Effect of Very High Pressure on the Compressibilities of NH4Cl, TlCl, CdO, and CdS

Abstract

The effect of pressure to several hundred kilobars has been measured on the compressibilities of NH₄Cl, TlCl, CdO, and CdS. NH₄Cl and TlCl have the simple cubic (CsCl) structure at all pressures covered by this study. Our results for these compounds agree quite well with Bridgman's data to 98 kbar. The Born—Mayer equation fits NH₄Cl very well at all pressures. TlCl shows a lower compressibility than predicted by the B—M equation above about 150 kbar. CdO has the face‐centered‐cubic (NaCl) structure at all pressures. The B—M equation fits well up to 160 kbar, above which pressure CdO is less compressible than is predicted. CdS transforms from wurtzite to NaCl structure at 23 kbar. The compressibility of the high‐pressure phase is quite small and does not present a good test for ionicity by the B—M equation.