Hidden Chemical Order in Disordered Ba7Nb4MoO20 Revealed by Resonant X-Ray Diffraction and Solid-State NMR
Yasui, Yuta, Masataka Tansho, Kotaro Fujii, Yuichi Sakuda, Atsushi Goto, Shinobu Ohki, Yuuki Mogami, Takahiro Iijima, Shintaro Kobayashi, Shogo Kawaguchi, Keiichi Osaka, Kazutaka Ikeda, Toshiya Otomo, and Masatomo Yashima
The chemical order and disorder of solids have a decisive influence on the material properties. There are numerous materials exhibiting chemical order/disorder of atoms with similar X-ray atomic scattering factors and similar neutron scattering lengths. It is difficult to investigate such order/disorder hidden in the data obtained from conventional diffraction methods. Herein, we quantitatively determined the Mo/Nb order in the high ion conductor Ba7Nb4MoO20 by a technique combining resonant X-ray diffraction, solid-state nuclear magnetic resonance (NMR) and first-principle calculations. NMR provided direct evidence that Mo atoms occupy only the M2 site near the intrinsically oxygen-deficient ion-conducting layer. Resonant X-ray diffraction determined the occupancy factors of Mo atoms at the M2 and other sites to be 0.50 and 0.00, respectively. These findings provide a basis for the development of ion conductors. This combined technique would open a new avenue for in-depth investigation of the hidden chemical order/disorder in materials.