Gc Che

Phase diagram of the BaOCuOY2O3 system and the relationship between composition and superconductivity

Abstract The phase diagram of the BaYCuO ternary system was determined. In the CuO-rich region, two compounds were obtained: Ba 2 YCu 3 O 9− y and Y 2 CuBaO 5 . Ba 2 YCu 2 O 9− y is a high T c superconductor ( T c ≈ 90 K). The relationship between composition and superconductivity was studied, and the most suitable technique for superconductor preparation was determined.

Mössbauer studies on novel high-Tc (Sn,Sr)-doped La2−2xSr2xCu1−xSnxO4 superconductors

Abstract For La 2−2 x Sr 2 x Cu 1− x Sn x O 4 ( x =0.075, 0.090 and 0.110) superconductors, the effects of Sn-doping on local microstructure is studied by means of Mossbauer spectroscopy. The results show that Sn ions in the 4+ valence state dominantly occupy Cu sites rather than La(Sr) site. In the view of the effective oxygen content (or excess oxygen), the dual role of Sn dopant on the carrier concentration is discussed. We attempt to explain the high transition temperature T c in (Sr,Sn)-doped La 2−2 x Sr 2 x Cu 1− x Sn x O 4 samples under the model of amphoteric effect of Sn-doping on the concentration.

Composition and superconductivity in Bi-Sr-Ca-Cu-O and substituted systems

The composition of the superconducting phase Bi4(Sr3±xCa3∓x)Σ=6Cu4O16, has been determined by means of a sysmetic investigation of the relationship between composition and superconductivity, and phase analysis. The superconducting phase belongs to tetragonal system witha=0.3825 nm,c=3.082 nm, space group (S.G.) 14/mmm. The effect of strontium and calcium contents in the Bi(Sr1±xCa1∓x)Σ=2Cu2O5.5, system and substitution in the Bi1−xAxSrCaCu2O5 (A=V, Gd, Y) and BiSrCa1−xPbxCu2O5.05 systems on superconductivity, have been investigated. In the Bi-Sr-Ca-Cu-O system, there are two superconducting phases corresponding to transition temperatures of 110 and 80 K, respectively. The difference between the two superconducting phases may be due to the stacking difference of atoms along thec direction in the structure and their oxygen content.

The effects of sulphur substitution on Y(Ba,Sr)2Cu2.5B0.5Oz systems

Abstract A series of doped compounds Y(Ba,Sr) 2 Cu 2.5 B 0.5− x S x O z (0 ⩽ × ⩽ 0.5) were synthesized by the solid state reaction method. The effects of sulphur doping on crystal structure as well as superconductivity in these samples were studied. An interesting phenomenon can be observed that superconductivity is destroyed at low doping level of sulphur (× ⩽ 0.2) and is induced again as doping level of sulphur increases ( x ⩾ 0.3) in the YBaSrCu 2.5 B 0.5− x S x O z (0 ⩽ × ⩽ 0.5) series. An initial explanation related to the large difference between B 3+ and S 6+ was made to interpret this experimental fact. The possibility of inducing extra hole concentration by substituting [BO 3 ] 3− with [SO 4 ] 2− groups and thus improving superconductivity was also discussed. These result may give new evidence for doping mechanism of substitution among oxyanion groups.