P. M. Gehring

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

Recently, a new orthorhombic phase has been discovered in the ferroelectric system (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-xPT) for x=9%, and for x=8% after the application of an electric field. In the present work, synchrotron x-ray measurements have been extended to higher concentrations 10%≤x≤15%. The orthorhombic phase was observed for x=10%, but, surprisingly, for x≥11% only a tetragonal phase was found down to 20 K. The orthorhombic phase thus exists only in a narrow concentration range with near-vertical phase boundaries on both sides. This orthorhombic symmetry (MC type) is in contrast to the monoclinic MA-type symmetry recently identified at low temperatures in the Pb(Zr1-xTix)O3 (PZT) system over a triangle-shaped region of the phase diagram in the range x=0.46–0.52. To further characterize this relaxor-type system, neutron inelastic scattering measurements have also been performed on a crystal of PZN-xPT with x=15%. The anomalous soft-phonon behavior (‘‘waterfall’’ effect) previously observed for x=0% and 8% is clearly observed for the 15% crystal, which indicates that the presence of polar nanoregions extends to large values of x.

X-ray and neutron diffraction investigations of the structural phase transformation sequence under electric field in 0.7Pb(Mg1∕3Nb2∕3)-0.3PbTiO3 crystal

The structural phase transformations of 0.7Pb(Mg1∕3Nb2∕3)O3-0.3PbTiO3 (PMN-30%PT) have been studied using x-ray diffraction (XRD) and neutron scattering as a function of temperature and electric field. We observe the phase transformational sequence (i) cubic (C)→ tetragonal (T)→ rhombohedral (R) in the zero-field-cooled (ZFC) condition; (ii) C→T→ monoclinic (MC)→ monoclinic (MA) in the field-cooled (FC) condition; and (iii) R→MA→MC→T with increasing field at fixed temperature beginning from the ZFC condition. Upon removal of the field, the MA phase is stable at room temperature in the FC condition, and also in the ZFC condition with increasing field. Several subtleties of our findings are discussed based on results from thermal expansion and dielectric measurements, including (i) the stability of the MA phase, (ii) a difference in lattice parameters between inside bulk and outside layer regions, and (iii) a difference in the phase transition temperature between XRD and dielectric data.The structural phase transformations of 0.7Pb(Mg1∕3Nb2∕3)O3-0.3PbTiO3 (PMN-30%PT) have been studied using x-ray diffraction (XRD) and neutron scattering as a function of temperature and electric field. We observe the phase transformational sequence (i) cubic (C)→ tetragonal (T)→ rhombohedral (R) in the zero-field-cooled (ZFC) condition; (ii) C→T→ monoclinic (MC)→ monoclinic (MA) in the field-cooled (FC) condition; and (iii) R→MA→MC→T with increasing field at fixed temperature beginning from the ZFC condition. Upon removal of the field, the MA phase is stable at room temperature in the FC condition, and also in the ZFC condition with increasing field. Several subtleties of our findings are discussed based on results from thermal expansion and dielectric measurements, including (i) the stability of the MA phase, (ii) a difference in lattice parameters between inside bulk and outside layer regions, and (iii) a difference in the phase transition temperature between XRD and dielectric data.

Phase instability induced by polar nanoregions in a relaxor ferroelectric system

Relaxor ferroelectrics are a special class of material that exhibit an enormous electromechanical response and are easily polarized with an external field. These properties make them attractive for applications as sensors and actuators. Local clusters of randomly oriented polarization, known as polar nanoregions (PNRs), are specific to relaxor ferroelectrics and play a key role in governing their dielectric properties. Here, we show through neutron inelastic scattering experiments that the PNRs can also significantly affect the structural properties of the relaxor ferroelectric Pb(Zn(1/3)Nb(2/3))O(3)-4.5%PbTiO(3) (PZN-4.5%PT). A strong interaction is found between the PNRs and the propagation of acoustic phonons. A comparison between acoustic phonons propagating along different directions reveals a large asymmetry in the lattice dynamics that is induced by the PNRs. We suggest that a phase instability induced by this PNR-phonon interaction may contribute to the ultrahigh piezoelectric response of this and related relaxor ferroelectric materials. Our results naturally explain the emergence of the various observed monoclinic phases in these systems.

Static magnetic correlations near the insulating-superconducting phase boundary in La2-xSrxCuO4

An elastic neutron scattering study has been performed on several single crystals of La

Neutron diffuse scattering from polar nanoregions in the relaxor Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3

_{2-x}

Soft Mode Dynamics above and below the Burns Temperature in the Relaxor Pb(Mg1/3Nb2/3)O3

Sr

Local Magnetic Order vs Superconductivity in a Layered Cuprate

_{x}

Ferroelectric ordering in the relaxor Pb(Mg1/3Nb2/3)O-3 as evidenced by low-temperature phonon anomalies

CuO

Soft phonon anomalies in the relaxor ferroelectric Pb(Zn(1/3)Nb(2/3))0.92Ti0.08O3

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Mode coupling and polar nanoregions in the relaxor ferroelectric Pb(Mg1/3Nb2/3)O-3

for {\it x} near the lower critical concentration {\it x