Cooperative Oxide-Ion Transport in Pyrochlore Y₂Ti₂O₇: A First-Principles Molecular Dynamics Study

Abstract

We developed a mapping approach for analyzing time-series data of local structural units based on the Voronoi–Dirichlet partition to quantify the defect states and oxide-ion migration mechanism in pyrochlore Y2Ti2O7 (space group: Fd3̅m) observed during first-principles molecular dynamics simulations. Defect states are classified into three types: a Frenkel pair, a single vacancy, and a split vacancy. Although the energetically most favorable defect type is a split vacancy at low temperatures, split and single vacancies are found to be equally favorable at high temperatures. Oxide-ion migration occurs by a two-step cooperative mechanism via a split vacancy. Climbing-image nudged elastic band calculations show the energy barrier for the cooperative diffusion mechanism (0.65 eV) to be substantially less than that of a simple stepwise mechanism (0.96 eV). This lower-energy barrier is comparable to experimental activation energies of oxide-ion diffusion in Y2Ti2O7 reported in the literature, making this previously unrecognized cooperative mechanism the most likely candidate for enabling oxide-ion transport in the titanate pyrochlore.

Tailoring Structural, Electronic, Optical, and Photocatalytic Properties of Y2Ti2O7 through a Passivated Codoping Approach

“…Yttrium titanate (Y 2 Ti 2 O 7 ) with a pyrochlore structure has been widely studied in recent decades due to its unique properties, such as thermal stability, large optical band gap, low phonon energy, high refractive index, excellent ion-electron conductivity, and high upconversion luminescence intensity in the visible wavelength. − Y 2 Ti 2 O 7 has a high symmetry with space group Fd 3̅ m . Y 3+ cations occupying the 16d site are surrounded by eight oxygen ions, while Ti 4+ cations occupying the 16c site are located in the center of the deformed octahedra.…”

Review —Recent Advances in Yttrium Titanate Pyrochlores: Crystal Structure and Impact of Doping Elements

“…It is a promising material for actinides immobilization, water-splitting reactions in photocatalysis, and florescent properties. [39][40][41][42][43][44][45][46][47] z E-mail: sciencepriya@gmail.com ECS Journal of Solid State Science and Technology, 2024 13 013012 This review consents to the recent developments and investigation properties centered on the Y 2 Ti 2 O 7 pyrochlore. The significant difference between doping elements and crystal structure on the various materials and its improved electrical, thermal, and optical properties for the various applications has been effectively analyzed.…”