276. The crystal structure of ammonium nitrate III, and atomic scattering factors in ionic crystals

Infrared Spectra and Crystalline Phase Transitions of Ammonium Nitrate

“…According to Goodivin and IYhetstone phase 111 has space group Vh16 (Pbnm) with four molecules per unit cel l (6).…”

The structure of phase III ammonium nitrate

“…The ammonium ions are also considered to have their N atoms on mirror planes. The Goodwin & Whetstone (1947) model does not provide the ammonium ion orientations, but these ions were found to be disordered (about their N atom positions) between two different orientations and their structural arrangements were determined in the present work. The H atoms of the ion are located essentially tetrahedrally about their N atom, a 4 axis of the ion being parallel to a.…”

“…The model proposed by Goodwin & Whetstone (1947) was used as the starting model. This consists of an orthorhombic structure based on the space group Pnma.…”

“…Five distinct phases with reversible transitions between them in the sequence V-IV-III-II-I have been reported (Nagatani, Seiyama, Sakiyama, Suga & Seki, 1967). At room temperature, phase IV has an orthorhombic crystal structure (Choi, Mapes & Prince, 1972), which transforms to a tetragonal phase V structure (Amor6s, Arrese & Canut, 1962) when cooled below 255 K. On heating above room temperature, transitions occur to an orthorhombic phase III structure at 305.3 K (Goodwin & Whetstone, 1947), a tetragonal phase II structure at 357 K and to a cubic phase I structure above 328 K (Ahtee, Kurki-Suonio, . The corresponding transitions have been found also for deuterated ammonium nitrate, the transition temperatures being only slightly affected by deuteration (Juopperi, 1972).…”

The crystal structure of phase II ammonium nitrate

“…Five distinct phases with reversible transitions between them in the sequence V-IV-III-II-I have been reported (Nagatani, Seiyama, Sakiyama, Suga & Seki, 1967). At room temperature, phase IV has an orthorhombic crystal structure (Choi, Mapes & Prince, 1972), which transforms to a tetragonal phase V structure (Amor6s, Arrese & Canut, 1962) when cooled below 255 K. On heating above room temperature, transitions occur to an orthorhombic phase III structure at 305.3 K (Goodwin & Whetstone, 1947), a tetragonal phase II structure at 357 K (Shinnaka, 1956) and to a cubic phase I structure above 398 K (Shinnaka, 1959a). Dry crystals (without occluded water) have been found to transform directly from the phase IV structure to phase II on heating at 328 K (Brown & McLaren, 1962).…”