On the origin of precipitation of transition metals implanted in MgO

Transition metals implanted in a stable oxide can either precipitate out at grain boundaries or can remain embedded in bulk. For MgO, experimentally it has been observed that some of the implanted Fe atoms precipitate out, while few Fe atoms in 2+ and 3+ charge states remain embedded in the lattice. Using first-principles calculations based on density functional theory, we show that formation energy, dopant site, barrier of transition and diffusivity, all these factors collectively determine the chance of precipitation of the implanted ion in the host lattice. Our calculations revealed that at 600 K (typical annealing temperature) while neutral iron in MgO would migrate 1 $$\mu $$ μ m in few microseconds, it takes several years for the charged Fe ions to migrate the same distance. On the other hand, Ni ions in all its charge states (neutral, 1+, 2+, and 3+) would migrate 1 $$\mu $$ μ m in just few microseconds, at 600 K. While explaining the experimentally observed precipitation of implanted Ni and few Fe atoms in MgO, this work provides a new scheme for predicting the stability of an implanted ion against precipitation in any stable rock-salt structured oxide. Graphic abstract