Electro-optic and electrical properties in Hafnium-doped congruent   lithium-niobate crystals
  We report the optical and dielectric properties in hafnium (Hf)-doped lithium niobate (LN) crystals. We investigated samples of congruent composition with various doping concentration varying from 0 to 8 mol%. The clamped and unclamped values of the electro-optic coefficient r 22 of Hf-doped LN and the corresponding dielectric permittivity as well, have been experimentally determined and compared with the results obtained in undoped congruent LN crystals. We show that the electro-optic and dielectric properties are only slightly affected by the introduction of hafnium ions, and therefore Hf-doped LN has the advantage of low photorefractive damage compared with the undoped congruent LN. 
Mustapha Abarkan (LMOPS), Michel Aillerie (LMOPS), Jean-Paul   Salvestrini (LMOPS), Marc D. Fontana (LMOPS), Edvard Kokanyan