Diffraction Studies of a Highly Metastable Form of Amorphous Silica

An amorphous powder of SiO 2 that calorimetric studies indicated to be energetically metastable by 46.9 ± 0.8 kj/mol relative to fused silica was studied by X‐ray diffraction. A calculation of the energetic instability, based on the bond length and bond angle distributions derived from the diffraction data and utilizing the force constants for bond stretching and bending, indicated that 41.3 ± 7.9 kj/mol of the instability may be associated with distortions of the Si‐O bonds, the O‐Si‐O bond angles, and the Si‐O‐Si angles. Analyses of the extensive small‐angle scattering from the porous material suggested that only a small portion of the instability is associated with surface structures.