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

A thermal diffusion process of Ti into a LSTbO(3) substrate for optica l waveguides has generally been carried out under a wet gas atmosphere in order to prevent undesirable Li outdiffusion. In this work, such t hermal decomposition was confirmed to be significantly suppressed for an OH-free LiNbO3 substrate, even after a dry atmosphere annealing. No extra x-ray diffraction peak for LiNb3O8 was detected from the OH-fre e substrate after 10 h of annealing at 1000 degrees C in a dry O-2. Fu rthermore, the surface morphology of this sample, and as well an unann ealed one, were smooth. In a conventional LiNbO3 substrate containing many OH ions, subjected to a similar dry annealing, the presence of th e LiNb3O8 phase and a surface coarsening were observed.