Disorder of Pb Atom in Cubic Structure of Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃ System

Abstract

The crystal structures of (1-x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 (PZN–PT: 0≤x≤0.3) in the cubic phase at 650 K have been investigated by analyzing the high-energy synchrotron-radiation (SR) powder diffraction data using the Rietveld method. It is found that the Pb atom does not settle at the ideal high-symmetry position with a harmonic thermal parameter. The split-atom method reveals that the Pb atom in the cubic phase is disordered and settles randomly at crystallographically equivalent positions slightly off-center of the cubic-corner site. The disordered directions of the Pb atom are significantly changed at the concentration x∼0.15. This structural boundary found in the cubic phase is related to the appearance of the morphotropic phase boundary (MPB).

Structural analysis of lead magnesium niobate using synchrotron powder X-ray diffraction and the Rietveld method

“…This indicates that there is a local site static disorder for Pb 2+ ions and O 2À ions from their ideal perovskite positions. Such behavior is observed in many Pb-based systems (Corker et al, 1998;Dkhil et al, 2001;Glazer et al, 2004;Kuroiwa et al, 2005;Terado et al, 2006;Singh & Tiwari, 2007;Zhang et al, 2011;etc. ) including in PMN (Bonneau et al, 1989(Bonneau et al, , 1991Verbaere et al, 1992;Thomas et al, 1999;Bhakar et al, 2013).…”

“…Although the split-atom approach does not give the true crystallographic structure, it has profound implications in disordered structures such as PMN. One advantage of the split atom approach is that one can fix the ADPs of atoms at a reasonable value and estimate static disorder (Bonneau et al, 1989(Bonneau et al, , 1991Corker et al, 1998;Dkhil et al, 2001;Glazer et al, 2004;Kuroiwa et al, 2005;Terado et al, 2006;Thomas et al, 1999). These static atomic shifts alter the intensity of the Bragg peaks and help in better fitting of diffraction data, which reflects in the reduction of the R-factors.…”

Use of bond-valence sums in modelling the diffuse scattering from PZN (PbZn1/3Nb2/3O3)

“…In particular, the atoms in the model presented here were all constrained to have displacive distributions (atomic displacement parameters, ADPs) consistent with previous results (Forrester et al, 2006;Terado et al, 2006). The data were collected at room temperature, and so on first inspection the correct structural model to use is that published by Forrester et al (2006).…”

“…There have been a number of high-quality powder diffraction studies of PZN (PbZn 1=3 Nb 2=3 O 3 ) (Forrester et al, 2006;Terado et al, 2006). However, the considerable detail available in the single-crystal diffuse scattering (SCDS), and its likely relation to the physical properties of the material, suggest very strongly that it is necessary to go beyond the average structure (Welberry et al, 2005;Xu et al, 2008;Burkovsky, Bronwald et al, 2012;Paściak et al, 2012;Paściak & Welberry, 2011).…”

Structure fluctuation in Gd- and Mg-substituted BaTiO3with cubic structure

“…A smaller t can also generate the antiferrodistortive thermal motion as observed in several perovskite-type oxides. [30][31][32][33] Although the Rietveld analysis derives only the average thermal motion, U O22 and t characteristics of seem to support the enhancement of the antiferrodistortive thermal motion in (Ba 1−x Gd x )(Ti 1−x=2 Mg x=2 )O 3 in the low-temperature and high-x regions. Here, the thermal behavior of the off-centered Gd ion is discussed in further detail.…”