Influence of short-range and long-range order on the evolution of the morphotropic phase boundary inPb(Zr1−xTix)

Abstract

The local structures of rhombohedral, monoclinic, and tetragonal phases across the morphotropic phase boundary (MPB) of Pb͑Zr 1−x Ti x ͒O 3 are discussed in terms of the progression from short-range to long-range and back to short-range structural order. It is shown that, provided one considers the structures on a suitably small length scale, all three phases can be considered to be monoclinic at the local level and that there need not be any discrete phase boundaries across the MPB. Electron diffraction experiments showing significant variations in diffuse streaking, illustrating the progression from short-range to long-range order, are presented in support of this model. It is suggested that it is the change in the range of structural order that plays the most important role in the increase in electrical and electromechanical properties around the MPB.

Influence of lanthanum doping on the morphotropic phase boundary of lead zirconate titanate

“…With the refinement of anisotropic displacement ellipsoids they showed, that disordered Pb cation displacement could still show a rhombohedral structure on average. This idea was extended by Glazer et al 9 to the tetragonal side across the MPB. They suggested that PZT follows a composition dependent progression from short range to long range and back to short range order by crossing the MPB.…”

“…2͑c͔͒ and the order parameters in Fig. 4 the theory of Glazer et al 9 could be considered: at the MPB the local ordering of Pb displacements is extended to long range order of a size sufficient that diffraction techniques see a distinct phase of monoclinic symmetry, which was reported by Schierholz et al for undoped PZT. 18,19 The domain structures in PLZT 54/46 have a size of several nanometers and the characteristics of a tetragonal microstructure but compared to PZT 13 no superordinated microdomain structures are visible.…”

“…They concluded that all of the three proposed regions of different structures of PZT, the tetragonal, the monoclinic, and the rhombohedral region could actually be described in terms of monoclinic order at a local level "provided one considers the structures on a suitably small length scale." 9 Despite extensive studies the structural properties of the MPB in these ferroelectric materials are still under discussion. Derived from Rietveld refinement of diffraction data using three-dimensional ͑3D͒ periodic structural models, some groups ͑Noheda et al 10 and Pandey et al 11 ͒ assume the structure to exist as a single monoclinic Cm phase in the area of the MPB, as R-values of the fit are lowest.…”

The missing boundary in the phase diagram of PbZr1−xTixO3

“…This was explained by displacing the Pb atoms away from the rhombohedral threefold axes to create local monoclinic structures 22 that averaged to an overall rhombohedral symmetry. On the basis of this assumption, Glazer et al 23 further proposed that the different average structures of PZT (R, M and T) could all be described in terms of local monoclinic ordering. Near the MPB region, the formation and the growth of these nanoscale regions may then account for the enhanced piezoactivity, in support of a domain-controlled contribution to the high piezoelectric properties 24,25 .…”

Electric-field-induced phase transformation at a lead-free morphotropic phase boundary: Case study in a 93%(Bi0.5Na0.5)TiO3–7% BaTiO3 piezoelectric ceramic

“…6,7 Finally, the prototypical MPB in this lead-based piezoelectric material is described not as a sharp border, with all three phases providing a monoclinic distortion. 8 Although the issue is not clearly settled, MPBs are being sought as a starting point for identifying lead-free piezoceramics. 4,9 For example, the solid solution of ͑1−x͒Bi 0.5 Na 0.5 TiO 3 -xBaTiO 3 has been shown to exhibit useful piezoelectric properties at compositions near x = 0.06-0.07.…”