Volume Contraction at a Grain Boundary in Vanadium
  It is a conventional wisdom that symmetry breakdown at grain boundaries in crystals introduces volume expansion and there has been no confirmed evidence of volume contraction at a grain boundary in any kind of crystals. We report surprising volume contraction at the Sigma3(111) grain boundary in vanadium. The lattice distortion near this grain boundary is found to drive the local structure toward a hypothetical {\omega} phase, which is only slightly less stable than the bcc phase. Compressing lattice constant a of the {\omega}-phase down to the value of bcc, as is the case at the Sigma3(111) grain boundary, results in smaller c than in bcc structure, and hence the volume contraction. We also find such a volume contraction impedes the segregation of Ti and H, while enhances that of Cr, and hence a significant influence on material properties. The discovery adds fundamental new knowledge of condensed matter, and may also point to new techniques in grain boundary engineering of novel materials through volume control. 
Jin-Li Cao, Shigenobu Ogata, W. T. Geng
cond-mat.mtrl-sci