A study on magnesium diffusion into LiNbO₃ single crystal by x-ray diffraction, differential thermal analysis, and scanning electron microscopy

The diffusion of magnesium into lithium niobate single crystal under different diffusion conditions has been studied by x-ray diffraction, glancing-incidence x-ray diffraction, differential thermal analysis, and scanning electron microscopy in an attempt to determine the diffusion mechanism and evaluate the crystallinily of the diffused layer. It is found that the magnesium diffused layer exhibits the crystal structure of an unknown compound from the Mg-Li-Nb-O ternary system and MgNb₂O₆. The MgNb₂O₆, is in the surface layer of the magnesium diffused layer, while the unknown compound is in the subsurface layer beneath the MgNh₂O₆. It is proposed that this unknown compound and MgNb₂O₆ which form during a solid state reaction between a thin layer of MgO and a lithium niobate crystal in a Li₂O-rich atmosphere are the real sources for Mg ion indiffusion into lithium niobate crystal. The changes in Curie temperature with diffusion parameters arc noted. Reasons of lattice distortion and mechanisms of Mg ion indiffusion are discussed and analyzed.