Linear electro-optic coefficients r13 and r33 of LiNbO3 crystal were measured in the setup of Mach-Zehnder interferometer with He-Ne laser. Sample was placed in closed circuit He cryostat, so temperature dependency was investigated from 150K to 330K. Electro-optical coefficients r33 and r13 were constant in this temperature range. In the measured frequency range 200 Hz-10 kHz, there is no change of the E-O coefficients with frequency.
"Temperature dependence of electro-optic coefficients of LiNbO3 crystals", Proc. SPIE 5036, Photonics, Devices, and Systems II, (8 July 2003); doi: 10.1117/12.498513; https://doi.org/10.1117/12.498513