117,339 research outputs found
Properties of the Pb(Mg1/3Nb2/3)O3 Ceramics Prepared by Using Two Different Mg Precursors
No full textPb(Mg1/3Nb2/3)O3 ceramics prepared via columbite method by using two types of Mg precursors, i.e. MgO and (MgCO3)4·Mg(OH)2·4H2O exhibit high crystallinity and high densification after sintering at 1200°C. Higher amounts of pyrochlore phases were detected in the PMN sample obtained by using (MgCO3)4· Mg(OH)2.4H2O as precursor. This compositional difference, determines, for all frequencies, a shift of ∼ 50 K of the temperature corresponding to the permittivity maximum Tm for the sample derived from (MgCO3)4·Mg(OH)2·4H2O. From this reason, better dielectric properties were obtained at room temperature for this PMN sample, although a higher dielectric permittivity at Tm was obtained for the sample derived from MgO precursor
Dieletric properties and Raman characterization of the Pb(Mg1/3Nb2/3)O3 ceramics prepared by using two different Mg precursors
No full textEvidence of the relaxor-paraelectric phase transition in Pb(Fe2/3W1/3)O3 ceramics
No full textThe transition relaxor-paraelectric in Pb(Fe2/3W1/3)O3 ceramics was studied by x-ray diffraction and Raman scattering at temperatures in the range of 85–800 K. For high diffraction angles (160° and 162°), a slight difference between the two phases was found. Raman spectra show an evolution with temperature with anomalies of bands of 848 cm−1 and 147 cm−1 (shift and intensity) in the Curie range of temperatures. This behavior is interpreted as an experimental evidence of perturbations of the nanopolar ordering related to the phase transition
Magnetic and dielectric properties of cobalt ferrite/titania composites
No full textIn order to develop materials with both magnetic and dielectric properties, recently a lot of researchers concentrate their work to process and study composite ceramics with both magnetic and dielectric phases. Cobalt ferrite Co Fe2O4 and TiO2 are good candidates for this type of composites as they have good magnetic and dielectric properties respectively.
New cobalt ferrite/titania (CFO/TO) ceramics composites were prepared by conventional solid state reaction with a CFO/TO ratio ranging from 2 to 8. Composition, crystalline structure and microstructure of the sintered ceramic composite bodies were investigated and the phases content volume percentage were determined. Dielectric permittivity ( real part of permittivity and dielectric losses) and magnetic permeability (real part of permeability and magnetic losses) were measured at room temperature in a range of frequency from 100 Mhz-1 GHz. Dielectric and magnetic properties were analyzed as function of the microscopic structure (SEM analysis) and phase compositions (XRD analysis). The formation of the ternary compound (FCTO) was found in composites with the TO/CFO bigger than 3
Raman investigation of the composition and temperature-induced phase transition in (1−x)Pb(Fe2∕3W1∕3)O3-xPbTiO3 ceramics
No full textThe evolution with temperature of the Raman activity in the (1−x)Pb(Fe2∕3W1∕3)O3-xPbTiO3 solid solution with various compositions x∊(0, 1) was investigated. By increasing x, a general evolution of the system from disordered relaxor to ordered ferroelectric state with typical lines also observed in other Pb-based relaxors were found. The Raman activity present at few hundred degrees above the Curie region confirms the thermal stability of the nanopolar ordered regions in a nonordered average cubic state. For all the examined samples, the position, intensity, or damping of a few Raman lines exhibit anomalies in a range of temperatures which was considered related to the Curie region. The range of Curie regions corresponding to each composition is in very good agreement with the shift of Curie temperature as a function of x found by previous dielectric investigations. Two sharp peaks in the Pb(Fe2∕3W1∕3)O3 spectra showed a maximum of their intensity at ≈500 K. This behavior is interpreted as due to critical changes in the dynamics of the nanopolar clusters at the freezing Burns temperatures in the present relaxor system
Raman investigation and functional characterization of (Pb0.8La0.2)(Mg0.4Nb0.6)O3 ceramics prepared by the columbite method
No full text(Pb(0.8)La(0.2))(Mg(0.4)Nb(0.6))O(3) relaxor ceramics have been prepared by columbite method by using (i) MgO and (ii)(MgCO(3))(4)center dot Mg(OH)(2)center dot 4H(2)O precursors (denoted as PLMN1 and PLMN2 respectively). The dielectric data show relaxor behaviour in the frequency range of 10 Hz to 1 MHz, with dielectric constant values in the range of 310-350 for PLMN1 and 240-260 for PLMN2 and a permittivity maxima at the temperature T(m)=179 K and T(m)=174K, respectively (for f=1 MHz). The Raman spectra proved the stability of the nanopolar order far above T, as observed in many Pb-based relaxors. This is demonstrated by the existence of some modes (at similar to 300, 500 and 780 cm(-1)) up to around 773K. Anomalies of some Raman modes (integrated intensity and FWHM) have been found in the range of T(m), proving the phase transition from pseudo-cubic relaxor to cubic paraelectric state, where the stability of the vibration modes is affected by the fluctuations associated to the phase transitions. (C) 2010 Elsevier B.V. All rights reserved
Ferroelectric order driven Eu3+ photoluminescence in BaZrxTi1−xO3 perovskite
No full textThe ability to tune and enhance the properties of luminescent materials is essential for enlarging their application potential. Recently, the modulation of the photoluminescence emission of lanthanide-doped ferroelectric perovskites by applying an electric field has been reported. Herein, we show that the ferroelectric order and, more generally the polar order, has a direct effect on the photoluminescence of Eu3+ in the model BaZrxTi1-xO3 perovskite even in the absence of an external field. The dipole arrangement evolves with increasing xfrom long-range ferroelectric order to short-range order typical of relaxors until the non-polar paraelectric BaZrO3 is achieved. The cooperative polar interactions existing in the lattice (x < 1) promote the off-center displacement of the Eu3+ ion determining a change of the lanthanide site symmetry and, consequently, an abrupt variation of the photoluminescence emission with temperature. Each type of polar order is characterized by a distinct photoluminescence behaviour
New broadband button-shaped antenna on innovative magneto-dielectric material for wearable applications
No full textThe design and characterization of a new broadband small patch antenna, based on an innovative magneto-dielectric material and suitable for wearable applications at 868 MHz, is presented. To reduce antenna dimensions while preserving its radiation and matching performances, a barium-strontium hexaferrite Ba0.75Sr0.25Fe12O19 has been synthesized to achieve a magnetic permeability double than vacuum in the band of interest. The material is first experimentally characterized and the dispersive permittivity and permeability behaviors are accounted for during the design of a small patch antenna with a shorting-plate. Very good agreement with measurements is demonstrated for both matching and radiation performances of the antenna
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