High-Pressure Phase Transition, Pore Collapse, and Amorphization in the Siliceous 1D Zeolite, TON

The siliceous zeolite TON with a 1-D pore system was studied at high pressure by X-ray diffraction, infrared spectroscopy, and DFT calculations. The behavior of this material was investigated using nonpenetrating pressure-transmitting media. Under these conditions, a phase transition from the <i>Cmc</i>2<sub>1</sub> to a <i>Pbn</i>2<sub>1</sub> structure occurs at close to 0.6 GPa with doubling of the primitive unit cell based on Rietveld refinements. The pores begin to collapse with a strong increase in their ellipticity. Upon decreasing the pressure below this value the initial structure was not recovered. DFT calculations indicate that the initial empty pore <i>Cmc</i>2<sub>1</sub> phase is dynamically unstable. Irreversible, progressive pressure-induced amorphization occurs upon further increases in pressure up to 21 GPa. These changes are confirmed in the mid- and far-infrared spectra by peak splitting at the <i>Cmc</i>2<sub>1</sub> to <i>Pbn</i>2<sub>1</sub> phase transition and strong peak broadening at high pressure due to amorphization.