International audienceFerroelectric and multiferroic materials present a nonlinear variation in their permittivity due to domain wall motion. Currently, this variation is described either by the Rayleigh law for fields above a threshold or by a power law for soft ferroelectrics. We propose a hyperbolic law based on the contributions of domain walls and intrinsic lattice which includes the two classic approaches. The threshold field is clearly defined by considering reversible and irreversible components of the permittivity. A good agreement between the hyperbolic law and experimental data is obtained. Moreover, we show that the threshold field obeys to the Volgel-Fulcher law

In the present paper, the influence of manganese doping on the dielectric properties of BaSrTiO 3 thin films is presented. The real and imaginary parts of the material's permittivity have been measured in a large frequency range (100 Hz-1 MHz) and as a function of the electric field. The tunability and the figure of merit of the material have been obtained from the measurement of the permittivity under an applied DC bias electric field. For the undoped material, the dielectric losses become important for a large DC bias which leads to breakdown. At a suitable dopant rate, this effect disappears. In order to better understand the origin of the related phenomena, we measure the permittivity as a function of the AC excitation amplitude and we decompose the obtained permittivity with the hyperbolic law. This enables to extract the different contributions of the bulk (low frequency diffusion and high frequency lattice relaxation) and of the domain wall motions (vibration and pinning/unpinning) to the material's dielectric permittivity and to understand the effect of manganese doping on each contribution. Knowledge of the related mechanisms allows us to establish the optimum dopant rate (mainly conditioned by the lattice contribution) and to reduce the domain wall motion, which finally is beneficial for the desired properties of the ferroelectric thin film. A particular attention is paid to low frequency diffusion, an especially harmful effect when a DC biasing is mandatory (tunable electronic component in mobile telecommunication devices for example).

In this paper, the different contributions to the permittivity of a 1% manganese-doped BaSrTiO 3 thin film are presented as a function of the applied DC field. The hyperbolic law has been used to discern the lattice, domain wall vibration, and pinning/unpinning contributions. This decomposition permits us to study the weight of the respective contribution in the total permittivity, the losses, and the tunability. By determining the figure of merit (FoM) of each contribution, the ratio between tunability and losses, it is possible to identify the phenomenon which should be limited or enhanced in order to optimize the material's dielectric properties. It is shown that the tunability of the domain wall contribution (approximately 80%) is very important compared to the lattice contribution (41%), the associated dissipation factor, however, is also much larger (0.2 instead of 0.014). Even if the domain wall contribution has been shown to be weak in the investigated thin film (less than 3% in permittivity and tunability), the weight of the losses is not negligible (around 18%). Hence, the domain contribution has to be limited in order to conserve a high FoM for the material. Moreover, it is shown that the AC field used for the material's characterization is important because it governs the weight of the domain wall losses and thus the FoM. V C 2016 AIP Publishing LLC.

Enhancement of lead zirconate (PbZrO3) polarization is achieved by using a titanium seed layer on alumina polycrystalline substrate. Thanks to the reduction of the lattice mismatch between the platinum electrode (3.92 Å) and the PbZrO3 films (4.14 Å), lead zirconate thin films oriented along the (111) direction with an orientation factor of around 65 % has been obtained. The (111) PbZrO3 presents an increase of 56% of the polarization compared to the (100) PbZrO3. This enhancement is responsible of the higher recoverable energy storage density obtained in the (111) PbZrO3 thin films (8 J/cm 3 at 600 kV/cm with an efficiency of 72%). The (111) PbZrO3 also has a higher figure of merit, which indicates that the (111) crystallographic plan is the most favorable direction for energy storage.

Two Pb(Zr0.20Ti0.80)O3 samples of different thickness and domain configuration have been studied. The c-domain sample was found to have a higher coercive field E c and higher dielectric losses than the other which presents approximately 60% of c-domains and 40% of a-domains as observed by piezo force microscopy (PFM) characterization. Hyperbolic law measurements reveal that the higher coercive field is due to domain wall pinning in deeper defects and hence a higher field E th is required for unpinning. The dissipation factors due to domain wall motion, however, are similar in both samples since the domain wall density is low and there is almost no interaction between domain walls. The higher dielectric losses in the c-domain oriented sample are a result of a greater contribution from the lattice and seem to be due to strain from the substrate, which is not relieved in a thin sample. PFM and dielectric characterization are complementary methods which provide a better understanding of the domain wall motion.

In this study, two different methods have been used in order to characterize leadzirconate anti-ferroelectric thin film elaborated by a modified sol-gel process: First-Order Reversal Curves (FORC) measurements and impedance spectroscopy coupled to hyperbolic law analysis. Approaches at low and high applied electric fields allow concluding on the presence of a weak residual ferroelectric behavior even if this contribution is not visible on the polarization-electric field loops. Moreover, the weak ferroelectric phase seems to switch only when the phase of the antiferroelectric cells is modified and no coalescence of ferroelectric domains at low field occurs due to a well distribution of small residual ferroelectric clusters in the material. The main goal of this paper is to show that FORC distribution measurements and impedance spectroscopy coupled to the hyperbolic law analysis are very sensitive and complementary methods.

International audienceThis work deals with the design, realization and characterization of a miniature and frequency agileantenna based on a ferroelectric Ba0,80Sr0,20TiO3 thinfilm. The notch antenna is loaded with a variablemetal/insulator/metal (MIM) capacitor and is achieved by a monolithic method. The MIM capacitance is3.7 pF, which results in a resonant frequency of 670 MHz compared to 2.25 GHz for the unloadedsimulated antenna; the resulting miniaturization rate is 70%. The characterization of the antennaprototype shows a frequency tunable rate of 14.5% under an electricfield of 375 kV/cm, with a tunabilityperformance h = 0.04

International audienceFerroelectric materials subjected to a DC electric field have their dielectric permittivity which decreases with time. This is connected to the reorganization of the domain walls to achieve a more stable configuration. We propose here to study the domain walls motion when the material is subjected to an electrical field. We use the hyperbolic law (generalized Rayleigh law) for contributions related to the walls. This allows to clearly identifying the domain walls as responsible for the time decay of the permittivity