| INTRODUCTION
Chemical
routes to materials are based on transformations in solution such as sol-gel
processing, hydro or solvo thermal syntheses, Metal Organic Decomposition
(MOD), or in the vapour phase chemical vapor deposition (CVD). Most chemical
routes rely on the availability of appropriate “metal-organic” molecules as
precursors. The most obvious precursors for oxides are molecules having
already metal-oxygen bonds, namely metal alkoxides M(OR)n or
oxoalkoxides MO(OR)n (R = saturated or unsaturated organic group,
alkyl or aryl),
b-diketonates
M(b-dik)n
(b-dik
= RCOCHCOR') and metal carboxylates M(O2CR)n. The main
advantages of sol-gel techniques for the preparation of materials are low
temperature of processing, versatility, flexible rheology allowing easy
shaping and embedding. They offer unique opportunities for access to
organic-inorganic materials. The most commonly used precursors of oxides are
alkoxides due to their commercial availability and to the high lability of
the M-OR bond allowing facile tailoring in situ during processing.1,2
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