Phase transformation and interface crystallography between TiO2 and different TinO2n−1 phases

Abstract

Magnéli phase titanium oxide (Ti_nO_2n−1, 4 ≤ n ≤ 10) has wide application prospects in energy storage, catalysis and other fields. During the preparation of the Ti_nO_2n−1 phase from TiO₂ by the carbothermal reduction reaction (CRR), the coexistence of multiple phases caused by the change in the reduction degree is the theoretical and practical basis for obtaining TiO₂/Ti_nO_2n−1 composite materials. In this work, the H₂Ti₃O₇ nanofiber has been employed as a precursor for the following CRR process. The X-ray diffraction (XRD), Raman spectroscopy, Thermogravimetric (TG) and Differential Scanning Calorimetry (DSC) analysis results confirmed the phase transformation process of H₂Ti₃O₇ → TiO₂(B) → anatase → rutile → Ti_nO_2n−1. Comprehensive transmission electron microscopy (TEM) characterization was carried out to investigate the phase composition and interface structures of the products calcinated at different temperatures. TiO₂/Ti₅O₉ and λ-Ti₃O₅/γ-Ti₃O₅ interfaces with specific orientation relationships have been observed. In addition, the phase transition mechanism has also been revealed based on the structural analysis results. By carefully considering the crystal structure and symmetry of the parent and new phase, the initial lattice strain matrix based on the two observed interfaces has been established accordingly. The crystallographic features of the two types of interfaces have been calculated based on modified invariant line theory, which has confirmed the consistency of the experimental observation and calculated results. The research in this paper can further expand the applicability of the three-dimensional invariant line theory in low symmetry crystal materials.