We utilize synchrotron X-ray diffraction measurements, conducted inside a diamond anvil cell, to analyze the high-pressure stability of Mg/Nb multilayered nanocomposites of equal (1:1) and unequal (1:10) thickness ratios. At larger layer thicknesses, Mg in these nanocomposites exists in its traditional hexagonal close packed (hcp) structure, while below a critical layer thickness of 7-8 nm, the Mg structure is found to transform into an interface strain-induced metastable pseudomorphic body center cubic (bcc) crystal structure. The hcp Mg present in the larger layer thicknesses exhibits an hcp-to-bcc phase transformation at pressures greater than 44 GPa, and this pressure value is found to vary between the equal and unequal Mg/Nb nanocomposite thickness ratios. On the other hand, the pseudomorphic bcc Mg structure is stable up to pressures of 60 GPa. Additionally, the compressibility of the pseudomorphic bcc Mg structure under pressure is shown to be fundamentally different from the bulk (nonlaminated) bcc Mg structure formed under high pressures. These results indicate that interface strain engineering, and an appropriate choice of the adjacent layer material, might be a viable pathway for tuning the structure and properties of the pseudomorphic bcc Mg structure.
Bibliographical noteFunding Information:
S.P. and M.J. acknowledge funding from the National Science Foundation (NSF) MRI No. 1726897 and NSF No. 1841331 for this work. I.J.B. acknowledges financial support from NSF CMMI No. 1729887. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Los Alamos National Laboratory, an affirmative action equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy under Contract No. DE-AC52-06NA25396. A portion of this work was performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA under Award No. DE-NA0001974, with partial instrumentation funding by the NSF. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. A part of this work was performed at the National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory. Molecular Foundry operations are supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
© 2019 Author(s).