Crystal Structure of AgI at 3 kbar

The nature of the atomic arrangement in the phase of AgI existing at pressures between 3 and 4 kbar has been deduced from x‐ray diffraction studies with a diamond‐anvil apparatus. The unit cell is either tetragonal or pseudotetragonal and contains a total of 4 atoms at $\text{000,}\frac{1}{2}\frac{1}{2}\text{0,}\frac{1}{2}\text{0z, 0}\frac{1}{2}\mathrm{z̄}$ with $\text{z\hspace{0.17em}=\hspace{0.17em}0.3}$ . The calculated density is 6.19 g/cm³. While it is not possible to determine directly the site preferences of Ag and I, certain distributions are suggested by a simple displacive mechanism of producing the 3‐kbar phase from the zincblende structure existing at room temperature and 1 atm pressure. The relationship of the new structure to that of the rock‐salt structure existing between 4 and 100 kbar is also discussed.