Optical properties of Gd2(MoO4)3 studied by high accuracy universal polarimeter (HAUP) method

Birefringence Δn c of the improper ferroelectric Gd 2 (MoO 4 ) 3 was accurately measured by using the HAUP (high accuracy universal polarimeter) method as a function of temperature and electric field. Electric field dependence of Δn c was found to show unique behaviour in the vicinity of T c . It is of importance that the linear electrooptic coefficient r 63 changes its sign and manifests a sharp peak in the close vicinity of T c . This result coincides qualitatively with the result reported by Kobayashi and Miyazaki, but disagrees with other reports