Piezoelectric nonlinearity in ferroelectric thin films

The piezoelectric properties of {001} oriented 0.5Pb(Yb _1/2Nb _1/2)O ₃-0.5PbTiO ₃ films were studied. It was found that the films show Rayleigh-like behavior in that the magnitude of the piezoelectric coefficient depends linearly on the amplitude of the exciting ac electric field used for the measurement. The reversible and irreversible Rayleigh piezoelectric coefficients decreased logarithmically with frequency. The frequency dependence of the Rayleigh coefficients measured under applied bias was identical for the dielectric and piezoelectric responses, suggesting that the same interface motion is responsible for both phenomena. It is demonstrated that dynamic poling of the material by the external ac field self-consistently explains both the Rayleigh-like response and the higher harmonics in the strain response.