Abstract
In some alloys of Ti or Zr and certain transition metals a low-temperature, metastable, trigonal phase known as omega -phase is formed during quenching. For large solute concentrations, the Bragg reflections characteristic of the ideal omega -phase do not develop, but diffuse X-ray or neutron diffraction is observed at wavevectors close to (but not coincident with) these Bragg wavevectors. A simple one-dimensional model, inspired by previous calculations of charge-density-wave transitions, is proposed to explain the qualitative features of the diffraction observed for the diffuse omega -phase. This phase is viewed as an aggregate of domains of ideal omega -phase. Essential features of the model are the coherency of the domains and the restrictions placed on the phase relationships between neighbouring domains.