Controlling the Properties of Bulk Metal Oxides at a Molecular Level: Alkoxides Vs Carboxylates-Alkoxides Routes
- PDF / 382,562 Bytes
- 7 Pages / 414.72 x 648 pts Page_size
- 31 Downloads / 256 Views
LILIANE G. HUBERT-PFALZGRAF, STEPHANE DANIELE, SOUAD BOULMAAZ and RENEE PAPIERNIK, Universit6 de Nice Sophia-Antipolis, Parc Valrose, 06108 NICE C~dex 2, France ABSTRACT The reactions between alkoxides and/or alkoxides and anhydrous acetates have been investigated for access to advanced multicomponent niobates or titanates and with the aim to get insight into relationships between the nature of the initial precursors - single or mixedmetal derivatives, ligands (OAc or OR, R = Et, iPr),...- and the properties of the final material. Data are based on a variety of techniques: FT-IR, multinuclear NMR (IH, 13C, 207pb' 113Cd), X-ray investigations on single crystals. Powders have been analyzed by TGA, SEM-EDX, light scattering and XRD. INTRODUCTION Chemical routes to multicomponent oxides are generally based on the use of either metal alkoxides or of metal alkoxides associated to carboxylates [1]. Niobates, tantalates and titanates are largely involved as high-tech materials due to their attractive electrooptical, dielectric or piezoelectric properties [2,3]. We have thus investigated a large number of systems of type MZn-M'(OR)n, with Z =OAc or OR, M = Mg, Ba, Cd, Zn, Pb, n = 2; M' -
Nb, Ta, n'= 5; Ti, Zr n' = 4.
The various points adressed are - nature of the initial species: formation of mixed-metal species or not ?, their stoichiometry M:M' with respect of the formulation required for advanced materials, influence of the solvent, of the temperature of the reaction on the homogeneity at a molecular level - hydrolysis-condensation reactions : homogeneity of the final powders (segregation of the metals or not), elimination of the organics, temperature of crystallization. EXPERIMENTAL SECTION All manipulations were done under inert atmosphere using Schlenk tubes and vacuum line techniques. Anhydrous acetates were obtained by refluxing in acetic anhydride. Ti(OR) 4 (R= Et, iPr) were distilled before use, Nb(OR) 5 , [Zr(OiPr) 4 (iPrOH)] 2 , Ba(OiPr) 2 [4], Bi(OR) 3 [5] were obtained according to the literature. Spectroscopic characterization (IR, NMR) were performed as previously reported [5]. Thermogravimetric analysis was achieved under nitrogen on a Setaram system at a heating rate of 5°C/mn. X-ray powder diffraction patterns were collected with the CuK radiation.
21 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
RESULTS AND DISCUSSION Molecular constitution of the solutions of precursors The investigation of a large number of systems has been achieved. The results are summarized in schemes 1 and 2 for the M-Nb, M = Mg, Ba, Cd, Pb, Zn and Pb-M', M' Ti, Zr systems respectively.
1/2 M(OAc) 2 M=Cd, Pb, Mg
MNb 2(OAc) 2 (OiPr)lo 97 % A
/
N-T M =Pb (-AcOiPr)
Ba(OAC) 2
iPrO
M Mg, Cd
{
Nb(OiPr) 5 1/2 Pb(OAc) 2
Ba(OiPr) 2
I-AcOiPr)
[Zn(OiPr) 2]. BaNb 2 (OiPr) 12 (iPrOH) 2 95 %
A Pb 2 Nb 4O 5 (OAc) 2(OiPr)l 2 soluble
[
86 %
[ZnNb 2 0 2 (OiPr)8] 2 75 % Scheme I: Reactivity of Nb(OiPr) 5 toward alkoxides and acetates (Reactions in toluene and at room temperature if not otherwise stated) +
Data Loading...
