Multiferroic response of nanocrystalline lithium niobate J. Appl. Phys. 111, 07D907 (2012) Non-radiative complete surface acoustic wave bandgap for finite-depth holey phononic crystal in lithium niobate Offsets of hysteresis loops along the polarization axis have been observed on a step graded Pb͑Zr,Ti͒O 3 ͑PZT͒ thin film using a Sawyer-Tower ͑ST͒ circuit. However, the same effect may be artificially reproduced by adding adequate resistors and diodes in parallel with a nongraded PZT thin film. The hypothesis that the offsets were mainly due to the asymmetrical charging up of the standard capacitor used in the ST circuit, allows us to establish that the graded ferroelectric sample behaves as a kind of rectifying device. It is concluded that the presence of asymmetrical leakage currents in compositionally graded devices may allow the elucidation of the origin of the offsets often observed in these structures. Correlatively, it is demonstrated that such offsets do not represent an abnormal static polarization but a dc voltage. The E m 4 power law dependence of the offsets ͑where E m is the amplitude of the electric field͒ was found to be attributable to the nonlinear increase of the net leakage current.

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The ferroelectric properties of Pt∕Pb(Zr0.6Ti0.4)O3∕Pt∕TiO2∕SiO2∕Si thin-film capacitors with different thicknesses are investigated. According to the literature data, tilting of the hysteresis loops and marked increase of the coercive fields are observed when the thickness of the film is reduced. The degradation of the switching properties is fully reproduced by simulations including nonferroelectric space-charge layers at both ferroelectric/electrode interfaces. Based on the theoretical results, a converse model is constructed from which the overall interface capacitance, the total interface built-in potential, and both dielectric permittivity and polarization of the bulk ferroelectric layer are determined for each film. Remarkably the polarization loop due to the switching domains, calculated for each Pb(Zr,Ti)O3 (PZT) capacitor, exhibited a squarelike shape with coercive fields in agreement with the bulk value. Moreover, a unique set of parameters was found whatever the film thickness. From our results it is concluded that the degradation of the ferroelectric properties of metal-PZT thin-film-metal capacitors, often encountered when their thickness is reduced, probably arises from a mechanism of modulation of density and sign of the space charge at both interfaces.