During low-temperature testing, new diffraction peaks that appear could be indicative of several phenomena. In one of our tests, we observed notable new peaks around 40° and 45° in a specific zeolite sample. We considered the possibility that these peaks were due to condensed ice crystals, but the XRD pattern of ice did not match these peaks well.
We also attempted to use GSAS refinement to simulate crystallographic changes in the 12-MR and 8-MR of the zeolite, but unfortunately, this did not match. Through the transformation of the d-spacing, we found that this should be a kind of small molecule cluster.
The testing process was conducted in situ. After removing the bulk water at high temperature under vacuum, the sample was vacuum-sealed and then cooled in situ.
Hongwei Chen
In small zeolite pores, a crystal lattice of ice can form, which in large pieces forms at high pressures. For comparison, you use an X-ray image of an ordinary crystal lattice, which we place in a glass to cool water. Therefore, look at X-ray images of other types of ice that form at high pressures. For orientation
O. Mishima, H.E. Stanley, Nature, 1998, 392, 12. https://doi.org/10.1038/32386
Water ice possesses many phases. At least three phases of amorphous water ice coexist in the initial sample at temperatures of 85–110 K -
Article Structural transitions in ice samples at low temperatures an...
Dear Hongwei Chen
These unidentified peaks can be searched for in a search-match programme such as PDF-5+ (https://www.icdd.com/pdf-5/) and Qualx2. Qualx2 (https://www.ba.ic.cnr.it/softwareic/qualx/) is free for academic use if you don't have access to the paid programmes.
Best regards
Analio Dugarte
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