Ordered Defect Lattice in Lithium Niobate Crystals

Abstract

Nominally undoped and doped LiNbO₃ crystals have been studied using full-profile analysis of X‑ray diffraction data and Raman spectroscopy. The X-ray diffraction patterns and Raman spectra of the crystals contain weak superstructure lines forbidden for space group R3c. The observed superstructure lines are not reflections from a second phase. The intensity distribution and position of the additional reflections are essentially independent of nonstoichiometry and dopant concentration. The additional lines in the Raman spectra and X-ray diffraction patterns of the crystals can result from the formation of an ordered hexagonal defect superstructure sublattice with a doubled a cell parameter relative to the fundamental unit cell.