High Pressure Behavior of Mullite-Type Materials: Phase Transitions, Negative Linear Compressibility, Amorphization and Other Microstructural Implications
Even though mullite occurs rarely in natural rocks, it is perhaps one of the most important phases in both traditional and advanced ceramics and thus one of the most widely studied ceramic phases. Existing and emerging applications include: high temperature materials, aerospace materials, ballistic shielding components and even non-linear optical materials. There are many uncertainties regarding the basic physical properties of mullite-type materials, particularly in terms of their high-pressure phase stability and mechanical behavior that are important to address for new applications of mullites as an engineering materials. This work presents results of structural investigations of mullites and mullite-type materials at extreme pressures using synchrotron x-ray diffraction and laser Raman spectroscopy. The two experimental techniques used in this work are ideally suited to provide a synergical interplay in the study of mullites under high-pressure conditions: Raman spectroscopy is a technique for investigating short range order phenomena while x-ray diffraction accesses phenomena occurring at the long range order. Outcomes discussed include pressure-driven amorphization, phase transitions and negative linear compressibility.
