Heat capacity calorimetry

Experimental heat capacity measurements of α-ZrW2O8, and zeolitic polymorphs of SiO2, BEA and MFI, have been made from 0.6 to 400 K. Measurements on β-ZrMo2O8 have been made from 8 to 400 K. Analysis of the results yields evidence for very low frequency modes in all four materials. These modes are responsible for negative thermal expansion behavior in α-ZrW2O8 and β-ZrMo2O8. Negative thermal expansion has been observed in some pure SiO2 zeolites, but no studies have been made to look for it in BEA and MFI. The appearance of low frequency modes in these two zeolites suggests that temperature dependent structural investigations would be worthwhile. These modes are lower in energy than the Boson peak in vitreous silica.