Some peculiarities in dielectric and electrooptical properties of cadmium pyroniobate

Temperature dependences epsilon and.tgdelta of Cd2Nb2O7 monocrystals in the absence and at application of constant shifting fields as well as temperature dependences of square electrooptical coefficients are studied. It is shown that at temperatures above permittivity maximum (approximately 85 deg C) at least three phase transitions (-72 deg C, -68 deg C, -55 deg C) are observed, the transition at -55 deg C being observed only in strong electric fields. Improper ferroelectric phase existing in the temperature range -72 - -85 deg C is stable only in weak electric fields. The observed anomalies of electrooptical coefficients at temperatures -68 and -55 deg C confirm the existence of phase transitions