W.Kaminsky, S.Haussühl: Faraday effect and birefringence in othorhombic Li2Ge7O15 near the ferroelectric phase transition. Ferroelectrics letters 11 (1990) 63-67.
The tensor of the Faraday effect and its temperature derivatives were determined from the temperature dependence of Faraday rotation and inices of refraction of orthorhombic Li2Ge7O15 between 120K and 340K, wave length 633nm. A strong anomaly of the Verdet constant V33 and of the index n3 was observed passing through the transition at 284K. The ratio of the slopes of the Verdet constant V33 above and below the transition is about -2. This value corresponds to a second-order ferroelectric phase transition.