G. Shirane

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.

Phase diagram of the ferroelectric relaxor (1-x)PbMg1/3Nb2/3O3-xPbTiO3

Synchrotron x-ray powder diffraction measurements have been performed on unpoled ceramic samples of (1-x)Pb(Mg1/3Nb2/3)O32xPbTiO3 (PMN-xPT) with 30%≤x≤39% as a function of temperature around the morphotropic phase boundary, which is the line separating the rhombohedral and tetragonal phases in the phase diagram. The experiments have revealed very interesting features previously unknown in this or related systems. The sharp and well-defined diffraction profiles observed at high and intermediate temperatures in the cubic and tetragonal phases, respectively, are in contrast to the broad features encountered at low temperatures. These peculiar characteristics, which are associated with the monoclinic phase of MC-type previously reported, can only be interpreted as multiple coexisting structures with MC as the major component. An analysis of the diffraction profiles has allowed us to properly characterize the PMN-xPT phase diagram and to determine the stability region of the monoclinic phase, which extends from x=31% to x=37% at 20 K. The complex lansdcape of observed phases points to an energy balance between the different PMN-xPT phases which is intrinsically much more delicate than that of related systems such as PbZr1-xTixO3 or (1-x)Pb(Zn1/3Nb1/3)O32xPbTiO3. These observations are in good accord with an optical study of x=33%, where monoclinic domains with several different polar directions coexisting with rhombohedral domains, in the same single crystal, were observed.

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.

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

Polarization Rotation via a Monoclinic Phase in the Piezoelectric 92%PbZn1/3Nb2/3O3-8%PbTiO3

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

Universal phase diagram for high-piezoelectric Perovskite systems

(PZT) with

Phase diagram of the relaxor ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3

x=0.48,

Two spin-state transitions in LaCoO3

have revealed a monoclinic phase in the vicinity of the morphotropic phase boundary (MPB), previously regarded as the boundary separating the rhombohedral and tetragonal regions of the PZT phase diagram. In the present paper, the stability region of all three phases has been established from high-resolution synchrotron x-ray powder-diffraction measurements on a series of highly homogeneous samples with