ABSTRACT The thermal expansion of the host‐guest material, siliceous chabazite‐ N,N,N‐trimethyl‐1‐adamantyl ammonium, (CHA‐TMAda), obtained directly from hydrothermal synthesis, and calcined siliceous chabazite (CHA) were measured by variable‐temperature, high‐resolution, synchrotron, x‐ray powder diffraction. In contrast to the strong negative thermal expansion (NTE) found for chabazite, CHA‐TMAda exhibits isotropic zero thermal expansion (ZTE) with one of the lowest, measured, volume thermal expansion coefficients ( α v ) of 0.12(2) × 10 −5 K −1 from 120–394 K. This striking result is due to the presence of TMAda in the large chabazite cages of CHA and fluoride ions in the double six‐membered rings that strongly reduce transverse displacements of the oxygen atoms in the CHA framework, which are linked to the NTE mechanism in CHA. The use of selected organic structure directing agents, as in this case TMAda, for the hydrothermal synthesis of targeted zeolites provides a straightforward strategy to obtain a new class of host‐guest, nanostructured, crystalline ZTE materials made of light and abundant elements.
Campos et al. (Sun,) studied this question.