51 research outputs found
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
Hysteresis and tunability characteristics of Ba(Zr,Ti)O(3) ceramics described by first order reversal curves diagrams
The First Order Reversal Curves (FORC) diagrams are proposed for the characterization of the switching process and the tunability in Ba(ZrxTi1-x)O(3) ceramics with various compositions x in the range (0, 0.5), prepared via solid state reaction. The changes induced by the compositional-induced crossover ferroelectric-to-relaxor state are investigated by monitoring the changes of the FORC diagrams (the coercive and bias fields corresponding to the maximum, ratio of the reversible/irreversible contribution to the polarization, the diffuse character of the FORC distribution). The first derivative of the FORCs related to the tunability is a function of both the applied and reversal fields. The critical fields for the highest tunability were found to be composition-dependent
Impedance spectroscopy method for investigation of the polycrystalline inhomogeneous ceramics
Test of the Kolmogorov-Johnson-Mehl-Avrami picture of metastable decay in a model with microscopic dynamics
The Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory for the time evolution of
the order parameter in systems undergoing first-order phase transformations has
been extended by Sekimoto to the level of two-point correlation functions.
Here, this extended KJMA theory is applied to a kinetic Ising lattice-gas
model, in which the elementary kinetic processes act on microscopic length and
time scales. The theoretical framework is used to analyze data from extensive
Monte Carlo simulations. The theory is inherently a mesoscopic continuum
picture, and in principle it requires a large separation between the
microscopic scales and the mesoscopic scales characteristic of the evolving
two-phase structure. Nevertheless, we find excellent quantitative agreement
with the simulations in a large parameter regime, extending remarkably far
towards strong fields (large supersaturations) and correspondingly small
nucleation barriers. The original KJMA theory permits direct measurement of the
order parameter in the metastable phase, and using the extension to correlation
functions one can also perform separate measurements of the nucleation rate and
the average velocity of the convoluted interface between the metastable and
stable phase regions. The values obtained for all three quantities are verified
by other theoretical and computational methods. As these quantities are often
difficult to measure directly during a process of phase transformation, data
analysis using the extended KJMA theory may provide a useful experimental
alternative.Comment: RevTex, 21 pages including 14 ps figures. Submitted to Phys. Rev. B.
One misprint corrected in Eq.(C1
Spectral analysis of switching currents in doped barium titanate ceramics and nonlinear compensation
Ageing of low field dielectric constant and losses in (Hf, Zr)-doped
Ageing properties of weak field dielectric constant and losses of (Hf, Zr)-doped
\ab{BaTiO_3} ceramics in various crystalline phases are studied, and compared with
those of pure tetragonal \ab{BaTiO_3} ceramics. At room temperature, the ageing
process develops following two different mechanisms: a thermally activated
ageing process in pure tetragonal ceramics and a defects diffusion for the
doped ceramics. We consider that the main reason for the different ageing
mechanisms is the crystalline symmetry, which influences the twinning process
and the domain-wall dynamics. Our results prove that ageing of (Hf, Zr)-doped
\ab{BaTiO_3} ceramics depends on temperature by intermediate of the phase symmetry,
which imposes the twinning rate and rearrangement of ferroelectric domains
minimizing the elastic energy of the lattice
Raman investigation of the composition and temperature-induced phase transition in (1-x)Pb(Fe2/3W1/3)O3-xPbTiO3 ceramics
The evolution with temperature of the Raman activity in the (1 12x)Pb(Fe2 153W1 153)O3-xPbTiO3 solid solution with various compositions x 0a(0,\u20021) 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 153W1 153)O3 spectra showed a maximum of their intensity at 48500\u2002K. 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
Evidence of the relaxor-paraelectric phase transition in Pb(Fe2/3W1/3)O3 ceramics
The 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\u2013800 K. For high diffraction angles (160\ub0 and 162\ub0), a slight difference between the two phases was found. Raman spectra show an evolution with temperature with anomalies of bands of 848 cm 121 and 147 cm 121 (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
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