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The ω phase was initially thought to be a phase encountered only in group IV elements and its based alloys. Recent results, however, have shown that the formation of the phase is not confined to group IV but it is an ‘inbuilt transformation’ into a metallic system containing body centre cubic crystal structure. One of the least understood part of the β→ω transformation is the pre-transition effects associated with the transformation. The β→ω transformation shows pronounced pre-transition effects in terms of the appearance of diffuse intensity in diffraction patterns, phonon softening along certain wave vectors of the bcc lattice, anomalous diffusion, etc [1,2]. The appearance of diffuse scattering prior to the β→ω transition has prompted intense theoretical and experimental activities [1, 2]. One of the most noticeable features in the distribution of the diffuse intensity is shift in the maxima of diffuse intensity to incommensurate positions from the ideal ω position in the reciprocal space (Fig.1). Several models, in literature, have been proposed to predict the extent of the shift in the incommensurate positions of the diffuse maxima [3–5]. Most of these models, however, met with partial success. |
