A lattice dynamics study of ZK-4 microporous material under different temperature and pressure conditions

The stability of zeolites is essential for their wide range of applications. Many experimental and theoretical studies have been focused on the stability of zeolites upon both high temperature and pressure conditions. The main objective of the present research was to compare the behavior of zeolite ZK-4 (with a LTA framework type) under a wide range of temperature and pressure conditions. Lattice Dynamics calculations were performed using the software package GULP. We have obtained the unit cell parameters, angles, bond distances and characteristic vibrational properties of zeolite ZK-4 in the range of 0 ≤ P ≤ 6 GPa and 0 ≤ T ≤ 1200 K. The unit cell volume decreased with a temperature increased as an evidence of a Negative Thermal Expansion process. The computational results suggested the strong structural disorder due to the application of the external pressure. Major distortions were present in T-O-T angles, followed by O-T-O angles and T-O distances. In general, comparative analysis based on our results shows that the effect of external pressure is more striking than that of temperature. Elastic constants and bulk moduli for heated and pressurized structures were obtained.