Ti K-edge XANES and Pb L_III-edge EXAFS studies of PbZr_0.40Ti_0.60O₃ferroelectric material

Abstract

Abstract. The structure of PbZr 0.40 Ti 0.60 O 3 crystalline ferroelectric material was studied by powder X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES) at Ti K-edge and Extended X-ray Absorption Fine Structure (EXAFS) at Pb L III -edge. The XRD Rietveld refinement shows a tetragonal crystal structure. The resulting crystal model was used to calculate both theoretical XAFS spectra. The mismatch beween experimental and calculated XAFS spectra is interpreted as a consequence of the random distribution of Ti and Zr. The resulting disorder effect is averaged in the long-range structure probed by XRD whereas the XAFS techniques probe the local order of each site. IntroductionLead zirconate titanate (PbZr 1-x Ti x O 3 ) is an alloy of lead titanate (PbTiO 3 ) and lead zirconate (PbZrO 3 ) which presents a perovskite structure (ABO 3 ). This system has been studied due to its interesting piezoelectric, pyroelectric, ferroelectric and dielectric properties [1]. Because of these characteristics, PbZr 1-x Ti x O 3 (PZT) system has been used in a great number of applications in many areas, such as hydrophones, thermal imaging, nonvolatile memories, surface acoustic wave generators, capacitors and gas sensors [1].The PZT system exhibits a cubic structure at higher temperatures and three different structures at room temperature depending on the composition: tetragonal, orthorhombic or rhombohedral. According to the proposed phase diagram [2], at the titanium-rich side all compositions present tetragonal structure with P4mm symmetry. On the other hand depending on the composition and the temperature, two rhombohedral phases, R3m and R3c, are known to occur in Zr-rich PZT ceramics.Most XAFS works of the PZT system involve Zr-rich compositions [3]. On the other hand, there are few works available in the literature about the short-range order structure of Ti-rich compositions [4,5]. The most complete studies of Ti rich PZT compounds [5] are essentially devoted to the XAFS study of amorphous compounds and thin films prepared by sol-gel methods. On the contrary, the aim of the present study is to characterize the local structure of the tetragonal ferroelectric PbZr 0.40 Ti 0.60 O 3 system, prepared by ball milling and calcination, using XAFS at Ti K-edge and Pb L III -edge and to compare these local structures with those obtained by powder XRD refinement.

Impact of Defect Structure on ’Bulk’ and Nano-Scale Ferroelectrics

“…It is noteworthy to say that the experimental results that we obtained are in very good agreement with the simulation of XANES spectra given in literature (37). Pb L3-edge XANES spectrum showed in Figure 4 the absorption features after the edge are related to the internal transitions between the 2p and the empty d states in Pb 2+ ions (37). Overall, as compared with the 'bulk' sample (500 nm), the 12 nm sample yields broadened spectral features, concerning pre-edge structures (A-D) and the post-edge (E-G) structures.…”

“…The pre-edge features labeled as C, E and F in the spectrum for the bulk ferroelectric do not appear in the spectrum for the nano-structured sample. It is noteworthy to say that the experimental results that we obtained are in very good agreement with the simulation of XANES spectra given in literature (37). Pb L3-edge XANES spectrum showed in Figure 4 the absorption features after the edge are related to the internal transitions between the 2p and the empty d states in Pb 2+ ions (37).…”

“…The corresponding XANES-spectra are shown in figure 4. The pre-edge features (labeled as A and B in figure 4) are atrributed to quadrupolar transitions of t 2g -type orbitals situated in the absorption Ti-atom (37). The transition A is caused by hybridization of p− and d-symmetry states at the Ti-atom under the influence of the neighboring oxygen atoms that takes place if the inversion symmetry is broken relative to the absorbing atom position (37).…”

“…The pre-edge features (labeled as A and B in figure 4) are atrributed to quadrupolar transitions of t 2g -type orbitals situated in the absorption Ti-atom (37). The transition A is caused by hybridization of p− and d-symmetry states at the Ti-atom under the influence of the neighboring oxygen atoms that takes place if the inversion symmetry is broken relative to the absorbing atom position (37). The pre-edge feature B is refered to the Ti 1s-electron transition to the unoccupied 3d-states of the neighbouring Ti-atoms and the transition occurs if there are 4d-atoms in the neighbourhood of the absorbing Ti-atom (37; 38).…”

Gamma attenuation through nano lead - nano copper PVC composites

“…In this effect the photon to deposit all its energy must do numerous scattering processes that its energy diminishes to lower than 200 keV where the probability to be absorbed by photoelectric effect is high, generally, the photon will be removed from the beam [5]. There is an important role in the interaction of photons inside the composite is the effect of K-edge where the Cu has a K-edge at 8.9 keV [26] and that for Pb at 88 keV [27]. 8 clarifies that composites loaded with nano lead oxide have the predominant effect on the attenuation of photons than those loaded with nano copper oxide especially in the energy region below 1 MeV but for higher energies, the values become closer.…”