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

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

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