Abstract
Birefringence Δnc of the improper ferroelectric Gd2(MoO4)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 Δnc was found to show unique behaviour in the vicinity of Tc. It is of importance that the linear electrooptic coefficient r63 changes its sign and manifests a sharp peak in the close vicinity of Tc. This result coincides qualitatively with the result reported by Kobayashi and Miyazaki, but disagrees with other reports.