Symmetry-broken self-interstitial defects in chromium, molybdenum, and tungsten

Abstract

Since the nineteen-seventies, it was believed that the results of Huang x-ray diffuse scattering from radiation defects proved that a self-interstitial atom (SIA) defect in Mo adopted a $\ensuremath{\langle}110\ensuremath{\rangle}$ dumbbell configuration. However, resistivity recovery experiments performed using the same irradiated materials suggested a different, highly mobile, $\ensuremath{\langle}111\ensuremath{\rangle}$ SIA defect structure. Using density functional theory calculations, the authors have discovered that an SIA adopts a symmetry-broken $\ensuremath{\langle}11\ensuremath{\xi}\ensuremath{\rangle}$ configuration in chromium, molybdenum and tungsten, where $\ensuremath{\xi}$ is an irrational number. A $\ensuremath{\langle}11\ensuremath{\xi}\ensuremath{\rangle}$ defect migrates on average one-dimensionally through a sequence of three-dimensional nonplanar transitions, well correlated with the observed defect migration temperatures. Direct simulations of Huang diffuse scattering patterns from $\ensuremath{\langle}11\ensuremath{\xi}\ensuremath{\rangle}$ defect structures agree with observations, fully resolving the problem of the structure of defects in Mo and similar metals.