The effect of annealing atmosphere on structure characteristics of magnesium diffused lithium niobate single crystal substrates

MgO is evaporated on lithium niobate (LiNbO₃) single crystal substrates and is later annealed in air. The structure evolution of the MgO-rich layer as the Mg ion diffuses by means of annealing is investigated by conventional X-ray diffraction, glancing-incidence X-ray diffraction, and scanning electron microscopy. It is found that Li₃Mg₂NbO₆ and Mg₄Nb₂O₉ are first formed and followed by the formation of a uniform layer of Mg₄Nb₂O₉ in the MgO rich layer. Meanwhile, Li₃Mg₂NbO₆ is also formed in the MgO-rich subsurface layer. With the completeness of Mg-ion indiffusion, Li₃Mg₂NbO₆ and Mg₄Nb₂O₉ compounds disappear one after another, and LiNb₃O₈ finally appears in the diffused magnesium layer.