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06108 NICE

(France), S. PAROLA,

41296 Goeteborg (Sweden),

Technology,

S. JAGNER,

Chalmers

F. SOARES-CARVALHO,

University of

P. THOMAS,

J.P.

MERCURIO, URA 320, 87060 Limoges (France) ABSTRACT Several routes to mixed-metal Bi-Ti species have been investigated. The inertness of bismuth alkoxides Bi(OR) 3 (R = Et, iPr) toward their titanium analogs could be overcome by controlled microhydrolysis of Bi alkoxides. The first mixed-metal species based on bismuth, BiTi 2 0(OiPr)9 , has thus been isolated and structurally characterized. Coatings of Bi 4 Ti 3 OI 2 have been deposited on silicon wafers by using the gels derived from Ti and Bi 2-methoxyethoxides solutions. INTRODUCTION Although an increasing number of advanced oxide materials such as Bi 4 Ti 3 O1 2 , Bi 4 SrTi 4OI 5 , PbBi 2 Nb 2 O7

contain bismuth, sol-gel approaches remain limited and no

mixed-metal Bi-M "single-source" precursor has been reported so far. Bi 4 Ti 3 O1 2 is a ferroelectric with spontaneous polarization, it is thus a candidate for the ferroelectric layer of non volatile memory (RAM) [1]. The first chemical routes to it have been reported recently using either modified alkoxides [2,3] or alkoxides associated to acetates [4]. We report here the synthesis

and

characterization

of the

first

mixed-metal

Bi-Ti species,

namely

BiTi2 0(OiPr)9 as well as the elaboration and characteristics of Bi 4 Ti 3 OI 2 layers obtained by spin coating techniques using the gels derived from Ti and Bi 2-methoxyethoxides solutions. EXPERIMENTAL All reactions were conducted under inert atmosphere using Schlenk tubes and vacuum line techniques. Solvents were purified by standard techniques. Bi(OR) 3 (R = Et, iPr, tBu, C 2 H4 OMe) were prepared according to the literature [5] and Ti(OR) 4 (R

=

iPr, Et) (Aldrich)

were distilled before use. Infrared spectra were recorded on a IR-45S Bruker spectrometer as nujol mulls between KBr plates for the air-sensitive derivatives. NMR spectra were registred on solutions (Bruker AC-200 spectrometer). XRD patterns were obtained using a D 5000 Siemens 285 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society

diffractometer (CuI-jZ radiation) fitted out with a high temperature attachment Anton Parr HTK10 and a linear Elphyse detector. Thermogravimetric and differential thermal analyses were performed between 20 and 700"C by means of a Netsch STA 409 thermal analyser at a rate of 10*C mn-1. Micrographs were obtained

from a scanning electron microscope Philips

XL30 at 30 kV. RESULTS AND DISCUSSION Molecular constitution of the precursor solutions: synthesis and characterization of mixed-metal species

The mixing of homometallic alkoxides has traditionally been simplest route to the formation of mixed-metal

considered as the

species and thus to achievement of

homogeneity at a molecular level [6]. Bismuth alkoxides, Bi(OR) 3 (R = Et, iPr) remain insoluble in toluene in the presence

of Ti(OR) 4 ,

addition of the parent alcohol allowed

dissolution to occur, however no mixed-metal species are forme