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Intern: Jon Clements, UCSB
Mentor: Dr. Ashutosh Gandhi
Faculty Supervisor: Dr. Carlos Levi
Department: Materials |
STUDY OF THE EVOLUTION OF METASTABLE PHASES IN CHEMICALLY SYNTHESIZED Al2O3-Y2O3 AND Fe2O3-Y2O3 SYSTEMS
Metastable ceramic processing is a field of study that seeks to refine the desirable properties of ordinary ceramics by introducing metastability. If a system is in a metastable state, it is not at equilibrium and must overcome a thermodynamic barrier in order to reach the equilibrium state. Also, such materials are often nanocrystalline. Methods of non–equilibrium processing include rapid solidification processing, physical vapor deposition and chemical synthesis. Systems such as Yttrium Aluminum Garnet (Y3Al5O12, YAG) and Yttrium Iron Garnet (Y3Fe5O12, YIG), which have promising ceramic applications, have a tendency to form metastable phases under conditions which kinetically suppress the formation of the stable state. Using chemical synthesis, it is possible to produce metastable phases of YIG and YAG systems that can be quantitatively and qualitatively analyzed using X-ray diffraction (XRD). I was involved in using modified precursor spray pyrolysis, a method of chemical synthesis, to obtain homogeneous amorphous phases in the Al2O3-Y2O3 and Fe2O3-Y2O3 systems around the garnet composition. Homogeneity of the amorphous phase is necessary to ensure that we are studying the desired composition. If segregation is present, the composition can vary throughout the sample, making any formal analysis impossible. Having used precursor spray pyrolysis, upquenching and XRD, we concluded that precursor spray pyrolysis produces homogeneous amorphous phases for the Al2O3-Y2O3 system. However, for the Fe2O3-Y2O3 system we explored another method of chemical synthesis (co-precipitation) in order to produce a homogeneous amorphous phase. By finding homogeneity in the amorphous phase of Al2O3-Y2O3, it will be possible to study the phase evolution of the amorphous phase into the metastable phase.
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