Percolation-induced resistivity drop in lutetium dihydride with controllable electrical conductivity over six orders of magnitude

The recent report of near-ambient superconductivity in the nitrogen-doped lutetium hydride has attracted considerable attention.Subsequent follow-up studies confirmed the pressure-induced color changes in both N-free and N-doped LuH_(2) but failed to reproduce superconductivity. It remains a puzzle why the samples in the original report exhibited pronounced resistance anomaly reminiscent of the superconducting transition. Here, we show that percolation of metallic grains with high conductivity through the insulating surfaces in cold-pressed LuH_(2) samples can occasionally produce sharp resistance drops, which even display magnetic field and/or current dependences but stay far from zero resistance. The insulating surface of LuH2grain should be attributed to the modification of hydrogen stoichiometry or the contamination by oxygen/nitrogen, resulting in an increase of resistance by over six orders of magnitude. Such an effect is more significant than that discovered recently in LaH_(3±x), which may indicate that LuH_(2) can be a potential superionic conductor. Our results call for caution in asserting the resistivity drops as superconductivity and invalidate the background subtraction in analyzing the corresponding resistance data.

Molten-salt synthesis of porous La0.6Sr0.4Co0.2Fe0.8O2.9 perovskite as an efficient electrocatalyst for oxygen evolution

The development of an efficient and low-cost electrocatalyst for the oxygen evolution reaction （OER） via an eco-efficient route is a desirable, although challenging, outcome for overall water splitting. Herein, an iron-rich La0.6Sr0.4Co0.2Fe0.8O2.9 （LSCF28） perovskite with an open porous topographic structure was developed as an electrocatalyst by a straightforward molten-salt synthesis approach. It was found that porosity correlates with both the iron content and the molten-salt approach. Benefiting from the large surface area, high activity of the porous internal surface, and the optimal electronic configuration of redox sites, this inexpensive material exhibits high performance with a large mass activity of 40.8A·g^-1 at a low overpotential of 0.345 V in 0.1 M KOH, surpassing the state-of-the-art precious metal IrO2 catalyst and other well-known perovskites, such as Ba0.5Sr0.5Co0.8Fe0.2O3 and SRCoO2.7. Our work illustrates that the molten- salt method is an effective route to generate porous structures in perovskite oxides, which is important for energy conversion and storage devices.

Large magnetic entropy change in weberite-type oxides Gd_(3)MO_(7)(M=Nb,Sb,and Ta)

In the present work,the structure,magnetic properties,and cryogenic magnetocaloric effect of weberite-type oxides Gd_(3)MO_(7)(M=Nb,Sb,and Ta)are reported through powder X-ray diffraction,bulk susceptibility,and heat capacity measurements,as well as scaling law analysis and a mean-field approach.A remarkably large isothermal magnetic entropy change of 354.0 m J K^(-1)cm^(-3)is observed for Gd_(3)SbO_(7)under an external field of 9 T at 2.0 K.The relative cooling power is estimated to be 618.9 J kg^(-1)(4.8 J cm^(-3))for an applied field of 8.9 T,with the largest adiabatic temperature change being 22.4 K at 6.3 K.The magnetocaloric performance of these oxides is quite impressive when compared with the benchmark magnetic refrigerant,gadolinium gallium garnet(Gd_(3)Ga_(5)O_(12),GGG).Therefore,Gd_(3)MO_(7)(M=Nb,Sb,and Ta)are promising alternatives for cryogenic cooling techniques,especially for the magnetic liquefaction of helium.

Superconductivity of a cuprate with compressed local octahedron

Since the historical discovery of high Tc superconductivity(HTS)of La2CuO4 in 1986[1],the superconductivity me chanism of copper oxides remains one of the biggest mysteries in the field of condensed matter physics[2-10].High-Tc cuprates crystallize into layered perovskite structure,as well as copper oxygen octahedron coordination.In octahedron symmetry,the 3d orbitals of Cu^2+with a 3d^9 configuration degenerate into two top eg and three lower t2g orbitals.

Orbital selection of the double [CuO2] layer compound Ca3Cu2O4Cl2

The discovery of high-temperature copper oxide superconductors(HTS)by Bednorz and Muller[1]in 1986 opened up a new field of superconductivity.Since then,several different families of materials have been discovered with greatly increased superconducting critical temperature(Tc)[2].Oxychloride cuprates,Can+1CunO2wCl2,are one such type of parent compound of high Tc cuprate superconductors.There are two members in this family known so far that can exist at ambient pressure:Ca2CuO2Cl2(single[Cu02]layer CCOC)and Ca3Cu2O4Cl2(double[CuO2]layer CCOC).Both are composed of a[CuO2]plane with the apical oxygen replaced by chlorine atoms.