signature=9f46406ae6d5b233c98d06c509970186,The phase diagram of ammonium nitrate

摘要：

The pressure-temperature (P-T) phase diagram of ammonium nitrate (AN) [NH4NO3] has been determined using synchrotron x-ray diffraction (XRD) and Raman spectroscopy measurements. Phase boundaries were established by characterizing phase transitions to the high temperature polymorphs during multipleP-Tmeasurements using both XRD and Raman spectroscopy measurements. At room temperature, the ambient pressure orthorhombic (Pmmn) AN-IV phase was stable up to 45 GPa and no phase transitions were observed. AN-IV phase was also observed to be stable in a largeP-Tphase space. The phase boundaries are steep with a small phase stability regime for high temperature phases. AP-V-Tequation of state based on a high temperature Birch-Murnaghan formalism was obtained by simultaneously fitting theP-Visotherms at 298, 325, 446, and 467 K, thermal expansion data at 1 bar, and volumes fromP-Tramping experiments. Anomalous thermal expansion behavior of AN was observed at high pressure with a modest negative thermal expansion in the 3–11 GPa range for temperatures up to 467 K. The role of vibrational anharmonicity in this anomalous thermal expansion behavior has been established using highP-TRaman spectroscopy.

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