L. E. Cross

Connectivity and piezoelectric-pyroelectric composites

Connectivity is a critical parameter in composites designed for use as piezoelectric transducers or as pyroelectric detectors. There are ten important connectivity patterns in diphasic solids, ranging from a 0-0 unconnected checkerboard pattern to a 3-3 pattern in which both phases are three dimensionally self-connected. Processing methods for manufacturing some of these patterns are described. Series and parallel models for composite piezoelectrics and pyroelectrics lead to several interesting results, such as a diphasic pyroelectric in which neither phase is pyroelectric. The models are also helpful in interpreting the structure-property relations in single-phase materials where the crystal structures mimic certain connectivity patterns.

The Role of B-Site Cation Disorder in Diffuse Phase-Transition Behavior of Perovskite Ferroelectrics

In Pb(Sc0.5Ta0.5)O3 it has been shown that the degree of order in the B‐site Sc3+, Ta5+ cations can be controlled by suitable thermal annealing. For samples which have been well‐ordered by long annealing, dielectric measurements on single crystals show a normal first‐order ferroelectric phase change at 13 °C and a maximum low‐temperature spontaneous polarization of 23.0 μc/cm2. With increasing disorder, the crystals begin to exhibit the classical diffuse phase transition of a ferroelectric relaxor, with a broad Curie range and strong low‐frequency dielectric dispersion in the transition range. X‐ray diffraction measurements of the size of the ordered microregions suggest that ordering proceeds by different mechanisms in single‐crystal versus ceramic samples, though the resulting effects upon the dielectric behavior are very similar.

Origin of the High Piezoelectric Response in PbZr1-xTixO3

High resolution x-ray powder diffraction measurements on poled PbZr1-xTixO3 (PZT) ceramic samples close to the rhombohedral-tetragonal phase boundary (the so-called morphotropic phase boundary) have shown that for both rhombohedral and tetragonal compositions the piezoelectric elongation of the unit cell does not occur along the polar directions but along those directions associated with the monoclinic distortion. This work provides the first direct evidence for the origin of the very high piezoelectricity in PZT.

Tetragonal-to-monoclinic phase transition in a ferroelectric perovskite: The structure of PbZr0.52Ti0.48O3

The perovskitelike ferroelectric system PbZr1-xTixO3 (PZT) has a nearly vertical morphotropic phase boundary (MPB) around x=0.45–0.50. Recent synchrotron x-ray powder diffraction measurements have revealed a monoclinic phase between the previously established tetragonal and rhombohedral regions. In the present work we describe a Rietveld analysis of the detailed structure of the tetragonal and monoclinic PZT phases on a sample with x=0.48 for which the lattice parameters are, respectively, at=4.044 A, ct=4.138 A, at 325 K, and am=5.721 A, bm=5.708 A, cm=4.138 A, β=90.496°, at 20 K. In the tetragonal phase the shifts of the atoms along the polar [001] direction are similar to those in PbTiO3 but the refinement indicates that there are, in addition, local disordered shifts of the Pb atoms of ~0.2 A perpendicular to the polar axis. The monoclinic structure can be viewed as a condensation along one of the directions of the local displacements present in the tetragonal phase. It equally well corresponds to a freezing-out of the local displacements along one of the directions recently reported for rhombohedral PZT. The monoclinic structure therefore provides a microscopic picture of the MPB region in which one of the ‘‘locally’’ monoclinic phases in the ‘‘average’’ rhombohedral or tetragonal structures freezes out, and thus represents a bridge between these two phases.

