Observation of Fundamental Mechanisms in Compression-Induced Phase Transformations Using Ultrafast X-ray Diffraction

• DOI: 10.1007/s11837-020-04535-4
• Publication Date: 2021-01-13T13:02:32Z
• Authors: Michael R. Armstrong; Harry B. Radousky; Ryan A. Austin; Elissaios Stavrou; Hongxiang Zong; Graeme J. Ackland; Shaughnessy Brown; Jonathan C. Crowh...; Arianna E. Gleason; Eduardo Granados; Paulius Grivickas; Nicholas Holtgrewe; Hae Ja Lee; Tian T. Li; Sergey Lobanov; Joseph T. McKeown; Bob Nagler; Inhyuk Nam; Art J. Nelson; Vitali Prakapenka; Clemens Prescher; John D. Roehling; Nick E. Teslich; Peter Walter; Alexander F. Gonc...; Jonathan L. Belof
• Keywords: Metastability; Picosecond; Nanosecond

As theoretically hypothesized for several decades in group IV transition metals, we have discovered a dynamically stabilized body-centered cubic (bcc) intermediate state in Zr under uniaxial loading at sub-nanosecond timescales. Under ultrafast shock wave compression, rather than the transformation from α-Zr to the more disordered hex-3 equilibrium ω-Zr phase, in its place we find the formation of a previously unobserved nonequilibrium bcc metastable intermediate. We probe the compression-induced phase transition pathway in zirconium using time-resolved sub-picosecond x-ray diffraction analysis at the Linac Coherent Light Source. We also present molecular dynamics simulations using a potential derived from first-principles methods which independently predict this intermediate phase under ultrafast shock conditions. In contrast with experiments on longer timescale (> 10 ns) where the phase diagram alone is an adequate predictor of the crystalline structure of a material, our recent study highlights the importance of metastability and time dependence in the kinetics of phase transformations.