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 Yb2Ti2O7 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 Yb2Ti2O7, the oxide ion O48f 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 TiO6 octahedron was clearly visualized and the other oxide-ion diffusion path along ©100ª, strictly ©2 18x(O48f ) + 3 8x(O48f ) 1 3ª, shared edge of TiO6 octahedron was also indicated. Here x(O48f ) is the atomic coordinate x of O48f 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.