Dielectric spectroscopy of soft modes in ferroelectrics
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Soft modes
Abstract Sol-gel derived PLZT, including PbTiO3, PbLaTiO3 28, PLZT 9/65/35 and PZT 53/47 films were prepared on platinized substrates. The dielectric and ferroelectric properties of the films were measured at 260K -580K. The values of polarization, coercive field dielectric constant and dissipation factor in these films typically increased with increasing temperature. The changes in dielectric properties of the films with temperature were not sharp unlike the transitions in single crystals or bulk ceramics. The pyroelectric coefficients, on the other hand, decreased monotonically with increasing temperature in all these films.
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Abstract This paper presents the results of the investigation of dielectric dispersion in semiconductive ferroelectric Sn2P2S6 crystals over the frequency range 1 kHz to 78.5 GHz. The main dielectric dispersion in Sn2P2S6 is caused by the soft ferroelectric Bu mode and in the vicinity of the Curie point it occurs in the millimeter region. The frequency of the soft mode in the paraelectric phase varies according to vs = 35 (T-Tc )½ GHz on approaching the Curie point. The soft mode is strongly overdamped. Close to Tc the relative damping is y/vs = 14. The dielectric contribution of the soft mode is equal to the static dielectric permittivity and it explains its whole temperature-dependence.
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AbstractMultilayer PZT thick film (∼10 μm) on Ti-metal substrate fabricated by aerosol deposition (AD) with LaNiO3 (LNO) top and bottom electrode and investigated their dielectric and ferroelectric properties. The film was found to be highly dense and crack free. The ferroelectric fatigue up to 109 bipolar switching cycles as well as the thermal shock (−30°C and 90°C) with 30 cycles test revealed no significant change in the remnant polarization, dielectric constant and dielectric loss was observed which shows the reliability of AD film. The temperature dependent dielectric and ferroelectric properties of PZT thick films were discussed in this paper.Keywords: PZTaerosol-depositionmultilayer thick filmLaNiO3ferroelectric fatigue Additional informationFundingThis research was supported by Global Frontier R&D Program (2013-073298) on Center for Hybrid Interface Materials (HIM) funded by the Ministry of Science, ICT & Future Planning and KIMS internal research program.
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Volume fraction
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Abstract In order to improve the dielectric strength of the PZT 95/5 type ferroelectric ceramics, Alumina and silica were used to form glass phase to add into them. The dielectric and ferroelectric properties of the ceramics with and without additives were compared. The results have shown that the dielectric strength was significantly enhanced (from 3.5KV/mm to 6KV/mm) and the other properties have no obvious change when the amount of additives was appropriate.
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The dielectric properties of ferroelectric Ba0.5Sr0.5TiO3 and non-ferroelectric MgO composites synthesized by using nano particles are investigated for tunable microwave applications. Dielectric properties are studied in the temperature range of −250°C to 100°C, with and without an electrical field. The dielectric tunability is ∼50% for BST:MgO composites under the field of 80 KV/cm. at around the Curie peak. The use of nano particle sizes of materials considerably reduces dielectric losses and shows comparatively high K-factor values in the resulted composites. The ferroelectric phase is well connected and thus enhances the overall dielectric properties of the composites.
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A series of composites were synthesized by solid-state reaction,with ferroelectric powder of BST and ferromagnetic powder of YIG as raw materials.Dielectric and magnetic properties of ferroelectric-ferromagnetic composites were tested.The results show that the ferroelectric/ferromagnetic composites sintered at proper temperature consist of ferroelectric phase and ferromagnetic phase.The composite materials xBST-(1-x)YIG(x=0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0) exhibit excellent dielectric and magnetic properties.Both e′ and e″ increase with the increase of BST content,and the dielectric resonant frequency shifts to a higher frequency with YIG content increasing.The permeability rises with BST content decreasing.The resonance frequency and high frequency characteristics of YIG are improved by adding BST.
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Ferromagnetic material properties
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Abstract The characteristic dielectric behaviour of ferroelectric liquid crystals with a large spontaneous polarization has been studied as functions of the D.C. bias field, frequency, cell thickness and applied pressure. Under the condition in which the contribution of the Goldstone mode is suppressed, a sharp peak in the temperature dependence of the dielectric constant is clearly observed at the transition between SA and S*C phases T S C *s A. The relaxation of the soft mode is observed both in the SA and S*C phases by eliminating the contribution of the Goldstone mode under a D.C. bias field. Another relaxation is also observed in the S*C phase around several kHz in addition to that of the soft mode and the Goldstone mode. The pressure effect on the soft mode was also studied.
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