Flexibility window controls pressure-induced phase transition in analcime

¹  Inorganic Chemistry Laboratory, University of Oxford - South Parks Road, Oxford OX1 3QR, UK, EU
²  Dipartimento Scienze della Terra, Università degli Studi di Milano - Via Botticelli 23, I-20133 Milano, Italy, EU
³  Department of Physics and Centre for Scientific Computing, University of Warwick - Gibbet Hill Road, Coventry CV4 7AL, UK, EU

Corresponding author: asel.sartbaeva@chem.ox.ac.uk

Received: 9 May 2008
Accepted: 5 June 2008

Abstract

Analcime under pressure undergoes a phase transition at ~ 1.0 GPa from a cubic form to a low-symmetry triclinic form. We use geometric simulation to relate the pressure behavior of analcime to a recently discovered property of zeolite frameworks, the “flexibility window”, defined as the range of densities over which the tetrahedral units in the framework can in principle be made geometrically ideal. Our results show that the range of stability of the cubic phase in analcime is defined by the flexibility window of the cubic framework. Analcime at low density can undergo tetragonal distortion while remaining within the flexibility window, consistent with experimental reports of non-cubic symmetries. On compression to higher densities, the capacity for tetragonal distortion is greatly reduced, accounting for the dramatic reduction in symmetry at the pressure-induced phase transition.