Diffusion control of an ion by another in LiNbO₃ and LiTaO₃ crystals

Diffusion-doping is an effective, practical method to improve material properties and widen material application. Here, we demonstrate a new physical phenomenon: diffusion control of an ion by another in LiNbO₃ and LiTaO₃ crystals. We exemplify Ti⁴⁺/Xⁿ⁺ (Xⁿ⁺ = Sc³⁺, Zr⁴⁺, Er³⁺) co-diffusion in the widely studied LiNbO₃ and LiTaO₃ crystals. Some Ti⁴⁺/Xn⁺-co-doped LiNbO₃ and LiTaO₃ plates were prepared by co-diffusion of stacked Ti-metal and Er-metal (Sc₂O₃ or ZrO₂) films coated onto LiNbO₃ or LiTaO₃ substrates. The Ti⁴⁺/Xⁿ⁺-co-diffusion characteristics were studied by secondary ion mass spectrometry. In the Xⁿ⁺-only diffusion case, the Xⁿ⁺ diffuses considerably slower than the Ti⁴⁺. In the Ti⁴⁺/Xⁿ⁺ co-diffusion case, the faster Ti⁴⁺ controls the diffusion of the slower Xⁿ⁺. The Xⁿ⁺ diffusivity increases linearly with the initial Ti-metal thickness and the increase depends on the Xⁿ⁺ species. The phenomenon is ascribed to the generation of additional defects induced by the diffusion of faster Ti⁴⁺ ions, which favors and assists the subsequent diffusion of slower Xⁿ⁺ ion. For the diffusion system studied here, it can be utilized to substantially shorten device fabrication period, improve device performance and produce new materials.