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We report a systematic study that reveals the effect of composition ͑silicon-to-aluminum ratio͒ and the role of different phonon scattering processes on thermal transport in the nanoporous zeolite MFI. This is accomplished via synthesis of a series of films with graded compositions, thermal property measurements, and lattice dynamical modeling in the framework of the Boltzmann equation. MFI films with different Si/Al ratios ͑from infinity to 26͒ and constant ͑h0l͒ out-of-plane orientation were successfully synthesized by a seeded hydrothermal process. Three-omega measurements on these films allowed us to obtain comprehensive information on the thermal conductivity of MFI as a function of temperature ͑150-450 K͒ and Si/Al ratio. Detailed atomistic simulations ͑energy minimization and phonon dispersion calculations͒ were carried out for the MFI crystal structure with different Si/Al ratios and incorporated into a Boltzmann transport model along with approximate theoretical expressions for describing the rate of phonon scattering through umklapp, defect, and boundary scattering processes. The model predicts the observed thermal conductivity behavior very well across the entire range of temperature and composition investigated, with only a small number of fitting parameters of physical significance which allow us to distinguish the contributions of the different phonon scattering mechanisms. In particular, our results strongly suggest that the upper limit of thermal conductivity is defined by boundary-like scattering associated with the pore structure of the material. Below this limit, silicon substitution with aluminum allows considerable suppression of thermal conductivity by point defect scattering and a decrease in phonon velocity. These findings are important from the point of view of developing a robust platform for understanding thermal transport in complex crystalline materials with nanostructural features ͑such as an ordered nanopore network͒, which in turn serve as model systems for tuning of phonon transport properties in complex materials.

A study of the thermal properties of the zeolite MFI by a combination of experimental measurements and lattice dynamical modeling is presented. Thermal conductivity data in the range of 150-400 K was obtained through 3w measurements on polycrystalline zeolite films. While Debye theory is inadequate in predicting the zeolite thermal properties, a detailed calculation of the specific heat using a full set of dispersion relations obtained from atomistic simulations gives excellent agreement with experiments. In addition, the thermal conductivity is successfully reproduced by a phonon relaxation time-based model. The results indicate the possibility of developing a predictive model of the thermal properties of complex zeolite materials.