Electrical and thermal studies of NaNO2

The present paper reports on experimental results on polycrystalline NaNO2 employing the dc resistivity, DTA, and unit cell parameters (measured by X-ray diffractometry) in the temperature range from 298 to 480 K. All the presented results confirm, in addition to the well-known phase transitions at 436.5 and 438 K, the existence of a second-order phase transition occurring at 448 K. We found clear evidences that the ferroelectric phase transition of NaNO2 is of second order close to the first-order one, and the rotation of the NO2- radical mostly takes place around the c-axis. The high-temperature phase transformation occurring at 448 K is thought to be due to the completely disordered arrangement of the NO2- radicals in the normal paraelectric phase.