Fabien Remondiere

Electrical properties of (110) epitaxial lead-free ferroelectric Na0.5Bi0.5TiO3 thin films grown by pulsed laser deposition: Macroscopic and nanoscale data

We report the electrical properties, measured both at the macroscopic and nanometric scales, of epitaxial (110)-Na0.5Bi0.5TiO3 (NBT) thin films grown on (110)Pt/(110)SrTiO3 by pulsed laser deposition (PLD). The influence of the A-site composition (Na and/or Bi excess) on both the structural/microstructural characteristics and the electrical properties is discussed. Whatever the composition of the NBT target, the final layers are systematically epitaxially grown, with NBT crystallites mainly (110)-oriented, and as well (100)-oriented for some minor proportion. Atomic force microscopy (AFM) images reveal the coexistence of two kinds of grains presenting different shapes: namely flat and elongated grains, corresponding to (100)- and (110)-oriented NBT crystallites, respectively. The macroscopic ferroelectric properties were measured at room temperature. A rather well-defined shape of the hysteresis loops was obtained: the incorporation of a Bi excess in the target clearly improves the saturation of the loops...

Sol-gel synthesis of yttrium aluminum garnet (YAG): effects of the precursor nature and concentration on the crystallization

AbstractThe sol–gel synthesis of yttrium aluminum garnet (YAG) was performed using different metal precursors (salts and alkoxides of aluminum and yttrium) and metal concentrations (up to a concentration factor of 7.4). The cross-reactivity of the aluminum and yttrium precursors is not clear, and generally, the sol–gel process leads to polyphasic samples consisting of hexagonal YAlO3 and a monoclinic yttrium-aluminum oxide. Nevertheless, the high reactivity of the yttrium precursor can be offset by the use of an aluminum alkoxide and yttrium salt as the precursors, which results in the synthesis of pure-phase YAG at 1000 °C. The effects of the metal concentration in the sol–gel synthesis on the crystallite size of the resulting YAG are reported for the first time and are found to be significant with the crystallite size varying from 55 to 123 nm. Repeated experiments demonstrate that the proposed synthesis protocol is relatively robust. Effect of precursors on crystallization of YAG gel was studied and a pure YAG powder has been synthesized by a simple sol-gel process from yttrium chloride and aluminum butoxide. Influence of precursor concentration on crystallite size and SSA of YAG powder is reported for the first time.HighlightsPoly-cationic syntheses lead generally to polyphazed samples in Al2O3-Y2O3 diagram.Cross-reactivity of Al- and Y-precursors can be adjusted with an Al-alkoxide and an yttrium salt.YAG can successfully be synthetized by sol gel method from aluminum alkoxide and yttrium salt.Crystallite size increases significantly with precursor concentration.

Epitaxial growth and properties of lead-free ferroelectric Na 0.5 Bi 0.5 TiO 3 thin films grown by pulsed laser deposition on various single crystal substrates

The epitaxial growth of lead-free ferroelectric Na_0.5Bi_0.5TiO₃ (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.