Raman Scattering and Phase Transition of Ammonium Nitrates

Polarized Raman spectra of single crystals are observed for the room-temperature phase NH4NO3(IV). The spectra in the low-frequency lattice vibration region as well as in the internal vibration region are well interpreted based on D2h13 structure. Raman spectra of powdered samples are measured at various temperatures covering whole phases NH4NO3 I–V. A characteristic feature of Raman spectrum is clarified for each phase. An abrupt spectral change occurs in the phase transition, indicating a first order transition. The splitting of Ag and B1g components of ν3 (asymmetric stretching mode of NO3− ion) in NH4NO3 is quite large, due to the strong interionic interaction between NH4+ and NO3− ions.