Charlotte Malibert

Monoclinic structure of unpoled morphotropic high piezoelectric PMN-PT and PZN-PT compounds

Evidences of a monoclinic phase in unpoled (PbMg1/3Nb2/3O3)1-x-(PbTiO3)x with x=0.35 (PMN-PT 35%) and unpoled (PbZn1/3Nb2/3O3)1-x-(PbTiO3)x with x=0.09 (PZN-PT 9%) are presented from a neutron Rietveld analysis. This monoclinic phase is different from the phase recently evidenced by Noheda and coworkers in PbZr1-xTixO3 with x=0.481 but is identical to the phase observed in poled PZN-PT with x=0.102 by the same authors. The structural resolutions allowed us to compare both structures and to deduce the direction and magnitude of polarization. In PMN-PT 35% and PZN-PT 9% this phase is characterised by a weak value of polarization, a strong deformation of oxygen polyhedra and weak cationic shifts.

Order and disorder in the relaxor ferroelectric perovskite (PSN): comparison with simple perovskites and

We report a structural evolution analysis of the long-range and local order and disorder of lead scandium niobate (PSN) down to 10 K, using a combination of neutron and x-ray diffraction on powder and single crystals. The structure of PSN is discussed and compared with those of simple perovskite compounds and . In PSN the existence of a long-range but still disordered ferroelectric phase, different from those of simple perovskites, is evidenced. The disorder of lead and scandium/niobium atoms on short-, medium- and long-range scales is discussed in connection with the dielectric properties of these materials.

Combined theoretical and experimental study of the low-temperature properties of BaZrO{sub 3}

Low temperature properties of BaZrO3 are revealed by combining experimental techniques (X-ray diffraction, neutron scattering and dielectric measurements) with theoretical first-principles-based methods (total energy and linear response calculations within density functional theory, and effective Hamiltonian approaches incorporating/neglecting zero-point phonon vibrations). Unlike most of the perovskite systems, BaZrO3 does not undergo any (long-range-order) structural phase transition and thus remains cubic and paraelectric down to 2 K, even when neglecting zero-point phonon vibrations. On the other hand, these latter pure quantum effects lead to a negligible thermal dependency of the cubic lattice parameter below ~ 40 K. They also affect the dielectricity of BaZrO3 by inducing an overall saturation of the real part of the dielectric response, for temperatures below ~ 40 K. Two fine structures in the real part, as well as in the imaginary part, of dielectric response are further observed around 50-65 K and 15 K, respectively. Microscopic origins (e.g., unavoidable defects and oxygen octahedra rotation occurring at a local scale) of such anomalies are suggested. Finally, possible reasons for the facts that some of these dielectric anomalies have not been previously reported in the better studied KTaO3 and SrTiO3 incipient ferroelectrics are also discussed.

Anharmonicity and disorder in simple and complex perovskites: a high energy synchrotron and hot neutron diffraction study

We report a study of simple ABO3 type perovskites BaTiO3, PbTiO3, KNbO3, SrTiO3 and the relaxor perovskites PbSc1/2Nb1/2O3 (PSN) in their cubic phase using hard synchrotron radiation and hot neutrons. Gram-Charlier expansions of the thermal parameters have been performed and have revealed interesting features about the probability density function and the one-particle potential of the different atoms. This description is compared with other descriptions in terms of the split atom model and in terms of the rotator model. Structural trends regarding the order-disorder versus displacive character of the phase transitions have been obtained. It is concluded that SrTiO3 and BaTiO3 are quasi-harmonic systems whereas KNbO3 shows weak anharmonicity and PbTiO3 and PSN display strong anharmonic features.

Second-harmonic generation and x-ray diffraction studies of the pretransitional region and polar phase in relaxor K(1- x)LixTaO3

Optical second-harmonic generation (SHG) observations and precise x-ray diffraction experiments have been performed on quantum paraelectrics

Structural and dielectric characterizations of relaxor/ferroelectric superlattice films Pb(Sc1/2Nb1/2)O3/PbTiO3 fabricated on a single-lattice scale

\mathrm{K}\mathrm{Ta}{\mathrm{O}}_{3}

Microwave dielectric properties of the ordered and disordered Pb(Sc½Ta½)o3 ceramics

(KTO) and relaxors

Observation of Rotation of Polarization in Thin Films of Pb(Sc1/2Nb1/2)O3?PbTiO3 via a Monoclinic Phase

{\mathrm{K}}_{(1\ensuremath{-}x)}{\mathrm{Li}}_{x}\mathrm{Ta}{\mathrm{O}}_{3}

Temperature evolution of lattice strains in relaxor PbSc1∕2Nb1∕2O3 thin films

with

Syntheses of relaxor/ferroelectric superlattice thin films Pb(Sc1∕2Nb1∕2)O3∕PbTiO3 and their dielectric properties

x=3%