Tailored Molecular Precursors of Yttrium Oxide Using Functional Alcohols and Acetylacetone as Modifiers
- PDF / 324,409 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 53 Downloads / 162 Views
TAILORED MOLECULAR PRECURSORS OF YTTRIUM OXIDE USING FUNCTIONAL ALCOHOLS AND ACETYLACETONE AS MODIFIERS LILIANE
G.
HUBERT-PFALZGRAF*,
OLIVIER
PONCELET* AND
JEAN-CLAUDE
DARAN** *Laboratoire de Chimie Mol6culaire, Associ6 au CNRS, Universit6 de Nice-Sophia Antipolis, Parc Valrose, 06034 Nice, France **Laboratoire de Chimie des M6taux de Transition,
Place Jussieu, 75230 Paris, France
ABSTRACT Yttrium is involved as oxide in a variety of advanced materials.
Hydrolysis of its most
common alkoxide, yttrium oxoisopropoxide Y5 0(OiPr) 1 3 , is difficult to control as a result of the high electropositivity of the metal. Functional alcohols such as 2-methoxyethanol and acetylacetone have thus been used as modifiers.
These tailored precursors have been fully
characterized (single crystal X-Ray diffraction, IR, NMR. ). The tendency of methoxyethanol to act as a bridging ligand and to stabilize high oligomers - Y(OC 2 H4 OMe) 3 is a decamer - gives some insight into its behavior as "network builder". The unexpected cleavage of
acetylacetone
offers
a
route
to
an
interesting
acetatoacetylacetonate
derivative,
Y2 (OAc) 2 (acac) 4 (H2 0) 2 , but also suggest that this classical "modifier" could be affected by the hydrolysis-polycondensation reactions of the metallic species during the sol-gel process. Comparison of the hydrolysis behavior of the different precursors was performed. INTRODUCTION The importance of chemistry in the development of high performance ceramics is well established, and the sol-gel processing of glasses and ceramics has gained scientific as well as technological interest during the last decade [1]. Yttrium is involved as oxide in various materials such as yttrium-iron garnets (YIG), high Tc superconductors, fast sodium-ion conducting glass-ceramics (NASICON), and in the stabilization of thermomechanical ceramics [2].
Molecular precursors, especially metal alkoxides, are as versatile and thus attractive
precursors of oxides [3]. This paper reports the synthesis of yttrium oxoisopropoxide Y5 0(OiPr) 1 3 and of the 2methoxyethoxide
[Y(OC 2 H4 OMe) 3]1 0 ,
their
chemical
modification
in
the
presence
of
acetylacetone, and finally a comparison of their behavior towards hydrolysis. EXPERIMENTAL All syntheses were carried out under inert atmosphere, using Schlenk tube techniques. Spectroscopic characterization was done as published previously [4]. Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
74
Controlled Hydrolysis Hydrolysis of the different precursors was achieved in 0,05 M solutions in isopropanol or acetone.
Water was added as a solution in the same solvent.
Gelification was considered
achieved when the sample could be inverted. All experiments were performed in the same glass vessel and with the same total volume. RESULTS AND DISCUSSION Synthesis and Characterization of Precursors Among the various types of molecular precursors of oxide, metal alkoxides M(OR)n or oxoalkoxides MO(OR)n display attractive features [3] such as - high purity;
- ability
Data Loading...
