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

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 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 < 110 > unshared edge of TiO6 octahedron was clearly visualized and the other oxide-ion diffusion path along < 100 >, strictly < 2 -8x(O-48f) + 3 8x(O-48f) - 3 >, shared edge of TiO6 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 < 110 > directions was lower than that along the < 100 > one. Oxide ions three-dimensionally diffuse through both the < 110 > and < 100 > paths across the unit cell. (C) 2018 The Ceramic Society of Japan. All rights reserved.