Electron microscopic and diffraction study of proton-exchanged LiNbO₃

Abstract

The microstructure of proton-exchanged Li_1-xH_xNbO₃ (x = 1) is observed by high-resolution electron microscopy, single crystal electron diffraction and powder X-ray diffraction. Fully-exchanged HNbO₃, having perovskite-type structure (space group Pm3m; a = 3.822 Å), may be obtained from fine powders. For single crystal material, another cubic phase Li_1-xH_xNbO₃ is obtained, having a perovskite-related superstructure in space group Im3 (a = 7.645 Å). The structural basis for this phase and the atomic mechanism involved in the proton-exchange reaction may be understood using the concept of chemical twinning and octahedral tilting.