Rafael Villaurrutia

Electron backscatter diffraction mapping of herringbone domain structures in tetragonal piezoelectrics

Herringbone domain structures have been mapped using electron backscatter diffraction in two tetragonal piezoelectrics: lead zirconate titanate [Pb(Zr,Ti)O3] and bismuth ferrite–lead titanate [(PbTi)0.5(BiFe)0.5O3]. Analysis of the domain misorientations across the band junctions shows that the structures correspond very well to crystallographic models. High resolution mapping with a 20nm step size allowed the crystal rotation across one of these band junctions in lead zirconate titanate to be studied in detail and allowed an improved estimation of the peak strain at the junction, of 0.56GPa. The significance of this for crack nucleation and propagation in such materials is discussed.

Domain structures and nanostructures in incommensurate antiferroelectric PbxLa1−x(Zr0.9Ti0.1)O3

The details of the domain structure of the incommensurate antiferroelectric structure in La-doped zirconium-rich lead zirconate titanate have been revealed in detail for the first time. The structure is dominated by 60° domain boundaries close to {101} planes of the primitive perovskite cell; and tilts of the perovskite sublattice of about 0.5° are also noted at such boundaries consistent with a small tetragonal distortion of the primitive cell. Within each domain a streaked nanostructure is revealed under weak diffraction conditions perpendicular to the long b-axis of the incommensurate supercell, which appears to be a consequence of planar faulting perpendicular to this b-axis. 90° domain boundaries are also observed but are less frequent than 60° boundaries and in contrast to previous reports, these often have rather curved and irregular boundary planes. The close similarity of all these features, with the one exception of the streaked nanostructure, to the domain structure of the commensurate antiferr...

Using EBSD and TEM-Kikuchi patterns to study local crystallography at the domain boundaries of lead zirconate titanate

Reliable EBSD mapping of 90° domains in a tetragonal ferroelectric perovskite has been achieved for the first time, together with reliable automated orientation determination from TEM‐Kikuchi patterns. This has been used to determine misorientation angles at 90° domain boundaries and thus local c/a ratios. The sources of orientation noise/error and their effects on the misorientation angle data have been thoroughly analyzed and it is found that this gives a cosine distribution of misorientation angles about the mean with a characteristic width related to the width of the orientation noise distribution. In most cases, a good agreement is found between local c/a ratios and global measurements by X‐ray diffraction, but some clear discrepancies have also been found suggesting that real local variations are present, perhaps as a consequence of compositional inhomogeneities.

Study of incommensurate phases in Lanthanum-doped zirconium-rich Lead Zirconate Titanate ceramics

The microstructure and nanostructure of zirconium-rich Pb(Zr,Ti)O3 ceramics doped with small amounts of La which are right at transition between the ferroelectric (FE) and antiferroelectric (AFE) orderings has been examined using Transmission Electron Microscopy (TEM) imaging and diffraction. In this region, the La doping frustrates the formation of simple FE or AFE phases and promotes long period ordered phases (2-3 nm) with ordering along with unit cells incommensurate with the primitive cubic unit cell. We show that the domain structure in these materials is closely related to that previously observed in AFE PbZrO3. Moreover, precision measurements of crystallographic tilts at domain boundaries using Kikuchi diffraction methods also confirms the close relationship to PbZrO3. The domains also contain a nanostructure perpendicular to the long-period ordering direction, but the reasons for the appearance of this nanostructure remain unclear.

Study of global and local crystallography at the domain boundaries of lead zirconate titanate piezoelectric ceramics

Reliable automated orientation mapping of 90° domains in a tetragonal perovskite has been achieved for the first time using both EBSD and TEM-Kikuchi pattern analysis. This has been used to compare local measurements of c/a ratios in PZT with global measurements by X-ray diffraction. The local c/a rations are in broad agreement with the global measurements, but further work is needed to determine whether the small discrepancies are real local variations or are caused by experimental factors.

EBSD studies of stress concentrations in ferroelectrics

The junctions between lamellar domain boundary structures in so-called “herringbone structures“ are expected to contain stress concentrations [1,2]. These herringbone domain junctions have been studied using electron backscatter diffraction to reveal crystallographic relationships across the domain boundaries and this data also reveals information about the localized stress concentrations at the junctions.

The influence of lanthanum doping on the structure of PbZr0.9Ti0.1O3 ceramics

Ferroelectric materials are widely used in applications ranging from piezoelectric through pyroelectric to electro-optic devices and further miniaturisation of ferroelectric devices, for instance in ferroelectric random access memories requires a better understanding of the nanostructure of these materials. Recently, we have shown that orientation mapping from diffraction allows the study of local crystallography and stress concentrations in tetragonal lead zirconate titanate (PZT) [1,2]. Nevertheless, rhombohedral PZT has been less studied, despite its commercial significance [3].