Orthorhombic distortion on Li intercalation in anatase

Abstract

The mechanism of the tetragonal-to-orthorhombic transformation upon Li-intercalation into anatase structured titania has been studied using first principle calculations. The primary mechanism for the formation of the orthorhombic phase is found to be the accommodation of donated charge in localized Ti-d yz orbitals leading to a cooperative Jahn-Teller-like distortion of the lattice. This model is examined further by considering electron addition states in pure anatase and the analogous structures of H 0.5 TiO 2 and Na 0.5 TiO 2 . It is shown that the rigid band model is not valid and population of the degenerate Ti-d xy,yz orbitals occurs beyond a critical concentration due to the repulsive interaction of the localized electrons. It is shown that the stability of the Li 0.5 TiO 2 structure is related to the similarity of the ionic radius of Li ϩ and Ti ϩ3 ions. Optimal configurations of H 0.5 TiO 2 and Na 0.5 TiO 2 are also predicted.

Defect Chemistry, Surface Structures, and Lithium Insertion in Anatase TiO2

“…These results provide no evidence that Li + migration is preferentially along the c axis, as in rutile, 42 or as suggested by Koudriachova et al for anatase. 58,59 The finding of a minimum energy octahedral site is consistent with experimental observations of Murphy et al 60 and Cava et al 61 who concluded, from neutron diffraction studies of the anatase to Li 0.5 TiO 2 phase transformation, that Li + ions reside on the octahedral sites, and this finding is broadly consistent with studies that identify two distinct sites for Li + occupation near the center of distorted oxygen octahedra. 62 A zigzag Li + migration path was also found by Lunell et al 63 using periodic Hartree-Fock calculations.…”

Observation of crystalline changes of titanium dioxide during lithium insertion by visible spectrum analysis

“…This reaction is a good example of our method because the electrochemical characteristics of TiO 2 highly depend on their structural parameters such as crystallinity and polymorphs. [11][12][13][14] This phenomenon is well interpreted by general ab initio principles and Maxwell's equations without any empirical limiting factors; therefore, we expect that our method can be applied to general types of materials and reactions.…”

GGA+Udescription of lithium intercalation into anataseTiO2

“…1͑a͔͒ shows no new features in the band gap, and the excess charge resulting from lithium intercalation occupies the bottom of the conduction band, as in previous calculations and in disagreement with the defect state observed in experimental XPS. 10,[50][51][52][53][54][55][56][57] The projected charge density associated with these occupied conduction band states is distributed over all the Ti atoms in the calculation; Fig. 2͑a͒.…”

“…[50][51][52][53][54][55][56][57] These studies report the excess electronic charge to be distributed over all the Ti atoms in the calculation, giving a metallic system with partial occupation of the bottom of the conduction band. These predictions of metallic behavior are incompatible with the localized defect state indicated by experimental photoabsorption 10 and disagree qualitatively with previous Hartree-Fock calculations.…”

“…[37][38][39][40][41][42][43][44][45][46][47] Previous theoretical studies of Li-intercalated TiO 2 have supported the transfer of charge to Ti sites. [48][49][50][51][52][53][54][55][56][57] The distribution of charge and corresponding electronic structure, however, depends strongly on the choice of theoretical method. Stashans et al employed Hartree-Fock to model Li intercalated rutile and anatase TiO 2 , and reported that the electron is transferred to the closest Ti atom to produce Ti 3+ , which gives rise to a defect peak in the band gap.…”