Electronic structure and migration of interstitial hydrogen in the rutile phase of TiO₂

Abstract

The formation and migration energies of interstitial hydrogen in rutile TiO are obtained from first principles calculations. The computational approach was based on density functional theory with a semilocal generalised-gradient approximation functional, supplemented with an on-site Hubbard term to account for correlation among the Ti 3d electrons. Charge-transition levels are calculated and compared to previous theoretical studies. The donor character of hydrogen is examined in depth, focusing in particular on the tendency to form polaron-like configurations with the unpaired electron trapped at nearby titanium ions. Distinct minimum-energy paths of hydrogen migration and associated energy barriers were determined by the nudged elastic-band method. The present findings show clearly the strong anisotropy in the energy barriers for migration within the open c channels as opposed to migration crossing adjacent channels of the rutile lattice. For the rate-limiting step which leads to macroscopic diffusion along the c axis the corresponding rate and diffusion coefficient were also determined from transition-state theory. The results are discussed in connection to existing measurements of hydrogen diffusion and recent findings from electron paramagnetic resonance, electron-nuclear double resonance and muonium spectroscopies that probed the spatial localization of the electron spin.

Characterization and Reversible Migration of Subsurface Hydrogen on Rutile TiO2(110) by Atomic Force Microscopy at 78 K

“…It is pointed that KPFM can enable the direct measurement of the local contact potential difference (V LCPD ) at the atomic level, 31 and further theoretical calculation such as density functional theory is necessary to verify that if the local potential measurement by KPFM can reflect the charge distribution of the H sub species. 63 The local geometric configuration and electronic property of the H sub on rutile TiO 2 (110)-(1 × 1) have been systematically investigated and clearly clarified using the multichannel SPM measurement methodology in our study. Now, we extend our capability to deliberately manipulate the H sub by the SPM tip in a controllable manner.…”

“…The dumbbell-like configuration can still be observed, even with a different tip–sample distance (see Figure S6). It is pointed that KPFM can enable the direct measurement of the local contact potential difference ( V LCPD ) at the atomic level, and further theoretical calculation such as density functional theory is necessary to verify that if the local potential measurement by KPFM can reflect the charge distribution of the H sub species …”

Fast carrier diffusion via synergistic effects between lithium-ions and polarons in rutile TiO2

“…Most previous documents mentioned that the appropriate U value is between 4 eV and 6 eV for TiO 2 . [35][36][37][38][39] The simplified local spin density approximation GGA + U approach was used in our study, where the effective Hubbard term U = 5 eV and we checked that our main conclusions remain. The density functional theory calculations were performed by using the Vienna ab initio simulation package (VASP).…”

Understanding the magnetic dynamics and magnetostructural coupling in the paramagnetic phase ofTbMnO3by muon-spin spectroscopy

“…Muons were represented by the positively charged interstitial H + nuclei, since both of these particles are expected to have almost identical ground-state properties [31]. Although zero-point effects sometimes play a non-negligible role in the comparison of the ground-state properties of the proton and of the positive muon [32], in this case we are mostly concerned with the ground-state site, which is expected to be the same taking into account that the energy barriers around the site are usually larger than the zero-point energy corrections [33] The defect calculations were performed using an 80-atom supercell with fixed lattice parameters, doubled along the a-and b axes, with periodic boundary conditions. A 2 × 2 × 3 Monkhorst-Pack k-point mesh was chosen for the Brillouin-zone integrations, with ferromagnetic alignment of the Mn 3+ spins [34].…”