Elucidating hydrogen assisting vacancy formation in metals: Mo and Nb as examples

Abstract

Impurity H is inclined to be trapped by some defects with more space such as vacancy and grain boundary when it dissolves in a metal. Inversely, H can also enhance formation of large amount of vacancies even if there are few vacancies in intrinsic metals initially. Using first-principles simulation combined with statistical model, Mo and Nb as examples, we quantitatively calculate the concentration of vacancies including pure vacancy and H n -vacancy (H n V) complexes. The concentrations of vacancies in the form of H n V notably increase due to the decrease of effective formation energy of vacancy from H stimulation. Our finding solves a long-standing puzzle on the atomistic mechanism underlying H assisting vacancy formation in some metals.