A detailed study was made of He incorporation and diffusion in the perfect and

defective zircon lattices. Ab initio methods, based upon density functional theory,

were used to calculate structural features, solution energies in interstitial sites of

perfect zircon and vacancy sites of the defective lattice, plus the He diffusion

pathways. It was shown that the mode of He incorporation into perfect zircon was

influenced mainly by the topological features of the lattice. This promoted the site

preference of He towards accommodation in the interstitial sites present in the

middle of c-cylinder channels. The presence of defect species in the form of lattice

vacancies and interstitials had a marked effect upon He solubility and diffusivity in

the lattice, where the ability of lattice vacancies to act as physical traps or repulsive

sites depended greatly upon the electronic nature of the vacancy. The latter could

enhance the solubility of He in the lattice and affect the kinetics of He mobility in

the mineral.

He Incorporation and Diffusion Pathways in Pure and Defective Zircon ZrSiO4: a

Density Functional Theory Study. I.Saadoune, J.A.Purton, N.H. de Leeuw:

Chemical Geology, 2009, 258[3-4], 182-96