Dielectric Studies on the Ferroelectric Phase Transition in AgNg(NO₂)₂

Abstract

Single crystals of ferroelectric AgNa(NO₂)₂ were grown from aqueous solution containing proper amounts of NaNO₂ and AgNO₂, and dielectric properties were measured. The dielectric constant along the b-direction ε_b at 1 kHz shows a sharp maximum at the Curie point of 38°C. Above the Curie point, ε_b obeys the Curie-Weiss law with the Curie constant of 4.7×10³°K. The ferroelectric-to-paraelectric phase transition is of the first kind. A conspicuous dielectric dispersion is observed in the frequency region of 1 kHz∼1 MHz. Ferroelectric hysteresis loops are observed in a narrow temperature range of about 2°C below the Curie point. Difference between the tansition behaviors of AgNa(NO₂)₂ and NaNO₂ is discussed. A picture of the composition dependence of the transition points in NaNO₂–AgNO₂ system is given from differential thermal analysis measurements.