Structure of dehydrated zeolite Li-LSX by neutron diffraction: Evidence for a low-temperature orthorhombic faujasite

Li-LSX (Li-faujasite with Si/Al = 1), cubic at room temperature, is orthorhombic (Fddd) at 10 K. In the room-temperature Fd (3) over bar phase, Li cations in the supercage are evenly distributed between 2-fold-coordinated sites III and III', in close agreement with the cation distribution in Na-X, The cubic-orthorhombic phase transition implies extensive redistribution of strain through the lattice and displacement of Li cations, In the low-temperature Fddd phase the occupancy of sites II is reduced, and nearly half the Li cations are in the supercage, most of them in a new site III', midway between neighboring sites II.