M. J. Mehl, D. Hicks, C. Toher, O. Levy, R. M. Hanson, G. L. W. Hart, and S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 1, Comp. Mat. Sci. 136, S1-S828 (2017). (doi=10.1016/j.commatsci.2017.01.017)
D. Hicks, M. J. Mehl, E. Gossett, C. Toher, O. Levy, R. M. Hanson, G. L. W. Hart, and S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 2, Comp. Mat. Sci. 161, S1-S1011 (2019). (doi=10.1016/j.commatsci.2018.10.043)
D. Hicks, M.J. Mehl, M. Esters, C. Oses, O. Levy, G.L.W. Hart, C. Toher, and S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 3, Comp. Mat. Sci. 199, 110450 (2021). (doi=10.1016/j.commatsci.2021.110450)
Ammonium Nitrate exists in a variety of forms, (Hermann, 1937) depending on the temperature: \[\begin{array}{ccccc} \text{ Phase } & \text{ Temperature ${^\circ}$C } & \text{ Strukturbericht } & \text{ Page } \\ \text{ I } &\text{ 125 $--$ 170 } &\text{ $G0_{8}$ } &\href{./AB_cP2_221_a_b.NH4.NO3.html}{\text{AB_cP2_221_a_b.NH4.NO3}} &\text{ (this structure) } \\ \text{ II } &\text{ 84 $--$ 125 } &\text{ $G0_{9}$ } &\href{./ABC3_tP10_100_b_a_bc.html}{\text{ABC3_tP10_100_b_a_bc}} &\text{ } \\ \text{ III } &\text{ 32 $--$ 84 } &\text{ $G0_{10}$ } &\href{./ABC3_oP20_62_c_c_cd.N.NH4.O.html}{\text{ABC3_oP20_62_c_c_cd.N.NH4.O}} &\text{ } \\ \text{ IV } &\text{ -17 $--$ 32 } &\text{ $G0_{11}$ } &\href{./A4B2C3_oP18_59_ef_ab_af.html}{\text{A4B2C3_oP18_59_ef_ab_af}} &\text{ } \\ \text{ V } &\text{ $< -17$ } &\text{ Gwihabaite } &\href{./A4B2C3_tP72_77_8d_ab2c2d_6d.html}{\text{A4B2C3_tP72_77_8d_ab2c2d_6d2}} &\text{ }\end{array}\]
In the $G0_{8}$ structure, both the NH4+ and NO3– ions rotate freely about their centers of mass (Kracek, 1931). The two ions sit on the same sites as atoms in the CsCl ($B2$) structure.
F. C. Kracek, S. B. Hendricks, and E. Posnjak, Group Rotation in Solid Ammonium and Calcium Nitrates, Nature 128, 410–411 (1931), doi:10.1038/128410b0.
Found in
C. Hermann, O. Lohrmann, and H. Philipp, eds., Strukturbericht Band II 1928–1932 (Akademische Verlagsgesellschaft M. B. H., Leipzig, 1937).