REDUCED THERMAL DECOMPOSITION OF OH-FREE LINBO3 SUBSTRATES EVEN IN A DRY GAS ATMOSPHERE

A thermal diffusion process of Ti into a LiNbO 3 substrate for optical waveguides has generally been carried out under a wet gas atmosphere in order to prevent undesirable Li outdiffusion. In this work, such thermal decomposition was confirmed to be significantly suppressed for an OH-free LiNbO 3 substrate, even after a dry atmosphere annealing. No extra x-ray diffraction peak for LiNb 3 O 8 was detected from the OH-free substrate after 10 h of annealing at 1000 °C in a dry O 2 . Furthermore, the surface morphology of this sample, and as well an unannealed one, were smooth. In a conventional LiNbO 3 substrate containing many OH ions, subjected to a similar dry annealing, the presence of the LiNb 3 O 8 phase and a surface coarsening were observed.