Experimental visualization of oxide-ion diffusion paths in pyrochlore-type Yb₂Ti₂O₇

Abstract

Crystal structure and neutron scattering length density distribution of a pyrochlore-type ytterbium titanate Yb 2 Ti 2 O 7 have been investigated by in situ neutron powder diffraction measurements at 293 and 1173 K, Rietveld analysis and maximum-entropy method (MEM). In the MEM neutron scattering length density distributions of Yb 2 Ti 2 O 7 , the oxide ion O 48f bonding to Ti cation was relatively localized at lower temperature of 293 K, while it was largely distributed at a higher temperature of 1173 K. At 1173 K, one oxide-ion diffusion path along the ©110ª unshared edge of TiO 6 octahedron was clearly visualized and the other oxide-ion diffusion path along ©100ª, strictly ©2 ¹8x(O 48f ) + 3 8x(O 48f ) ¹ 3ª, shared edge of TiO 6 octahedron was also indicated. Here x(O 48f ) is the atomic coordinate x of O 48f anion. The MEM neutron scattering length density distribution and difference bond valence sum map at 1173 K strongly suggested that the energy barrier for oxide-ion migration along ©110ª directions was lower than that along the ©100ª one. Oxide ions three-dimensionally diffuse through both the ©110ª and ©100ª paths across the unit cell.

Enhanced Oxygen Ion Conductivity and Mechanistic Understanding in Ba3Nb1–xVxMoO8.5

“…48,49,50 The reliability of ionic conduction pathways obtained from bond-valence energy based methods has been confirmed by agreement with diffraction experiments and by results from maximum entropy studies and molecular dynamics calculations. 42,47,51,52 Furthermore, BVS methods have been effective in the screening and successful discovery of novel oxide ion conductors. 42,43,44,45 The low computational cost and reliability of the predicted relative migration energy barriers make softBV particularly useful for further investigation of the conduction pathways of inherently complex disordered crystal phases such as Ba3Nb1-xVxMoO8.5, for which density functional theory (DFT) calculations might be particularly challenging and computationally expensive.…”

The relationship between oxide-ion conductivity and cation vacancy order in the hybrid hexagonal perovskite Ba3VWO8.5

“…23,24 Bond-valence site energy (BVSE) calculations were employed to analyse the migration pathway and energy landscape of the oxide ion conduction in the average crystal structure of Ba 3 VWO 8.5 . Bond-valence based methods have been shown to reproduce well the ionic conduction pathway in several ionic conductors 17,[45][46][47][48][49][50] and have successfully been employed for the screening and discovery of new oxide ion conducting materials. [51][52][53][54] Despite being not as accurate, BVSE barriers generally show a good agreement with results from density functional theory (DFT) calculations.…”

Decoding ionic conductivity and reordering in cation-disordered pyrochlores

“…Interpreting the complex defect patterns in pyrochlores and related complex oxides [4,21,[27][28][29][30][31][32] from experiments is challenging. Atomistic simulations have long been used as a complementary approach for throwing light on fundamental defect properties and the attendant diffusional mechanisms.…”