Structure of Intermediate Phase II of LiNH₂ under High Pressure

A new intermediate phase (phase II) was found between phases I and III in LiNH₂ in the pressure range of 10 to 13 GPa through the analysis of infrared and powder X-ray diffraction measurements to 25 GPa at room temperature. This result agreed with the prediction of a stable phase between phases I and III through theoretical calculations. Powder X-ray diffraction measurement and DFT calculation showed that this phase has a monoclinic structure with space group <i>C</i>2/<i>c</i> (<i>Z</i> = 8), which is the same structure as that of a slightly tilted crystal lattice of the <i>Fddd</i> structural model. The enthalpy of the <i>C</i>2/<i>c</i> structure was also found to be almost the same as that of the <i>Fddd</i> structure

Structure of Intermediate Phase II of LiNH₂ under High Pressure

A new intermediate phase (phase II) was found between phases I and III in LiNH₂ in the pressure range of 10 to 13 GPa through the analysis of infrared and powder X-ray diffraction measurements to 25 GPa at room temperature. This result agreed with the prediction of a stable phase between phases I and III through theoretical calculations. Powder X-ray diffraction measurement and DFT calculation showed that this phase has a monoclinic structure with space group <i>C</i>2/<i>c</i> (<i>Z</i> = 8), which is the same structure as that of a slightly tilted crystal lattice of the <i>Fddd</i> structural model. The enthalpy of the <i>C</i>2/<i>c</i> structure was also found to be almost the same as that of the <i>Fddd</i> structure

Structure of Intermediate Phase II of LiNH₂ under High Pressure

A new intermediate phase (phase II) was found between phases I and III in LiNH₂ in the pressure range of 10 to 13 GPa through the analysis of infrared and powder X-ray diffraction measurements to 25 GPa at room temperature. This result agreed with the prediction of a stable phase between phases I and III through theoretical calculations. Powder X-ray diffraction measurement and DFT calculation showed that this phase has a monoclinic structure with space group <i>C</i>2/<i>c</i> (<i>Z</i> = 8), which is the same structure as that of a slightly tilted crystal lattice of the <i>Fddd</i> structural model. The enthalpy of the <i>C</i>2/<i>c</i> structure was also found to be almost the same as that of the <i>Fddd</i> structure

Structural Analysis of Some High-Pressure Stable and Metastable Phases in Lithium Borohydride LiBH₄

Some high-pressure structures of lithium borohydride (LiBH₄) were analyzed using the Rietveld refinement for high-pressure X-ray diffraction data up to 50 GPa, and also by the density functional theory (DFT) calculation, the molecular dynamics (MD) simulation and Raman scattering spectrum. The structure of the first high-pressure phase at room temperature (phase III) was proposed to be an <i>I</i>4₁/<i>acd</i> structure, whose unit cell is composed of a √2 × √2 × 2 supercell of the previously reported <i>Ama</i>2 structure. However, the BH₄^– ions in our model were found to have different orientations from that of the <i>Ama</i>2 model. The structure of the second high-pressure phase (phase V′) that appeared at 17 GPa was proposed to be the tetragonal <i>I</i>4<i>/mmm</i> structure, where the hydrogen atoms were disordered in the same way as that of an ambient phase of NaBH₄ (<i>Fm</i>3̅<i>m</i> structure). When the pressure was elevated to 30 GPa, the tetragonal <i>I</i>4<i>/mmm</i> structure gradually deformed to a cubic <i>Fm</i>3̅<i>m</i> structure, which had previously been reported as the structure of the thermodynamically stable phase V. This suggests that phase V′ is a metastable phase that appeared during the transformation from phase III to phase V. These results were also observed in the high-pressure Raman spectra. Phase V tended to lose its structure gradually at 50 GPa, which might be an indication of another pressure-induced transformation

Distinct Responses to Mechanical Grinding and Hydrostatic Pressure in Luminescent Chromism of Tetrathiazolylthiophene

Luminescent mechanochromism has been intensively studied in the past few years. However, the difference in the anisotropic grinding and the isotropic compression is not clearly distinguished in many cases, in spite of the importance of this discrimination for the application of such mechanochromic materials. We now report the distinct luminescent responses of a new organic fluorophore, tetrathiazolylthiophene, to these stresses. The multichromism is achieved over the entire visible region using the single fluorophore. The different mechanisms of a blue shift by grinding crystals and of a red shift under hydrostatic pressure are fully investigated, which includes a high-pressure single-crystal X-ray diffraction analysis. The anisotropic and isotropic modes of mechanical loading suppress and enhance the excimer formation, respectively, in the 3D hydrogen-bond network