Precipitation kinetics of LiNbO₃ and LiNb₃O₈ crystalline phases in thermally annealed amorphous LiNbO₃ thin films

Abstract

The pyrochlore (LiNb 3 O 8 ) phase in lithium niobate crystal does not contribute to ferroelectric or electrooptic properties. We investigated a way to suppress the precipitation of this phase that was formed by thermally annealing amorphous LiNbO 3 films. The volume fraction of LiNb 3 O 8 with respect to LiNbO 3 becomes higher during longer annealing periods and at higher annealing temperatures because of the evaporation of Li 2 O units from the surface. Annealing in an O 2 atmosphere promotes the formation of the pyrochlore phase more than in a vacuum. We propose rapid thermal annealing of oxygen-rich LiNbO 3 film in a vacuum to provide the best solution to obtaining transparent, single LiNbO 3 phase film.

Room Temperature Ferromagnetism in Cobalt-Doped LiNbO3 Single Crystalline Films

“…This expression supports the notion that high P O 2 is beneficial to the formation of the LiNb 3 O 8 phase. The appearance of LiNb 3 O 8 in the high P O 2 of 20 Pa in our case is consistent with the previous work that the LN film annealed at the oxygen atmosphere at temperatures higher than 700 °C resulted in the precipitation of the LiNb 3 O 8 phase, and that rapid thermal annealing could produce transparent and single LN phase film. , …”

“…Therefore, the major challenge with the Co:LN growth is the control of the Li species transfer in the plasma from the target to the substrate. Because Li 3 NbO 4 and LiNb 3 O 8 phases do not contribute to ferroelectric or electro-optic properties, P O 2 should be severely controlled to obtain stoichiometric Li/Nb concentration and to grow single-phase Co:LN films.…”

“…The appearance of LiNb 3 O 8 in the high P O 2 of 20 Pa in our case is consistent with the previous work that the LN film annealed at the oxygen atmosphere at temperatures higher than 700 °C resulted in the precipitation of the LiNb 3 O 8 phase, and that rapid thermal annealing could produce transparent and single LN phase film. 14,17 Figure 2 presents the XRD pattern (between 2θ ) 30°and 100°) of the Co:LN film prepared in the P O 2 of 10 Pa, in which the two diffraction peaks observed around 38.98°and 81.72°a re characteristic of the R3c LN structure, the c-axis being perpendicular to the substrate plane. Very slow scans near the peaks of both hexagonal and cubic cobalt phases reveal no signatures of any kind of additional phases in the film.…”