Mixed-Metal Bismuth-Titanium Species. Chemical Routes to Bi 4 Ti 3 O 12
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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
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