Far infrared microspectroscopy of zeolite MOR single crystal

Mordenite (structure type MOR) is one of nano-porous crystals of aluminosilicate zeolites. The framework of mordenite has one-dimensional channels along the c-axis. Cations, such as Na, are distributed at the side pockets of channels. We measured polarized far infrared absorption spectra of Na-type mordenite single crystals with the size of less than ∼100 μm. The measurements were performed by the microspectroscopy station of BL43IR at SPring-8. The polarization directions are set for parallel and perpendicular to the c-axis. The polarization dependence is observed clearly in the spectra. Absorption peaks are observed at 140 and 320 cm−1 for parallel polarization and at 170 and 280 cm−1 for perpendicular polarization. They are assigned to the anisotropic motion of Na cations and framework. The spectra are compared with the ordinary absorption spectra of the pellet forms of Na-, Rb- and H-type mordenite powders.