Effect of High Pressures on the Compressibilities of Seven Crystals Having the NaCl or CsCl Structure

The effect of pressure to several hundred kilobars has been measured on the compressibilities of seven substances having the NaCl (fcc) or CsCl (sc) structure. These include NaCl, KCl, CsCl, MgO, CaO, CaS, and TlI. For the first four crystals a Born—Mayer treatment involving the Madelung energy, van der Waals' terms, and an exponential repulsion (with constants evaluated from initial volume and compressibility) gave a quantitative fit throughout the range. CaO has a measurable lower compressibility at high pressure than predicted from the theory. This effect is exaggerated in CaS. An interesting feature of the behavior of TlI is that although it exhibits metallic conductivity above 160 kbar, there is no measurable discontinuity in the compressibility near this point.

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