Caesium, compressibility

The Equation of State of the Alkali Halides.—The alkali halides, the fluorides, chlorides, bromides, and iodides of lithium, sodium, potassium, rubidium, and caesium have been more extensively studied experimentally than any other group of ionic crystals. For most of these materials, enough data are available to make a fairly satisfactory comparison between experiment and theory. The observations include the compressibility and its change with pressure, at room temperature, from which the quantities ai(T), o2(r) of Eq. (1.1), Chap. XIII, can be found... 

A study of RDX behaviour under static ultrahigh pressure (up to 65 GPa), generated by using diamond anvil cells (DACs) using FT-IR spectroscopy and UV-VIS absorption spectroscopy, is a topic of paper [61]. RDX changed its colour into dark red when compressed up to 20 GPa with caesium iodide (Csl), filled as a pressure medium. In this case the intensities of characteristics of IR absorption peaks of RDX decreased as the pressure increased, and did not return to the intensities measured at ambient pressure, after the pressure was unloaded. However, when RDX was compressed alone, its colour changed into yellow at a pressure above 60 GPa. In its UV-VIS absorption spectra the peak shifted from 243.5 nm at ambient pressure to 410 nm at 65.5 GPa. The authors assume that the HOMO-LUMO band gap of this nitramine decreases with increasing pressure [61] which is in line with the opinion of Kuklja and Kunz [59]. 

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