Electronic Phase Separation in Iron Selenide(Li,Fe)OHFeSe Superconductor System

The phenomenon of phase separation into antiferromagnetic（AFM） and superconducting（SC） or normal-state regions has great implication for the origin of high-temperature（high-T_c） superconductivity. However, the occurrence of an intrinsic antiferromagnetism above the T_c of（Li,Fe）OHFe Se superconductor is questioned. Here we report a systematic study on a series of（Li,Fe）OHFe Se single crystal samples with T_c up to ～41 K. We observe an evident drop in the static magnetization at T_（afm） ～ 125 K, in some of the SC（T_c 38 K, cell parameter c■9.27 ？） and non-SC samples. We verify that this AFM signal is intrinsic to（Li,Fe）OHFe Se. Thus, our observations indicate mesoscopic-to-macroscopic coexistence of an AFM state with the normal（below T_（afm）） or SC（below T_c） state in（Li,Fe）OHFe Se. We explain such coexistence by electronic phase separation, similar to that in high-T_c cuprates and iron arsenides. However, such an AFM signal can be absent in some other samples of（Li,Fe）OHFe Se, particularly it is never observed in the SC samples of T_c 38 K, owing to a spatial scale of the phase separation too small for the macroscopic magnetic probe. For this case, we propose a microscopic electronic phase separation. The occurrence of two-dimensional AFM spin fluctuations below nearly the same temperature as T_（afm）, reported previously for a（Li,Fe）OHFe Se（T_c ～ 42 K） single crystal, suggests that the microscopic static phase separation reaches vanishing point in high T_c（Li,Fe）OHFe Se. A complete phase diagram is thus established. Our study provides key information of the underlying physics for high-T_c superconductivity.

Superconductivity in an intermetallic oxide Hf_(3)Pt_(4)Ge_(2)O

Discovery of a new superconductor with distinct crystal structure and chemistry often provides great opportunity for further expanding superconductor material base,and also leads to better understanding of superconductivity mechanisms.Here,we report the discovery of superconductivity in a new intermetallic oxide Hf_(3)Pt_Ge_(2)O synthesized through a solid-state reaction.The Hf_(3)Pt_Ge_(2)O crystallizes in a cubic structure(space group Fm-3 m)with a lattice constant of a=1.241 nm,whose stoichiometry and atomic structure are determined by electron microscopy and x-ray diffraction techniques.The superconductivity at 4.1 K and type-II superconducting nature are evidenced by the electrical resistivity,magnetic susceptibility,and specific heat measurements.The intermetallic oxide Hf_(3)Pt_Ge_(2)O system demonstrates an intriguing structural feature that foreign oxygen atoms can be accommodated in the interstitial sites of the ternary intermetallic framework.We also successfully synthesized a series of Hf_(3)Pt_Ge_(2)O1+δ(-0.25≤δ≤0.5),and found theδ-dependent superconducting transition temperature Tc.The atomic structure and the electronic structure are also substantiated by first-principles calculations.Our results present an entirely new family of superconductors with distinct structural and chemical characteristics,and could attract research interest in further finding new superconductors and exploring novel physics pertaining to the 5 d-electron in these intermetallic compound systems.

Geometric edge effect on the interface of Au/CeO_(2)nanocatalysts for CO oxidation

The oxide supports play a crucial role in anchoring and promoting the active metal species by geometric confinement and chemical interaction.The design and synthesis of the well-defined oxide support with specific morphology such as size,shape,and exposed facets have attracted extensive research efforts,which directly reflects on their catalytic performance.In this study,using an Au/CeO_(2)-nanorod model catalyst,we demonstrate an edge effect on the Au/CeO_(2)interfacial structure,which shows a prominent effect on the structure-performance relationship in the CO oxidation reaction.This specific“edge-interface”structure features an“edge-on”Au nanoparticles position on rod-shaped CeO_(2)support,confirmed by atomic-scale electron microscopy characterization,which introduces additional degrees of freedom in coordination environment,chemical state,bond length,and strength.Combined with theocratical calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)investigations,we confirmed that this“edge-interface”has distinct adsorption properties due to the change of O vacancy formation energy as well as the chemical states of Au resulting from the electron transfer and redistribution between the metal and the support.These results demonstrate a non-conventional geometric effect of rod-shaped supported metal catalysts on the catalytic performance,which could provide insights into the atomic-precise utilization of catalysts.