectively. Unipolar fatigue behavior for this system was found to decrease strongly with increased applied testing fields and increased test durations. For undoped LF4, the maximum polarization values were stable after 10 cycles after testing for 100,000 cycles duration. For the CuO-doped samples, increasing the testing field to 3EC resulted in twice the decrease in PMAX (-32%) compared with the 2EC tests at 106 cycles (-17%). At 2EC testing for CuO doping, polarization decreases continually through 107 cycles, with the decreases in PMAX and d33 both reaching a maximum (-22% and -30%, respectively) after 107 cycles. In the CuO-doped samples, the fatigue is exacerbated because of the influence of space charge on the increased number of defects present.