Jean-Michel Kiat

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.

Size effect in morphotropic phase boundary Pb(Mg1∕3Nb2∕3)O3–PbTiO3

Phases, domain configuration, and properties of 0.65Pb(Mg1∕3Nb2∕3)O3–0.35PbTiO3 ceramics with grain sizes of 4 and 0.15μm have been studied. The average phase is monoclinic Pm in coexistence with tetragonal. An evolution from micron-sized lamellar domains towards submicron/nanometer sized crosshatched domains is found with the decrease in size, which results in electrical relaxor type behavior and hindered switching. This is proposed to be associated with the slowing down of the relaxor to ferroelectric transition that causes the long time presence of an intermediate domain configuration. Nevertheless, a high sensitivity piezoelectric submicron-structured material is obtained under tailored poling (d33∼300pCN−1).

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.

Monoclinic morphotropic phase and grain size-induced polarization rotation in Pb(Mg1∕3Nb2∕3)O3–PbTiO3

A detailed Rietveld analysis of x-ray data, collected at room temperature, was done on ceramics with controlled grain size between 100nm and 4μm for (PbMg1∕3Nb2∕3O3)0.80–(PbTiO3)0.20 (PMN-PT20), i.e., a compound at the border of the so-called morphotropic phase boundary. With size reduction the polarization rotates within the monoclinic plane from MB, i.e., Px=Py>Pz to MA, i.e., Px=Py<Pz, and finally reaches a rhombohedral phase, i.e., Px=Py=Pz, below a critical value of ∼200nm without diminishing the amplitude of the polarization. This study provides an easy way to tailor the direction of polarization of these materials.

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

Rietveld refinement of the incommensurate structure of the elpasolite (ordered perovskite)

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

Rietveld analysis of strontium titanate in the Müller state

(KTO) and relaxors

Polar Order in Quantum Paraelectric SrTi16O3 and SrTi18O3 at Low Temperature

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

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

with