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Fe5–xGeTe2is a two-dimensional van der Waals material that exhibits ferromagnetic order with a high Curie temperature (TC) of around room temperature. In addition to TC, two magnetic transitions occur with decreasing temperature, and a charge-ordered state is observed at low temperatures. We employed Ge Kα X-ray fluorescence holography (XFH) for Fe5–xGeTe2to directly investigate the local structure in the charge-ordered state, i.e., the 3×3superstructure. The Ge Kα XFH results revealed local atomic structures around the Ge atom, thus clarifying the simultaneous locations and arrangements of the Te, Fe, and Ge atoms. The atomic positions relative to the Ge atom are useful for understanding the coexistence of the ideal 1 × 1 structure and 3×3superstructure found in the charge-ordered state.

A graphite-like material boron carbide (BCx) was synthesized under various heat treatment conditions and extensively characterized. First, we synthesized the BCxprecursor phase by a single-step reaction using a mixed solution of BBr3and C6H6. We confirmed that the precursor phase had a graphite-like structure with B–C chemical bonds, but its crystallinity was poor. To improve their crystallinity, we annealed the precursor sample at high temperature using a high-frequency furnace and determined the annealing condition. We also investigated the magnetic properties of BCx. The high-temperature annealing for the precursor phase yields the highest Pauli paramagnetic susceptibility χPauli, indicating the highest density of states at the Fermi level. Accordingly, the high-temperature treatment for the precursor phase is significant to improve its crystallinity and physical properties. In addition, we synthesized a Ti-intercalated material TiBC by using the same procedure as that for making the BCxprecursor phase. The crystal structure can be indexed by the AlB2structure, indicating that Ti atoms are intercalated between the BC layers. The χPaulivalue of TiBC is obtained to be 1 order of magnitude smaller than that of BCx, suggesting the compensation of hole carriers by electron doping through Ti intercalation into the BCxsystem.

The structural and superconducting properties of the Bi-based superconductor Bi2Rh3(Se1–xSx)2were investigated over a wide pressure range. Bi2Rh3Se2is a superconductor with a superconducting transition temperature, Tc, of less than ∼1.0 K, whereas Bi2Rh3S2is a nonsuperconductor. The former shows a clear charge density wave (CDW) phase transition at 240 K and the latter shows a first-order structural phase transition at 165 K, providing the supercell structure. Both compounds have the same crystal structure at ambient temperature and pressure (monoclinic, space group of C2/m(No. 12)). This implies the possible formation of solid solution-like phases Bi2Rh3(Se1–xSx)2. In this study, we prepared Bi2Rh3(Se1–xSx)2(x= 0–1.0) and investigated its superconducting properties and phase transitions at different xvalues. Because the superconducting properties and temperature causing the phase transition (Tpt) are quite different between Bi2Rh3Se2and Bi2Rh3S2, their variation against xis quite intriguing from the viewpoint of the pursuit of physical properties via the replacement of Se with S. In this study, the features of the superconductivity and crystal structure against xwere fully explored to depict the phase diagram. Moreover, we investigated the pressure (p) dependence of superconductivity and phase transition (CDW or the first-order structural transition) to clarify the interplay between the two ordered states.