Absorption bands (3525 to 3470/cm) were observed in doped crystals (except in the case of Cu or V doping). These bands were attributed to O-H vibrations. The H concentration in the doped crystals could be controlled by doping or by heat treatment. The activation energy for H-ion migration in the doped crystals was estimated to be between 0.6 and 0.7eV.

X.Tong, M.Zhang, A.Yariv, A.Agranat, R.Hofmeister, V.Leyva: Applied Physics Letters, 1996, 69[4], 479-81