  (abridged) We present results of the disorder-induced
metal-insulator-transition (MIT) in three-dimensional amorphous indium-oxide
films. The amorphous version studied here differs from the one reported earlier
[PRB 46, 10917 (1992)] in that it has a much lower carrier concentration. As a
measure of the static disorder we use the dimensionless parameter kFl. Thermal
annealing is employed as the experimental handle to tune the disorder. On the
metallic side of the transition, the low temperature transport exhibits
weak-localization and electron-electron correlation effects characteristic of
disordered electronic systems. The MIT occurs at a kFl~0.3 for both versions of
the amorphous material. However, in contrast with the results obtained on the
electron-rich version of this system, no sign of superconductivity is seen down
to ~0.3K even for the most metallic sample used in the current study. This
demonstrates that using kFl as a disorder parameter for the
superconductor-insulator-transition (SIT) is an ill defined procedure. A
microstructural study of the films, employing high resolution chemical
analysis, gives evidence for spatial fluctuations of the stoichiometry. This
brings to light that, while the films are amorphous and show excellent
uniformity in transport measurements of macroscopic samples, they contain
compositional fluctuations that extend over mesoscopic scales. It is argued
that this compositional disorder may be the reason for the apparent violation
of the Ioffe-Regel criterion in the two versions of the amorphous indium-oxide.
However, more dramatic effects due to this disorder are expected when
superconductivity sets in, which are in fact consistent with the prominent
transport anomalies observed in the electron-rich version of indium-oxide. The
relevance of compositional disorder to other systems near their SIT is
discussed.
