Fei Wu

Phase relations in the NdCoSi system at 800°C

Abstract Phase equilibria in the ternary Nd Cs Si system up to a Co:Nd atomic ratio of 2:1 and an Si:Nd atomic ratio of 3:5 were studied by means of X-ray powder diffraction. A total of seven ternary compounds were identified. Among the seven ternary compounds found in this system, the solid solubility of two compounds had not been reported previously: NdCo 13 , Si 4 with 2.5 ⩽ x ⩽ 4 and NdCo 11 , Si 4 with 1.2 ⩽ x ⩽ 1.8. Other new information includes the crystal structure of NdCo 13 , Si 4 . It has a tetragonal structure, related to the NaZn 13 -type, with a = 7.811−7.763A, c = 11.430−11.464A, and the atomic ordering is similar to Ce 2 Ni 17 Si 4 . A limited solid solution range has also been found for Nd 2 Co 17 , Si 4 . This isothermal section consists of 26 three-phase and four two-phase regions.

CRYSTAL-STRUCTURE AND SUPERCONDUCTIVITY OF NEW PB-BASED 1222-CUPRATE (PB0.5CD0.5)(SR0.9EU0.1)(2)(EU0.7CE0.3)(2)CU2O9+DELTA

A new superconductor (Pb0.5Cd0.5)(Sr0.9Eu0.1)(2)(Eu0.7Ce0.3)(2)Cu2O9+delta has been prepared. The compound has higher T-c values when it is synthesized in Oz than in air. Besides, the O-2-synthesized sample exhibits metallic behaviour, while the air-synthesized sample exhibits semiconducting behaviour in their normal state. It has a typical metal-insulator transition with the increase of the carrier concentration, which is proven by our calculation results of the bond valence sums of the Cu ions in the conducting CuO2 planes. (Pb0.5Cu0.5)(Sr7/8Eu1/8)2(Eu3/4Ce1/4)2Cu(2)O(9) is an analogous compound of (Pb,Cd)-1222. (Pb,Cd)-1222 has higher superconducting transition temperatures than (Pb,Cu)-1222. This difference can be explained from the viewpoint of charge transfer between the charge reservoir (Pb,Cu)O layers and the conducting CuO2 planes. The crystal structure of (Pb0.5Cd0.5)(Sr(0.9)Eu0. I)(2)(Eu0.7Ce0.3)(2)Cu2O9+delta has been refined by the Rietveld method. The refinement results indicate that both (Pb, Cd) and O(3) in the (Pb, Cd)O layer are displaced from their ideal sites.

Analysis of the interfaces of [NiFe/Mo](30) and [Fe/Mo](30) multilayers

The interface states of [NiFe/Mo](30) and [Fe/Mo](30) multilayers have been investigated by x-ray small angle reflection and diffuse scattering. Significant interface roughness correlation was observed in both ultrathin [NiFe/Mo](30) and [Fe/Mo](30) multilayers. An uncorrelated roughness of about 27-3.1 Angstrom was revealed in the [NiPe/Mo](30) multilayers, which is explained as originating from a transition layer between the NiFe and the Mo layers. By the technique of diffuse scattering, it is clearly indicated that the interfacial roughness of NiFe/Mo is much smaller than that of Fe/Mo although the lattice mismatch is the same in both multilayers.

The effect of Cu doping in the NiO2 plane on the stripe phase in La1.67Sr0.33NiO4

The effect of Cu doping on the stripe-ordered state in La1.67Sr0.33NiO4 has been studied by means of electrical resistivity and magnetic measurements and transmission electron microscopy observation. The investigations reveal that Cu doping at Ni sites does not change the modulation pattern of the charge ordering, but clearly reduces the charge-ordered-transition and spin-ordering temperatures. Moreover, Cu on the NiO2 planes tends to melt the stripe lattice and reduce the charge and spin stripe correlation lengths. These effects could arise from the cooperative action of carrier mobility enhancement, strong interplay of Cu spins with the host Ni spin-lattice system, and the disordering effect of Cu dopants.

Characterization of a new Pb-based 1222 cuprate Pb(Sr1.2La0.8)Gd2Cu2O9.06

A new compound Pb(Sr(1.2)L(0.8))Gd2Cu2O9.06 has been synthesized and characterized in this letter. The Pb ions in the rock-salt-type monolayer of this compound occur in the form of mixed valence states, i.e., Pb4+ and Pb2+, and the average cationic valence is 3.14, close to that in (Pb0.5Cd0.5)Sr2YCu2O7. It seems to us that the single-Pb-layer Pb-based layered compounds are stable only when the average cationic valence in this layer is close to three. The crystal structure refinement results indicate that the PbO layer is highly distorted, and no Cu ions enter this monolayer. The high distortion of the PbO layer makes the Pb-1222 phase preferentially orientate more readily. This compound does not superconduct. The nonsuperconductivity is not caused by low charge carrier concentration. It may be caused by the Gd2O2 layers, which affect not only the buckling degree of conducting CuO2 planes but the coupling effect between adjacent CuO2 planes as well.