Ferroelastic and ferroelectric behavior of the oxyfluoride Na3MoO3F3

Two phase transitions have been detected for Na 3 MoO 3 F 3 at 130 and 530°C by X-ray diffraction, μ -D.T.A. and dielectric measurements. The high temperature one is of ferroelastic, ferroelectric-prototype, paraelectric type. The structure of the monoclinic room temperature phase derives from that of Na 3 AlF 6 . The oxyfluoromolybdate of sodium is thus the first member of a new ferroelastic-ferroelectric family.