Tetragonal-to-monoclinic phase transition in a ferroelectric perovskite

The perovskitelike ferroelectric system PbZr1-xTixO3 (PZT) has a nearly vertical morphotropic phase boundary (MPB) around x=0.45–0.50. Recent synchrotron x-ray powder diffraction measurements have revealed a monoclinic phase between the previously established tetragonal and rhombohedral regions. In the present work we describe a Rietveld analysis of the detailed structure of the tetragonal and monoclinic PZT phases on a sample with x=0.48 for which the lattice parameters are, respectively, at=4.044 A, ct=4.138 A, at 325 K, and am=5.721 A, bm=5.708 A, cm=4.138 A, β=90.496°, at 20 K. In the tetragonal phase the shifts of the atoms along the polar [001] direction are similar to those in PbTiO3 but the refinement indicates that there are, in addition, local disordered shifts of the Pb atoms of ~0.2 A perpendicular to the polar axis. The monoclinic structure can be viewed as a condensation along one of the directions of the local displacements present in the tetragonal phase. It equally well corresponds to a freezing-out of the local displacements along one of the directions recently reported for rhombohedral PZT. The monoclinic structure therefore provides a microscopic picture of the MPB region in which one of the ‘‘locally’’ monoclinic phases in the ‘‘average’’ rhombohedral or tetragonal structures freezes out, and thus represents a bridge between these two phases.

Direct evaluation of domain‐wall and intrinsic contributions to the dielectric and piezoelectric response and their temperature dependence on lead zirconate‐titanate ceramics

By making use of the fact that domain‐wall motions do not produce volumetric changes, an experimental method is introduced to directly and quantitatively determine the domain‐wall and intrinsic contributions to the piezoelectric and dielectric responses of a ferroelectric material. Utilizing this method, the contributions from the domain walls and intrinsic part as well as their temperature dependence for lead zirconate‐titanate (PZT) 52/48 and PZT‐500 ceramics are evaluated. The data show that at temperatures below 300 K, the large change in the dielectric and piezoelectric constants with temperature is due to the change in the domain‐wall activities in the materials. The results confirm that most of the dielectric and piezoelectric responses at room temperature for the materials studied is from the domain‐wall contributions. The data also indicate that in PZT‐500, both 180° wall and non‐180° walls are possibly active under a weak external driving field.

A monoclinic ferroelectric phase in the Pb(Zr1−xTix)O3 solid solution

A previously unreported ferroelectric phase has been discovered in a highly homogeneous sample of PbZr{sub 0.52}Ti{sub 0.48}O{sub 3} by high-resolution synchrotron x-ray powder diffraction measurements. At ambient temperature the sample has tetragonal symmetry (a{sub t} = 4.037 {angstrom}, c{sub t} = 4.138 {angstrom}), and transforms below {approx} 250 K into a phase which, unexpectedly, has monoclinic symmetry (a{sub m} = 5.717 {angstrom}, b{sub m} = 5.703 {angstrom}, c{sub m} = 4.143 {angstrom}, {beta}= 90.53{sup o}, at 20 K). The intensity data strongly indicate that the polar axis lies in the monoclinic ac plane close to the pseudocubic [111] direction, which would be an example of the species m3m(12)A2Fm predicted on symmetry grounds by Shuvalov.A previously unreported ferroelectric phase has been discovered in a highly homogeneous sample of PbZr{sub 0.52}Ti{sub 0.48}O{sub 3} by high-resolution synchrotron x-ray powder diffraction measurements. At ambient temperature the sample has tetragonal symmetry (a{sub t}=4.037{Angstrom}, c{sub t}=4.138{Angstrom}), and transforms below {approximately}250 K into a phase which, unexpectedly, has monoclinic symmetry (a{sub m}=5.717{Angstrom}, b{sub m}=5.703{Angstrom}, c{sub m}=4.143{Angstrom}, {beta}=90.53{degree}, at 20 K). The intensity data strongly indicate that the polar axis lies in the monoclinic {ital ac} plane close to the pseudocubic [111] direction, which would be an example of the species m3m(12)A2Fm predicted on symmetry grounds by Shuvalov. {copyright} {ital 1999 American Institute of Physics.}

Stability of the monoclinic phase in the ferroelectric perovskite PbZr1-xTixO3

Recent structural studies of ferroelectric

The Contribution of Structural Disorder to Diffuse Phase-Transitions in Ferroelectrics

{\mathrm{PbZr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}

Thermodynamic theory of PbTiO3

(PZT) with