Spontaneous birefrigence of gadolinium molybdate

Electro- and piezooptical hysteresis loops and the dispersion of birefringence of Gd2(MoO4)3 pure and activated by Nd3+(0,5%) ions crystals were measured at room temperature in static fields. The coercive field decrease of poly- and monodomain crystalline samples is found in the course of multiple repolarization from hopping variation of interference conoscopic pictures, observable in rays of a helium-neon laser. The coercive field remains unchangable only after five cycles. For pure and activated crystals the coercive field is about 3,4 kV.cm-1. Experimental measurement of the value, that is characteristic of birefringence variation, was conducted using mica quarter-wavelength plates lambda/4 for various wavelengths at polarimetric devices, mounted on the basis of a helium-neon laser and a monochromator. The accuracy of the birefringence measurement was +-1 x 10-1. The electro- and piezooptical hysteresis loops obtained had an anomalous behaviour that is indicative for extrinsic ferroelectrics. In addition to the absorption band, corresponding to lambda = 312 nm, absorption bands at 360 and 65O nm in activated crystals were also observed. The presence of the latter bands was revealed in the birefringence dispersion. It is supposed that various behaviour of the birefringence dispersion at the wavelengths is related to polarization peculiarities