Morphotropic phase boundary and electrical properties of 1-x[Bi 0.5Na0.5]TiO3 -xBa[Zr0.25Ti 0.75]O3 lead-free piezoelectric ceramics

Lead-free solid solutions (1-x)Bi0.5Na0.5TiO 3 (BNT)-xBaZr0.25Ti0.75O3 (BZT) (x=0, 0.01, 0.03, 0.05, and 0.07) were prepared by the solid state reaction method. X-ray diffraction (XRD) and Rietveld refinement analyses of 1-x(BNT)-x(BZT) solid solution ceramic were employed to study the structure of these systems. A morphotropic phase boundary (MPB) between rhombohedral and cubic structures occured at the composition x=0.05. Raman spectroscopy exhibited a splitting of the (TO3) mode at x=0.05 and confirmed the presence of MPB region. Scanning electron microcopy (SEM) images showed a change in the grain shape with the increase of BZT into the BNT matrix lattice. The temperature dependent dielectric study showed a gradual increase in dielectric constant up to x=0.05 and then decrease with further increase in BZT content. Maximum coercive field, remanent polarization and high piezoelectric constant were observed at x=0.05. Both the structural and electrical properties show that the solid solution has an MPB around x=0.05. © 2012 Elsevier Ltd and Techna Group S.r.l.

Energy decay for the linear Klein-Gordon equation and boundary control

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

PROJECTIONS OF HYPERSURFACES IN R-4 WITH BOUNDARY TO PLANES

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A BOUNDARY ELEMENT FORMULATION FOR MASONRY WALLS: NON-LINEAR ANALYSIS

In this work, a non-linear Boundary Element Method (BEM) formulation with damage model is extended for numerical simulation of structural masonry walls in 2D stress analysis. The formulation is reoriented to analyse structural masonry, the component materials of which, clay bricks and mortar, are considered as damaged materials. Also considered are the internal variables and cell discretization of the domain. A damage model is used to represent the material behaviour and the domain discretization is also proposed and discussed. The paper presents the numerical parameters of the damage model for the material properties of the masonry components, clay bricks and mortar. Some examples are shown to validate the formulation.

Physical properties of self-polarized PZT thin films at compositions around the morphotropic phase boundary

The physical properties of self-polarized PbZr1-xTixO3 thin films with no preferential orientation in a range of compositions 0.46 <= x <= 0.50 were investigated. Structural analysis revealed the coexistence of monoclinic-tetragonal and monoclinic-rhombohedral phases at compositions 0.46 <= x <= 0.49, where the monoclinic phase was in the majority and both the tetragonal and the rhombohedral phases in the minority. The dielectric permittivity (epsilon'= 447) reached its maximum at around composition x = 0.48. Asymmetries in the macroscopic and local hysteresis loops confirmed the existence of the self-polarization effect in the studied films.

New features of the morphotropic phase boundary in the PbZrO 3-PbTiO3 system: A Raman spectroscopy study

In this work we present a Raman study of PbZr1-xTi xO3 ceramics with composition values close to the morphotropic phase boundary region. The analysis of the Raman spectra leads to the determination of the monoclinic phase extension at different temperatures in a very good agreement with those determined by diffraction techniques. Therefore the obtained results show that Raman spectroscopy is a powerful and suitable technique to study structural phase transitions in PbZr 1-xTixO3. © 2002 Taylor & Francis.

A geometric approach to cosmological boundary conditions

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The paramagnetic phase boundary of EuTe at low temperatures

Taking into account the presence of long-range dipolar interactions, we propose a model hamiltonian to calculate the canted-paramagnetic phase boundary of EuTe at low temperatures. By using spin-wave techniques we show that the critical field depends on T2 asymptotically. Our calculations are in good agreement with the experimental data. © 1981.

Características estruturais de aerogéis hidrofílicos e hidrofóbicos de sílica modificados com Dodecil Sulfato de Sódio

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