Synthesis and ferroelectric properties of rare earth compounds with tungsten bronze-type structure

Polycrystalline materials with a general formula Pb2Na0.8R0.2Nb4.8Fe0.2O15 (R = Dy, Eu, Sm, Nd, La) have been synthesized, in air by a high temperature solid state reaction method. X-ray diffraction study, at room temperature, revealed that they crystallize in the tungsten bronze-type structure. Dielectric properties were performed, in the temperature range 25–500 °C, at three different frequencies 10, 100 and 1000 kHz. The ferroelectric transition is pronounced by a large thermal hysteresis during the heating and cooling cycles. The determined Curie temperature values Tc were discussed as a function of rare earth size. Phase transitions around Tc for the investigated compounds were confirmed by differential scanning calorimetry (DSC) measurements.