Daniel Phelan

Single Crystal Study of Competing Rhombohedral and Monoclinic Order in Lead Zirconate Titanate

Neutron diffraction data obtained on single crystals of PbZr(1-x)Ti(x)O3 with x=0.325 and x=0.460, which lie on the pseudorhombohedral side of the morphotropic phase boundary, suggest a coexistence of rhombohedral (R3m/R3c) and monoclinic (Cm) domains and that monoclinic order is enhanced by Ti substitution. A monoclinic phase with a doubled unit cell (Cc) is ruled out as the ground state.

Role of random electric fields in relaxors

Significance Relaxors are characterized by a frequency-dependent peak in the dielectric permittivity and are critical to modern technological applications because they exhibit large dielectric constants and unparalleled piezoelectric coefficients. Despite decades of study a fundamental understanding of the origin of relaxor behavior is lacking. Here we compare the structural, dynamical, dielectric, and piezoelectric properties of two highly similar piezoelectric lead-oxide materials: ferroelectric PbZr1–xTixO3 and relaxor Pb(Mg1/3Nb2/3)1–xTixO3. Random electric fields are implicated as the genesis of relaxor behavior, and the diffuse scattering associated with short-range polar order is identified as the order parameter. The piezoelectric response is found to be greatly amplified in crystals that display this diffuse scattering. PbZr1–xTixO3 (PZT) and Pb(Mg1/3Nb2/3)1–xTixO3 (PMN-xPT) are complex lead-oxide perovskites that display exceptional piezoelectric properties for pseudorhombohedral compositions near a tetragonal phase boundary. In PZT these compositions are ferroelectrics, but in PMN-xPT they are relaxors because the dielectric permittivity is frequency dependent and exhibits non-Arrhenius behavior. We show that the nanoscale structure unique to PMN-xPT and other lead-oxide perovskite relaxors is absent in PZT and correlates with a greater than 100% enhancement of the longitudinal piezoelectric coefficient in PMN-xPT relative to that in PZT. By comparing dielectric, structural, lattice dynamical, and piezoelectric measurements on PZT and PMN-xPT, two nearly identical compounds that represent weak and strong random electric field limits, we show that quenched (static) random fields establish the relaxor phase and identify the order parameter.

Neutron scattering measurements of the phonon density of states of FeSe 1 − x superconductors

Inelastic neutron-scattering experiments have been carried out on polycrystalline samples of the

Thermopower of Co-doped FeSe

{\text{FeSe}}_{1\ensuremath{-}x}

Phase diagram of the relaxor ferroelectric (1-x)Pb(Mg1/3Nb2/3)O3+xPbTiO3 revisited: A neutron powder diffraction study of the relaxor skin effect

superconductors. We report the phonon density of states for

Stacked charge stripes in the quasi-2D trilayer nickelate La4Ni3O8.

{\text{FeSe}}_{1\ensuremath{-}x}

Common origin of the two types of magnetic fluctuations in iron chalcogenides

with

Dissimilarity of polar displacements in barium and lead based relaxors

{T}_{c}\ensuremath{\approx}8\text{ }\text{K}

Nonlinear Pauli susceptibilities in Sr3Ru2O7 and universal features of itinerant metamagnetism

. The phonon cutoff frequency is observed around 40 meV. No significant change is observed across the superconducting transition. The measurements support the published first-principles calculations [A. Subedi et al., Phys. Rev. B 78, 134514 (2008)].

The relation of local order to material properties in relaxor ferroelectrics

The effect of cobalt doping on the thermopower of the superconductor FeSe is investigated through electrical and thermal transport measurements. Our results point to the destruction of superconductivity at very low Co concentrations. Thermopower data suggest negative charge carriers along with a large enhancement of the Seebeck coefficient, S, on the order of ≈−80 μV/K near T=100 K.