Hydrogen dynamics in indium oxide

It has been recognized that hydrogen is a shallow donor in several transparent oxides, including In$_{2}$O$_{3}$ [1]. Both interstitial H and H at an O vacancy have been suggested as candidates [2]. We have used the CRYSTAL06 code[3] with a hybridized DFT Hamiltonian to determine equilibrium positions and vibrational frequencies for both of these cases as well as for H at an In vacancy. While the bixbyite structure [4] of In$_{2}$O$_{3}$ has overall cubic symmetry, its remarkable internal asymmetries lead to a number of candidate locations for the H, each of which has different vibrational frequencies. This enables potential assignments of the experimental IR results obtained by Yin \textit{et al} [5]. Furthermore, the unique topology of In$_{2}$O$_{3}$ leads to constraints on possible H diffusion paths, which we have also investigated. \\[4pt] [1] P. D. C. King \textit{et al.}, Phys. Rev. B \textbf{80}, 081201(R) (2009).\\[0pt] [2] S. Limpijumnong \textit{et al.}, Phys. Rev. B \textbf{80}, 193202 (2009).\\[0pt] [3] R. Dovesi \textit{et al.}, \textit{Crystal06 User's Manual }(University of Torino, Torino, 2006). \\[0pt] [4] M. Marezio, Acta Crystallogr. \textbf{20}, 723 (1966).\\[0pt] [5] W. Yin \textit{et al.}, this meeting; M. Stavola \textit{et al.}, J. Appl. Phys. (to be published).