Influence Of The Ti/Al Substitution On Ba/La Cationic Order In The Ba6-x-yLa8+2/3x+yTi18-yAlyO54 Solid Solution

The study of the Ba/La order in the Ba6-x-yLa8+2/3x+yTi18-y AlyO54 solid-solution was performed by X-ray diffraction on powders and single-crystals. The crystal structure of these phases belongs to the tetragonal tungsten bronze type, build on the basis of (3x3) TiO6 octahedron more than (2X2) (space group Pnma, a≈22.4Å, b≈7.7Å, c≈12.2Å). Two structural models were built, corresponding to two different orders within the structure. The model I, of formula [Ba4] A2 [Ba2-z La2x/3+y+q  q’ ]A1'[La8-q' q] A1Ti18-y AlyO54, corresponds to a model associated to infinite perovskite rows parallels to Oy axis, build on the basis of (3X3) TiO6 octahedron. The model II, with formula [Ba6-z z-2] A2 [La8+2x/3+y 2-(2x/3)-y] A1’A1Ti18-yAlyO54, can be described on the basis of three perovskite octahedron layers parallels to xOz plane.The study of the Ba/La order in the Ba6-x-yLa8+2/3x+yTi18-y AlyO54 solid-solution was performed by X-ray diffraction on powders and single-crystals. The crystal structure of these phases belongs to the tetragonal tungsten bronze type, build on the basis of (3x3) TiO6 octahedron more than (2X2) (space group Pnma, a≈22.4Å, b≈7.7Å, c≈12.2Å). Two structural models were built, corresponding to two different orders within the structure. The model I, of formula [Ba4] A2 [Ba2-z La2x/3+y+q  q’ ]A1'[La8-q' q] A1Ti18-y AlyO54, corresponds to a model associated to infinite perovskite rows parallels to Oy axis, build on the basis of (3X3) TiO6 octahedron. The model II, with formula [Ba6-z z-2] A2 [La8+2x/3+y 2-(2x/3)-y] A1’A1Ti18-yAlyO54, can be described on the basis of three perovskite octahedron layers parallels to xOz plane

MICROCRYSTALLINE CELLULOSE AS A GREEN WAY FOR SUBSTITUTING BaTiO 3 IN DIELECTRIC COMPOSITES AND IMPROVING THEIR DIELECTRIC PROPERTIES

International audienceBarium titanate (BT) and microcrystalline cellulose (MCC) were used to improve the dielectric properties of a commercial vinylic resin. Using a green method, two binary composites (vinylic resin/BaTiO 3 , vinylic resin/MCC) and one ternary composite (vinylic resin/BaTiO 3 /MCC) were prepared. The results obtained for the MCC containing composite show an identical evolution of the relative permittivity compared to BaTiO 3 composites with weak dielectric losses. In consequence, the feasibility of the substitution of BaTiO 3 with MCC, an economical and biosourced material is demonstrated

Epitaxial growth and properties of lead-free ferroelectric Na0.5Bi0.5TiO3 thin films grown by pulsed laser deposition on various single crystal substrates

International audienceThe epitaxial growth of lead-free ferroelectric Na0.5Bi0.5TiO3 (NBT) thin films on various single crystal substrates was successfully achieved, using the pulsed laser deposition technique (PLD). The present work is divided in two parts, focused on: (i) the growth of NBT layers on c- and r-sapphire (Al2O3) substrates, with and without introducing a CeO2 buffer layer, and (ii) the growth of NBT layers on bare (001)SrTiO3 substrates, with and without introducing a LaNiO3 layer, that could be used as a bottom electrode. In the first part, it was shown that the introduction of a CeO2 buffer layer completely modifies the out-of-plane growth orientation of the NBT films, as well as their microstructure. Indeed, (001)NBT films epitaxially grow only on r-Al2O3 substrates buffered with epitaxial (001)CeO2 layers, while, growing simply NBT on top of bare c or r-Al2O3 substrates, or on top of CeO2/c-Al2O3 heterostructures leads to polycrystalline or textured films. In the second part, we demonstrate that (001)-oriented NBT layers deposited on either bare (001)SrTiO3 or (001)SrTiO3 substrates (STO) covered with (001)LaNiO3 (LNO) are systematically epitaxially grown. Furthermore, the microstructure of the samples is strongly affected by the introduction of the LaNiO3 layer

Elaboration process of piezoelectric ceramics

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Na0.5Bi0.5TiO3 (NBT) and NBT based materials : modification of the dielectric properties by solid solutions formation

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Structure and properties of the lead-free perovskite compounds (Na1/2Bi1/2)ZrO3 (NBZ) and (K1/2Bi1/2)ZrO3 (KBZ)

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Structure and properties of Bi 2 Ti 2 O 7 pyrochlore type phase stabilized by lithium

International audienceA study of the Li2O - Bi2O3 - TiO2 ternary system evidenced a Bi2Ti2O7 pyrochlore phase in a large range of composition, centered on (Li1/2Bi1/2)TiO3 (LBT). This composition led to a pyrochlore phase stable up to 1100 °C, while pure Bi2Ti2O7 phase has been reported as metastable, with decomposition temperature around 600 °C. According to previous studies, this pyrochlore phase was not obtained without lithium and here only a few percent of lithium was necessary for stabilization. The structural study, performed by neutron diffraction, evidenced a cubic Fdm structure (a = 10.317 Å), similar to the one of “pure” Bi2Ti2O7 pyrochlore phase. The Li-ion is probably located on the Bi-site and is responsible for the stabilization of the pyrochlore structure. The electrical properties of the LBT composition were studied and appeared as very similar to the one of “pure” Bi2Ti2O7. Because of its large thermal stability range, this pyrochlore phase appears to be a promising material for dielectric or tunability applications