INCOMMENSURATE MODULATED STRUCTURE IN THE CUBIC TETRAGONAL TRANSITION OF V-RU ALLOYS STUDIED BY HIGH-RESOLUTION ELECTRON-MICROSCOPY

The cubic-tetragonal transition of V-Ru alloys near 50 at % has been investigated by high resolution transmission electron microscopy. In the cubic to tetragonal transition process of thin foil specimens, we found an incommensurate modulated structure showing satellite spots near 1/4 <011> positions in the electron diffraction patterns. This incommensurate structure is composed of many domains of the commensurate modulated structure with a pseudo-tetragonal cell of A = B = 2(a2 + c2)1/2 and C = c, where a and c (congruent-to 1.07a) are the lattice constants of the tetragonally distorted CsCl-type structure. The modulation is interpreted in terms of the combination of dual elastic shear distortion waves nearly parallel to the <011> directions with the approximate wavelength of 2 square-root 2a. We propose a model for the incommensurate modulated structure.