Synthesis, Crystal Structure, Local Structure, and Magnetic Properties of Polycrystalline and Single-Crystalline Ce2Pt6Al15

Asymmetry, such as non-centrosymmetry in the crystal or chiral structure and local symme-try breaking, plays an important role in the discovery of new phenomena. The honeycomb structure is an example of an asymmetric structure. Ce2Pt6Al15 is a candidate for a frustrated system with honeycomb Ce-layers, which have been reported to show near the quantum critical point. However, the ground state of Ce2Pt6Al15 depends on the sample, and analysis of the crystal structure is difficult due to the presence of stacking disorder. We synthesized polycrystalline Ce2Pt6Al15 using arc melting method (AM-Ce2Pt6Al15) and single-crystalline Ce2Pt6Al15 using flux method (F-Ce2Pt6Al15). The prepared samples were characterized by electron probe micro-analysis (EPMA), single and powder X-ray diffraction methods, measured magnetic properties and X-ray absorption spectroscopy (XAS). The composition ratio of AM-Ce2Pt6Al15 was stoichiometric, although it contained a small amount (i.e., a few percent) of the impurity Ce2Pt9Al16. Meanwhile, the composition ratio of F-Ce2Pt6Al15 deviated from stoichiometry. The X-ray absorption fine structure (XAFS) spectrum of AM-Ce2Pt6Al15 at the Ce L3-edge was similar to that of CeF3, which possesses the Ce3+ configuration, indicating that the valence of Ce in Ce2Pt6Al15 is trivalent; this result is consistent with that for the magnetic susceptibility. To determine the precise structure, we analyzed the extended X-ray absorption fine structure (EXAFS) spectra of Ce L3- and Pt L3-edges for Ce2Pt6Al15, and found that the EXAFS spectra of Ce2Pt6Al15 can be explained not as a hexagonal Sc0.6Fe2Si4.9-type structure but, instead, as an orthorhombic structure with honeycomb structure.