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

New-Structure-Type Fe-Based Superconductors: Ca<i>A</i>Fe₄As₄ (<i>A</i> = K, Rb, Cs) and Sr<i>A</i>Fe₄As₄ (<i>A</i> = Rb, Cs)

Fe-based superconductors have attracted research interest because of their rich structural variety, which is due to their layered crystal structures. Here we report the new-structure-type Fe-based superconductors Ca<i>A</i>Fe₄As₄ (<i>A</i> = K, Rb, Cs) and Sr<i>A</i>Fe₄As₄ (<i>A</i> = Rb, Cs), which can be regarded as hybrid phases between <i>Ae</i>Fe₂As₂ (<i>Ae</i> = Ca, Sr) and <i>A</i>Fe₂As₂. Unlike solid solutions such as (Ba_1–<i>x</i>K_<i>x</i>)­Fe₂As₂ and (Sr_1–<i>x</i>Na_<i>x</i>)­Fe₂As₂, <i>Ae</i> and <i>A</i> do not occupy crystallographically equivalent sites because of the large differences between their ionic radii. Rather, the <i>Ae</i> and <i>A</i> layers are inserted alternately between the Fe₂As₂ layers in the <i>c</i>-axis direction in <i>AeA</i>Fe₄As₄ (<i>AeA</i>1144). The ordering of the <i>Ae</i> and <i>A</i> layers causes a change in the space group from <i>I</i>4/<i>mmm</i> to <i>P</i>4/<i>mmm</i>, which is clearly apparent in powder X-ray diffraction patterns. <i>AeA</i>1144 is the first known structure of this type among not only Fe-based superconductors but also other materials. <i>AeA</i>1144 is formed as a line compound, and therefore, each <i>AeA</i>1144 has its own superconducting transition temperature of approximately 31–36 K

Crystal Structure and Superconductivity of BaIr₂Ge₇ and Ba₃Ir₄Ge₁₆ with Two-Dimensional Ba-Ge Networks

The Ba-Ir-Ge ternary compounds BaIr₂Ge₇ and Ba₃Ir₄Ge₁₆ exhibit superconductivity (SC) at 2.5 and 5.2 K, respectively. Detailed single-crystal structural analysis revealed that these compounds share unique quasi-two-dimensional networks composed of crown-shaped Ge rings that accommodate Ba atoms at the center, referred to as “edge-shared crown-shaped BaGe₁₆ polyhedra”. The layered Ba-Ge network yielded a modest anisotropy of 1.3–1.4 in the upper critical field, which is in good agreement with the band structure calculations. The Ba-Ge structural unit is similar to cage structures seen in various clathrates in which the anharmonic vibration of the central atoms, the so-called “rattling” behavior, brings about strong-coupling SC. However, each Ba-Ge unit is relatively small compared to these materials, which likely excludes the possibility of unconventional SC