Structural relaxation and evolution of free volume in metallic glasses
Structural studies in reciprocal and real space reveal a contrasting behavior between medium- (MRO) and short-range order (SRO). Structural relaxation is inhomogeneous: the free volume is not uniformly distributed across the atoms, varying significantly within the first atomic shell but remaining constant for the outer shells. In addition, annihilation of free volume (i.e. shrinking) during heating is observed in the MRO, whereas an increase of free volume (i.e. expansion) occurs in the SRO, implying a denser SRO in the as-prepared glass compared to the structurally relaxed material. This behavior is in agreement with the positive and negative density fluctuations related to the concepts of free volume and anti-free volume and can be attributed to the change of the coordination number in the first-nearest shell resulting from the reduction of the fraction of high-coordination polyhedra.
S. Scudino, M. Stoica, I. Kaban, K.G. Prashanth, G.B.M. Vaughan, J. Eckert: “Length scale-dependent structural relaxation in Zr57.5Ti7.5Nb5Cu12.5Ni10Al7.5 metallic glass”, Journal of Alloys and Compounds 639 (2015) 465-469 URL