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The structural stability and electrical properties of AlB2-type MnB2 were studied based on high pressure angle-dispersive x-ray diffraction, in situ electrical resistivity measured in a diamond anvil cell (DAC) and first-principles calculations under high pressure. The x-ray diffraction results show that the structure of AlB2-type MnB2 remains stable up to 42.6 GPa. From the equation of state of MnB2, we obtained a bulk modulus value of 169.9±3.7 GPa with a fixed pressure derivative of 4, which indicates that AlB2-type MnB2 is a hard and incompressible material. The electrical resistance undergoes a transition at about 19.3 GPa, which can be explained by a transition of manganese 3d electrons from localization to delocalization under high pressure. [ABSTRACT FROM AUTHOR]

A system for the investigation of the magnetic properties of materials under high pressure is fabricated based on diamond anvil cell (DAC) technology. The system is designed with an improved coil arranged around the diamond of a non-magnetic DAC. Using this system, the magnetic transition of ferromagnetic (Fe) sample under increasing pressure can be observed. We successfully obtain the evolution of magnetic properties as a function of applied pressure reaching 26.9 GPa in the Fe sample. A magnetic transition is observed at approximately 13 GPa, which is consistent with the theoretical prediction. [ABSTRACT FROM AUTHOR]

Multiple phase transitions are detected in sodium amide (NaNH2), an important hydrogen storage material, upon compression in diamond anvil cells (DAC) by using Raman spectroscopy and x-ray diffraction (XRD) measurements. Additional Bragg reflections appear on lower and higher angle sides of the original ones at ∼ 1.07 GPa and 1.84 GPa, accompanied by obvious changes in Raman spectroscopy, respectively. It reveals that NaNH2 undergoes the high-pressure phase sequence (α–β–γ) up to 20 GPa at room temperature. Spectral analysis indicates an orthorhombic structure with PBAN space group for the γ phase. We also experimentally observe high pressure induced recrystallization in alkaline amide compounds for the first time. [ABSTRACT FROM AUTHOR]

The high-pressure behavior of solid hydrogen has been investigated by in situ Raman spectroscopy upon compression to 300 GPa at ambient temperature. The hydrogen vibron frequency begins to decrease after it initially increases with pressure up to 38 GPa. This softening behavior suggests the weakening of the intramolecular bond and the increased intermolecular interactions. Above 237 GPa, the vibron frequency softens very rapidly with pressure at a much higher rate than that of phase III, corresponding to transformation from phase III into phase IV. The phase transition sequence has been confirmed from phase I to phase III and then to phase IV at 208 and 237 GPa, respectively. Previous theoretical calculations lead to the proposal of an energetically favorable monoclinic C2/c structure for phase III and orthorhombic Pbcn structure for phase IV. Up to 304 GPa, solid hydrogen is not yet an alkali metal since the sample is still transparent. [ABSTRACT FROM AUTHOR]

A magnetic-parameter measurement system for study of ferromagnetic materials under high pressure using a diamond-anvil cell is built. The factors affecting the measurement sensitivity are analyzed and the possibility of improving the sensitivity is mentioned. Based on the system, the magnetization curves of iron as a function of pressure are obtained. The start point and end point of pressure-induced magnetic transition of iron are observed at room temperature. [ABSTRACT FROM AUTHOR]