Ferroelectric order driven Eu3+ photoluminescence in BaZrxTi1−xO3 perovskite

The 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

Synthesis and characterization of BaTiO3/-Fe2O3 core/shell structure

Multiferroic materials attracted a lot of attention in recent years because of their significant scientific interest and technological applications. The multiferroic core/shell powders have a better connectivity between the phases, resulting in superior dielectric and magneto electric properties. In this study, the influence of preparation condition on structure and properties of BaTiO3/-Fe2O3 core/shell composite materials was examined. The five samples were obtained by varying synthesis conditions, such as synthesized method (co-precipitation and sonochemical method) and pH values of solution. XRD and Raman spectroscopy analyses were performed in order to determine phase composition and structural changes within samples. Morphology modifications were examined by SEM and EDS analyses. Finally, effect of structural and microstructural changes on magnetic and electrical properties was detected and explained

Properties of the Pb(Mg1/3Nb2/3)O3 Ceramics Prepared by Using Two Different Mg Precursors

Pb(Mg1/3Nb2/3)O3 ceramics prepared via columbite method by using two types of Mg precursors, i.e. MgO and (MgCO3)4\ub7Mg(OH)2\ub74H2O exhibit high crystallinity and high densification after sintering at 1200\ub0C. Higher amounts of pyrochlore phases were detected in the PMN sample obtained by using (MgCO3)4\ub7 Mg(OH)2.4H2O as precursor. This compositional difference, determines, for all frequencies, a shift of 3c 50 K of the temperature corresponding to the permittivity maximum Tm for the sample derived from (MgCO3)4\ub7Mg(OH)2\ub74H2O. 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

Raman investigation and functional characterization of (Pb(0.8)La(0.2))(Mg(0.4)Nb(0.6))O(3) ceramics prepared by the columbite method

(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

Impedance spectroscopy method for investigation of the polycrystalline inhomogeneous ceramics

The present paper introduces the principles of the Impedance Spectroscopy technique, as an important method in the characterization of the discrete materials working in real conditions in circuits. The method was firstly verified by using an RC series-parallel circuit and then was exemplified in studying two types of (Ni, Zn) ferrite ceramics

Nonlinear properties of antimony-doped BaTiO3 ceramics

Barium titanate nanopowders doped with various concentrations of antimony were synthesized by polymeric precursors method based on modified Pechini process. Obtained powders were pressed and sintered at 1,573 K for 8 h. The temperature dependence of dielectric permittivity pointed on the significant influence of added antimony on dielectric properties of obtained materials. The analysis of impedance spectrum in the temperature range 250-445 K has shown the presence of one semicircle that corresponds to the grain contribution but impedance spectrum at 773 K showed possible overlapping of two semicircles indicating also grain boundary resistivity. The total specific resistivity obtained from impedance analysis showed modest PTCR jump in the heavily doped barium titanate ceramics. The electric field dependence of permittivity of the ceramics was investigated in detail. The experimental data were analyzed using Johnson model