PRESSURE-INDUCED PHASE TRANSFORMATIONS IN B1 AG-HALIDES

The structures which form with pressure from the Ag-halides in the B1-type have been investigated using X-ray powder diffraction techniques. It is proposed that AgCl transforms to a cinnabar (B9) type structure with c = 7.02 A ̊, a = 4.06 A ̊ and c a = 1.73 and a ΔV V0at the transition of 8 per cent. This structure is stabilized due to overlap of electron orbitals resulting in the formation of two highly covalent collinear-bonds. AgBr transforms to the same structure with a volume change of the same magnitude, but at a slightly lower pressure. The structure to which Bl-Agl transforms at 97 kbar is suggested to be tetragonal with a = 5.611 A ̊, c = 5.020 A ̊ with Δ V V0 at the transition approximately 13 per cent. Electrical conductivity measurements indicate that this transformation also involves a significant change to more covalent bonding. © 1969.