Author: Levine, Lyle Edward.
Title: ANALYTICAL ELECTRON MICROSCOPY OF QUASICRYSTALS.
Source: Dissertation Abstracts International. Volume: 51-08, Section: B, page: 3914.
Abstract: Although quasicrystals have been studied
intensely since their discovery in 1984, little is known about the underlying
atomic structure of these non-periodic phases. In this thesis, the local
atomic ordering of these phases is examined. Many analytical
electron microscopy techniques are used to obtain information
from quasicrystals and related crystal phases. Techniques employed
include selected area diffraction (SAD), convergent beam electron
diffraction (CBED), energy dispersive x-ray spectroscopy (EDS),
electron-energy-loss spectroscopy (EELS), high-resolution imaging,
and microdiffraction. Icosahedral phase Ti62Mn36Si2 was
transformed by annealing to produce three new crystalline phases.
SAD patterns from these phases show intensity modulations that closely
resemble the i-phase SAD patterns. Kikuchi bands from two of these crystal
phases have icosahedral symmetries. I present structural models based on
crystalline packings of icosahedral clusters of atoms that closely predict
the observed SAD modulations, the experimentally determined point groups,
the unit cell sizes, and the internal symmetries of these phases.
Localized diffuse scattering in reciprocal space is studied for two
i-phase alloys and two related complex crystal phases. Two existing
theoretical models, transition-state theory and the icosahedral glass,
are examined. A third model based on non-random disorder of atomic
positions within icosahedral clusters is presented. Finally, the
amorphous-icosahedral phase transition is studied using EELS. It is
shown that the local atomic order in amorphous Al75Cu15V10 and
Pd58.8U20.6Si20.6 are similar to that
in the respective i-phases. This similarity does not occur in the