SEM characterization of micron-sized ErNbO4 precipitates induced in heavily-doped Er:LiNbO3 crystal by vapor transport equilibration

Abstract

X-, Y- and Z-cut congruently grown bulk Er(1.6, 2.0mol%):LiNbO3 crystals have been thermally treated using the vapor transport equilibration (VTE) technique. Optical absorption and X-ray powder diffraction measurements have been carried out to verify the existence of ErNbO4 precipitates induced by the VTE procedure in these crystals. Scanning electron microscope (SEM) has been used for the direct observation of crystallographic morphology of the ErNbO4 precipitates. The results show that the precipitates lie mainly in the (0001) crystallographic plane of the substrate and preferably grow with a crystallographic morphology of flat polyhedrons with rough dimensions of submicron×micron×micron. The precipitates on the surfaces of Z-cut substrates have only three orientations mutually aligned at approximately 60° or 120° angles being nearly parallel to the crystallographic axes of the host matrix. The SEM results show that VTE conditions and the type of crystallographic cut of the substrate remarkably affect the size and density of the precipitates.