Randomly organized and self-assembled Na0.5Bi0.5TiO3 nanodots elaborated by sol-gel and pulsed laser deposition routes

International audienceThis work reports for the first time on the elaboration, by both chemical (sol-gel) and physical (pulsed laser deposition) routes, of lead-free ferroelectric Na0.5Bi0.5TiO3 nanodots deposited on bare c-sapphire single crystal substrates presenting a 5° miscut angle along the [110] direction. Prior to any deposition, the sapphire substrates were treated at 1350 °C, during 24 h in air, in order to increase the height of the surface steps, reaching by this way ~8 nm. The experimental parameters adjusted for the growth of Na0.5Bi0.5TiO3 dots were the concentration of sols and the number of laser pulses (50 and 100) for the sol-gel and pulsed laser deposition routes, respectively. Whereas the sol-gel route leads to randomly organized Na0.5Bi0.5TiO3 nanodots in respect to the surface steps, the pulsed laser deposition route provokes the self-assembly for some important proportion of these dots along the same surface steps. Despite the lack of organization for the sol-gel dots, the latter present a much more regular distribution in size (~100 and ~10-20 nm as an average lateral dimensions and height, respectively) compared to dots deposited by laser ablation, where three different populations of grains can be observed. In each case, the dots do not seem to be epitaxially grown

Utilisation de la voie chimique pour le dépôt de films minces de matériaux ferroélectriques de structure perovskite

Les oxydes de structure perovskite Na0,5Bi0,5TiO3 (NBT) ou dérivés tels que les phases d'Aurivillius, MBi4Ti4O15 (M=Ba ou Sr) sont des candidats à l'élaboration de mémoires ferroélectriques non-volatiles exemptes de plomb. Le dépôt de films minces de MBi4Ti401S par décomposition d'organométalliques est étudié en fonction de la température de recuit, de la rampe de chauffe et de l'excès de bismuth introduit en excès dans le sol. Deux points sont mis en exergue : un effet de texture (00l)//(400)Si qui se justifie par l'anisotropie de la maille et l'utilisation d'une rampe de chauffe rapide RTA, un fort degré de texture est obtenu par l'ajout d'une couche de nucléation orientée à l'interface interne. Le procédé sol-gel appliqué à NBT a permis de cristalliser des films monophasés à basse température (T<500C) au sein desquels une activité piézoélectrique a été mise en évidence par - microscopie à force atomique (piézo-réponse). Des modifications sur le procédé sont réalisées.Perovskite based-oxides e.g. Na0,5Bi0,5TiO3 (NBT) or Bi-layered perovskites, called Aurivillius phases, MBi4Ti4O15 (M=Ba or Sr) are lead-free candidates for the fabrication of non- volatile ferroelectric memories. The chemical solution deposition of MBi4Ti4O15 thin films is studied as a function of annealing temperature, heating rate and bismuth exc.ess, contained into the sol. Two specific points are extracted : a texturation along (OOl)//(400)Sijustified by the anisotropy of the unit cell and the use of a rapid heating rate (RTA), a strong texture is obtained with the addition of an oriented seeding layer at the internaI interface. The sol-gel method applied to NBT system permits to crystallize single phase thin films at low temperature (T<500C). Such films are piezoelectric view to the atomic force microscope - (piezoresponse) analysis. Nevertheless some modifications have been undertaken.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

New lead-free perovskite compounds with (A1/2Bi1/2)(Mg1/3Nb2/3)O3 formula (A = Na,K)

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Fabrication of (Ba–Sr)Bi4Ti4O15 powders and thin films by metal organic solution routes

International audience(Sr,Ba)Bi4Ti4O15 powders were prepared by a metal organic decomposition (MOD) method. The thermal decomposition of the air-stable precursor solutions was studied using thermal analysis and X-ray diffraction (XRD). Thin films of (Sr,Ba)Bi4Ti4O15 have been deposited on Pt/TiO2/SiO2/Si substrates by spin-coating of the obtained precursor solutions. Phase formation, crystallite size and morphology of the thin films were investigated by X-ray diffraction and electron microscopy (EM). It is shown that monophasic (Sr,Ba)Bi4Ti4O15 phases with good crystallinity can be obtained in the form of thin films. Regarding the microstructure and the crystallographic orientation of the films, the role of the composition of the precursor solutions as well as the heating rate and the influence of the presence of a seeding layer on the platinum bottom electrode is discussed

Synthesis and crystallization pathway of Na0.5Bi0.5TiO3 thin film obtained by a modified sol-gel route

International audienceAs a lead-free candidate for electronic application, Na0.5Bi0.5TiO3 (NBT) thin films were produced by a 2-methoxyethanol sol–gel route and CSD method. Thermal decomposition and crystallization pathway of the alkoxide-based precursor have been studied by thermal analysis and X-ray diffraction (XRD) techniques. No transitory nanocrystalline phase was detected during the crystallization process of NBT. As a consequence, the nucleation of the stable perovskite phase occurred at low temperature (<500 ◦C). The parameters of the post-coating steps, i.e. drying and pyrolysis temperatures were chosen according to thermogravimetric data. Studies of the thermal annealing for crystallization are presented and discussed in terms of microstructure features from field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) observations

Study of the crystallization pathway of Na0.5Bi0.5TiO3 thin films obtained by chemical solution deposition

International audienceNa0.5Bi0.5TiO3 (NBT) thin films were fabricated by a chemical solution deposition (CSD) method. A route involving the reaction between sodium and bismuth acetates and titanium n-butoxide was used to synthesise the different precursor solutions. The thermal decomposition and crystallization pathways of different modified precursors have been studied by thermal analysis and X-ray diffraction techniques. As a consequence of the modification of the precursor solutions and their different thermal behaviour, the nucleation of the stable perovskite phase happens at different temperatures depending on each case but is found to be at temperatures as low as 500 degrees C. For the thin film processing, the drying and pyrolysis temperatures were chosen according to the thermogravimetric data to minimize the strain resulting from the shrinkage of the film during the elimination of solvents and organic ligands. The crystallization process was studied and the experimental results are discussed in terms of structural, microstructural and electrical features investigated by field-emission scanning electron microscopy, atomic force microscopy in tapping and piezo-force modes and X-ray diffraction

Non hydrolytic solvothermal synthesis and characterisation of metal oxide TiO2 or SnO2 nanoparticles

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Piezoforce microscopy study of lead-free perovskite Na0.5Bi0.5TiO3 thin films

International audienceAs a promising lead-free ferroelectric material, Na0.5Bi0.5TiO3 NBT was synthesized as thin films via a classic 2-methoxyethanol sol-gel route and chemical solution deposition method. Perovskite structure with random orientation of crystallites has been obtained on platinized silicon wafer at low temperature 460 °C. Piezoelectric activity in such films was detected using electrical analysis. X-ray diffraction and piezoresponse force microscopy PFM have been used to analyze NBT thin films with different microstructures and properties dependent on fabrication and annealing processes

Nonaqueous sol-gel synthesis and structural characterization of extra-small ZnO nanoparticles

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