Calorimetric and dielectric studies of phase transitions in ammonium nitrite

Article abstract of DOI:10.1016/0021-9614(88)90219-4

The heat capacity of ammonium nitrite has been measured between 13 and 310 K with an adiabatic calorimeter.Two phase transitions were found at (181.3 +/- 0.2) K and (276.5 +/- 0.1) K.The molar enthalpy and molar entropy of the phase transition were determined as follows: (670 */- 30) J*mol^-1 and (3.70 +/- 0.17) J*K^-1*mol^-1 for the former, and (1240 +/- 60) J*mol^-1 and (4.84 +/- 0.23) J*K^-1*mol^-1 for the latter.Another phase transition was confirmed at 346 K for which the molar entropy of transition ca. 20 J*K^-1*mol^-1 was estimated from d.t.a.A strong peak in the dielectric permittivity occurred at 276 K second-order transition.The first-order transition at 181 K was dielectrically neutral.The intermediate phase stable between 181 and 276 K was supercooled to 13 K as a metastable phase for which a residual molar entropy (1.4 +/- 0.5) J*K^-1*mol^-1 was determined.