The synthesis of chemically stabilized cristobalite (CSC) by a wet-chemical route is described. CSC is a form of silica (containing small amounts of other oxides) which is similar in many ways to P-cristobalite, but does not invert to acristobalite upon cooling. The effects of changing the dopant levels and various synthetic parameters on the phases formed in the Ca0-AIt03-Si02 system have been investigated. Stabilization of cristobalite with a number of different dopant combinations has been attempted, with mixed results. The use of wet-chemical techniques has led to the synthesis of apparently phase-pure CSC in a composition region where traditional solid-state synthetic techniques yield a mixture of other phases. [

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The phase stability and atomic-level compression mechanisms for both SiO2 cristobalite, and for cristobalite partially stabilized by Ca/Al doping (Cax/2 Si2−xAlxO4), have been investigated. A phase transition to a lower symmetry phase, observed with in situ high-pressure energy-dispersive x-ray diffraction, occurs at about 1.2 GPa. Structure models of the low-pressure phase were obtained by Rietveld analysis of neutron powder-diffraction data from powdered samples contained in a gas pressure apparatus. These data were collected at pressures up to 0.6 GPa and at 298 and 60 K. The results suggest collapse of the corner-connected framework from rotations of the rigid SiO4 tetrahedra at high pressures and low temperatures as the dominant mechanism for the densification of both materials. Compared to pure SiO2 cristobalite at the same pressure and temperature, the Ca/Al-doped material has a larger unit-cell volume. It also has a larger Si-O-Si bending angle and a more expanded framework as evidenced by the smaller rotations of the rigid SiO4 tetrahedra. The rate of change of these parameters as a function of pressure and temperature is the same for both pure and Ca/Al-doped cristobalite. These observations are consistent with Ca occupying positions within the cavities formed by the (Si, Al)-O framework and bracing it against collapse.