Large Volume Collapse during Pressure-Induced Phase Transition in Lithium Amide

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Abstract

The structural studies of lithium amide (LiNH2) have been performed by synchrotron X-ray diffraction measurements and ab initio density functional theoretical calculations up to 28.0 GPa. It is revealed that LiNH2 undergoes a reversible pressure-induced phase transitions from tetragonal phase (I-4) into the monoclinic phase (P21), which starts from about 10.3 GPa and completes at about 15.0 GPa. This transition is accompanied by about 11% large volume collapse, and this volume collapse is much larger than other complex ternary hydrides. The experimental pressure–volume data for the two phases of LiNH2 are fitted by third-order Birch–Murnaghan equation of state, yielding B0 of 37.2 (1.7) GPa for the tetragonal phase and 7.6 (4.9) GPa for the monoclinic phase with the pressure derivatives at 3.5. We also have calculated the total and partial density of states of the two phases in order to explore the mechanism of the volume reduction.

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