Modeling Lattice Dynamics and Heat Capacities of Zeolites

Abstract

A theoretical study of the heat capacities of Quartz, zeolite MTT, and zeolite MFI is presented. The technique used to calculate the heat capacity can be applied to a many dielectrics, even those that are highly anisotropic, with complex crystal structures. For the aforementioned materials the assumptions used in Debye theory are too restrictive, the methodology presented in this paper uses a full set of dispersion relations obtained from atomistic simulation. Agreement with experiment for all materials studied is excellent, with the exceptions of temperature regions where phase transitions occur. The methodology that is used was developed with thermal conductivity in mind. It is hoped that this model will be smoothly incorporated into future conductivity models. Additionally, the effect of Al substitution on the heat capacity of MFI is investigated. It is predicted that aluminum substitution has a miniscule effect on the heat capacity of MFI.

Effects of nonframework metal cations and phonon scattering mechanisms on the thermal transport properties of polycrystalline zeolite LTA films

“…The present results on zeolite LTA are qualitatively similar to those obtained in zeolite MFI 36,41 and may be indicative of a more general thermal transport behavior in zeolites. The weak temperature dependence of the phonon scattering is also evident in molecular simulations preformed by Mc-Gaughey and Kaviany 11 on perfectly ordered siliceous LTA.…”

“…5. 43 The aforementioned materials are all composed of pure-silica frameworks. There are small but significant deviations between Qiu's data and our calculations.…”