absorption spectra of pure lithium niobate crystals

The absorption spectra of congruent pure and nearly stoichiometric lithium niobate crystals have been investigated. Experimental results show that each absorption band consists of three components. The absorption peaks were considered to relate to the stretching vibration of protons located at 336 pm O-O bonds in oxygen triangles nearest to the Li site. The absorption peak corresponds to protons directly substituting for ions; the 3481 and peaks are suggested to be associated with protons occupying intrinsic defects near and two different ion environments cause these two absorption peaks.