Incommensurate modulated structure in the cubic-tetragonal transition of V-Ru alloys studied by high resolution electron microscopy

Abstract

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 〈0 1 1〉 positions in the electron diffraction patterns. This incommensurate structure is composed of many domains of the commensurate modulated structure with a pseudotetragonal cell of A=B=2(a 2 + c 2)1/2 and C=c, where a and c (∼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 〈0 1 1〉 directions with the approximate wavelength of 2√2a. We propose a model for the incommensurate modulated structure.