Abstract
Binary NaCl and CsCl Wigner-Dyson lattices have been found to exhibit a new instability (mode-softening) at critical values of the charge ratio of the two species. These occur for transverse-acoustic vibrational modes with wave vector in the [110] direction in CsCl structure (and polarization in the [001] direction) at the first Brillouin-zone boundary and in the [100] direction in NaCl structure at the zone boundary (point for CsCl and point for NaCl in reciprocal-lattice space). These instabilities leave a gap in the charge-ratio parameter range in which the only currently known locally stable structure consists of segregated bcc lattices for the two species.
- Received 7 July 1980
DOI:https://doi.org/10.1103/PhysRevB.22.4992
©1980 American Physical Society