Person P. Neves

X-ray powder diffraction structural characterization of Pb1 − xBaxZr0.65Ti0.35O3 ceramic

The structure of Pb(1-x)Ba(x)Zr(0.65)Ti(0.35)O(3) (PBZT) ceramic materials with 0.00 < or = x < or = 0.40 was studied using synchrotron X-ray powder diffraction data. According to the Rietveld refinements, the structure of PBZT ceramics with x = 0.00, 0.10 and 0.20 at room temperature was rhombohedral R3c. A phase transition from rhombohedral to cubic was observed at 543 and 463 K for x = 0.10 and 0.20, respectively. The refinement for the compositions x = 0.30 and x = 0.40 showed a cubic structure from 10 to 450 K, in good agreement with the dielectric properties of these samples.

Structural Characterization of Pb1−xBaxZr0.65Ti0.35O3 Ferroelectric Ceramics

In this work, X-ray absorption near edge structure (XANES) and X-Ray Diffraction (XRD) have been used to characterize, respectively, the short and long range-order structure of Pb1− xBaxZr0.65Ti0.35O3 ceramics for 0.0 ≤ x ≤ 0.40. According to XRD-Rietveld refinements, a gradual rhombohedral to cubic like-phase transition occurs with increasing barium content. It is verified that the rhombohedral structural model fits well with the lower barium-content samples, while for the highest barium-content sample (x = 0.40) the fitting parameters obtained for the cubic phase is significantly better. The XANES measurements indicated that the local structure around Ti remains distorted for all barium concentrations, thus suggesting that the local structure of PBZT is weakly dependent on the crystallographic phase.

Experimental and Calculated Ti K-Edge XANES Spectra of Pb1-xLaxTiO3 Ferroelectric Ceramic Compounds

The X‐ray absorption near‐edge structures (XANES) at the Ti K‐edge of Pb1−xLaxTiO3 ferroelectric ceramic compounds are analyzed as a function of the sample composition. The calculated XANES spectra using the FEFF8.2 code are compared with experimental data. Experimental results show that the local distortion around Ti atoms has different composition dependence as compared to the crystallographic structure. Moreover, this distortion is also observed in samples presenting a crystallographically cubic phase. The agreement between experimental XANES spectra and theoretical ones deduced from the XRD results was good only for undoped and weakly doped samples. The use of structural models based on the XRD technique for samples containing higher amounts of lanthanum is not appropriate to describe correctly the local order around Ti atoms in this system.

Crossover from Ordinary Ferroelectric to Relaxor State: A Pre-Transitional Martensitic Transformation

In this work we have investigated the nature of the crossover from the ordinary ferroelectric to the relaxor state in (Pb 1 − x Ba x )(Zr 0.65 Ti 0.35 )O 3 ceramics through dielectric and structural characterizations. Based on the martensitic transformation concepts, it is proposed that the continuous addition of isovalent-ions in the normal ferroelectrics decreases the long-range elastic interaction, thus transforming the domain patterns from a micrometer polydomain structure, through single domains, to nanometer polar “tweed” structures with glasslike behavior, which are in turn strongly driven by defects. The electrical interaction between these weakly-coupled polar-tweed structures leads to a wide spectrum of relaxation times, thus resulting in a dielectric relaxation process.