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  1. Abstract High pressure is an effective tool to induce exotic quantum phenomena in magnetic topological insulators by controlling the interplay of magnetic order and topological state. This work presents a comprehensive high-pressure study of the crystal structure and magnetic ground state up to 62 GPa in an intrinsic topological magnet EuSn 2 P 2 . With a combination of high resolution X-ray diffraction, 151 Eu synchrotron Mössbauer spectroscopy, X-ray absorption spectroscopy, molecular orbital calculations, and electronic band structure calculations, it has been revealed that pressure drives EuSn 2 P 2 from a rhombohedral crystal to an amorphous phase at 36 GPa accompanied by a fourfold enhancement of magnetic ordering temperature. In the pressure-induced amorphous phase, Eu ions take an intermediate valence state. The drastic enhancement of magnetic ordering temperature from 30 K at ambient pressure to 130 K at 41.2 GPa resulting from Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions likely attributes to the stronger Eu–Sn interaction at high pressure. These rich results demonstrate that EuSn 2 P 2 is an ideal platform to study the correlation of the enhanced RKKY interactions, disordered lattice, intermediate valence, and topological state.
    Free, publicly-accessible full text available December 1, 2023
  2. Nanocrystalline olivine-structured Mg2SiO4 and MgCoSiO4, with an average particle size of 27 nm and 31 nm, respectively, were successfully synthesized from oxide precursors via mechanochemical methods. The two nanocrystalline products were obtained after milling for 360 min and displayed high concentrations of Mg2SiO4 (>94%) and MgCoSiO4 (>95%), together with minor amounts of WC (~3%) contaminant originating as debris abraded off milling balls and chambers. The macroscopic temperature monitoring of the grinding jars during milling trials recorded a peak temperature of 75 °C. A combination of analytical techniques that included XRD, TEM, SAED, and EDS were employed for the characterization of the synthesized products.
    Free, publicly-accessible full text available March 1, 2023
  3. Abstract Olivine is the most abundant mineral in the Earth's upper mantle and subducting slabs. Studying the structural evolution and equation of state of olivine at high-pressure is of fundamental importance in constraining the composition and structure of these regions. Hydrogen can be incorporated into olivine and significantly influence its physical and chemical properties. Previous infrared and Raman spectroscopic studies indicated that local structural changes occur in Mg-rich hydrous olivine (Fo ≥ 95; 4883–9000 ppmw water) at high-pressure. Since water contents of natural olivine are commonly <1000 ppmw, it is inevitable to investigate the effects of such water contents on the equation of state (EoS) and structure of olivine at high-pressure. Here we synthesized a low water content hydrous olivine (Fo95; 1538 ppmw water) at low SiO2 activity and identified that the incorporated hydrogens are predominantly associated with the Si sites. We performed high-pressure single-crystal X-ray diffraction experiments on this olivine to 29.9 GPa. A third-order Birch-Murnaghan equation of state (BM3 EoS) was fit to the pressure-volume data, yielding the following EoS parameters: VT0 = 290.182(1) Å3, KT0 = 130.8(9) GPa, and K′T0 = 4.16(8). The KT0 is consistent with those of anhydrous Mg-rich olivine, which indicates that such lowmore »water content has negligible effects on the bulk modulus of olivine. Furthermore, we carried out the structural refinement of this hydrous olivine as a function of pressure to 29.9 GPa. The results indicate that, similar to the anhydrous olivine, the compression of the M1-O and M2-O bonds are comparable, which are larger than that of the Si-O bonds. The compression of M1-O and M2-O bonds of this hydrous olivine are comparable with those of anhydrous olivine, while the Si-O1 and Si-O2 bonds in the hydrous olivine are more compressible than those in the anhydrous olivine. Therefore, this study suggests that low water content has negligible effects on the EoS of olivine, though the incorporation of water softens the Si-O1 and Si-O2 bond.« less