C. Dong

Synthesis and crystal structure of new rare-earth copper oxyselenides: RCuSeO (R=La, Sm, Gd and Y)

A new series of copper oxyselenides RCuSeO (R=La, Sm, Gd and Y) have been prepared and studied by X-ray powder diffraction. The Sm-containing phase was determined to have a tetragonal crystal structure with the lattice parameters a=3.9512(1)A and c=8.7157(2)A, the space group of which is P4/nmm. Its structure is built of a fluorite type layer [Sm2O2] and an anti-fluorite type layer [Cu2Se2] stacking alternatively along c direction. The similarity of the diffraction patterns for the samples with R=La, Gd and Y to that of SmCuSeO suggests their assuming the same crystal structure.

Synthesis and crystal structure of barium copper fluochalcogenides:[BaCuFQ (Q=S,Se)]

Abstract Two new copper fluochalcogenides BaCuFQ (Q=S,Se) have been synthesized. They crystallize in a tetragonal crystal structure with space group P4/nmm and lattice parameters a =4.1230(1) A , c =9.0327(2) A for BaCuFS and a =4.2391(1) A , c =9.1217(2) A for BaCuFSe. The structure can be viewed as the intergrowth of a fluorite type layer [Ba 2 F 2 ] and an anti-fluorite type layer [Cu 2 Q 2 ].

Synthesis of the superconductors HgBa2CaCu2O6+δ and HgBa2Ca2Cu3O8+δ

Abstract The superconductors HgBa 2 CaCu 2 O 6+δ and HgBa 2 Ca 2 Cu 3 O 8+δ (denoted 1212 and 1223) were prepared at temperatures below 750°C from simple oxides without using precursors. The latter one forms at a higher temperature and needs a longer calcinating time. After oxygen annealing the T c for the 1223 phase increases with about 15 K from 118 to 133 K, while that of the 1212 phase changes only little.

Superconductivity at 30 K in the Nd2CuO4-type cuprate Tm1.83Ca0.17CuO4

Abstract The Nd 2 CuO 4 -type Ca-doped rare-earth cuprates R 1.83 Ca 0.17 CuO 4 (R=Gd, Dy or Tm) have been synthesized under high pressure. Only that with the small ion Tm 3+ and thus the short CuO bonds (1.916 A) was superconducting (at about 30 K). This was considered to be the first example of p-type superconductivity in the purely square-planar CuO 2 layers without apical oxygens.

The effects of composition, synthesis conditions, oxygen content and F doping on superconductivity and structure for R-substituted Bi-2201

The effects of composition, synthesis conditions, oxygen content and F doping on superconductivity and structure for the R-substituted Bi-2201 compound was investigated by means of XRD and measurements of superconductivity. For the compound (R = La, Pr, Nd and Sm), the optimum value of x for is x = 0.4. When x = 0.4, the optimum sintering temperature is for R = La, Pr and Nd, for R = Sm. decreases with decreasing ionic radius of R. For , the optimum range of oxygen content is y = 0.28 - 0.33 and the superconductivity is improved by quenching. For F-doped Bi-2201, decreases with increasing F 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.

Synthesis and crystal structure of copper oxybromides [M2Cu3O4Br2 (M=Sr,Ba)]

Abstract Two new members of copper oxybromides M 2 Cu 3 O 4 Br 2 (M=Sr,Ba) have been prepared and studied by X-ray powder diffraction. They were determined to assume a tetragonal crystal structure with space group 14/mmm and lattice parameters a =5.4840(2) A , c =13.297(1) A for Sr 2 Cu 3 O 4 Br 2 and a =5.5386(2) A , c =14.624(1) A for Ba 2 Cu 3 O 4 Br 2 . The structure is built of the sheets [Cu 3 O 4 ] and the fluorite-type layers [M 2 Br 2 ] stacking alternatively along [001]. The [Cu 3 O 4 ] layer can be described as the well-known sheets [CuO 2 ] in cuprate superconductors with the addition of Cu to the centers of the square units [CuO 2 ] at a period of √2a p ×√2 a p . In the alkaline-earth copper oxyhalide systems, M 2 CuO 2 X 2 can be obtained only with the low ionic radius sum r M + X of M 2+ and X − , while M 2 Cu 3 O 4 X 2 was got only with a high r M + X where M=Ca,Sr,Ba and X=Cl,Br.

Ca doped YBaSrCu2.5B0.5−xSxOz series: combination effect of the cation and oxyanion doping

Abstract A series of compounds (Y0.6,Ca0.4)BaSrCu2.5B0.5−xSxOz (0.0≤x≤0.5) were synthesized using the solid state reaction method. The effects of calcium substitution on phase composition and crystal structure and superconductivity are studied. The combination of the cation and oxyanion substitutions, Y3+ by Ca2+ and [BO3]3− by [SO4]2−, can easily induce superconductivity and Tc increase of 39–43 K can be obtained in the series. Compared with related Ca-free series, we can draw the conclusion that the combination of cation and oxyanion doping is superior to single doping in hole providing ability.

Effect of quenching on the superconductivity and oxygen content of Bi(Pb)-2223 phase

Abstract The effect of quenching on the superconductivity and oxygen content of Bi(Pb)-2223 phase has been investigated by means of XRD TEM TGA and oxygen content and superconductivity measurements. The results indicated that T c(0) exhibits a nonlinear change with raising quenching temperature(T Q ), in the range of 100–400°C, T c(0) unchange approximately, T Q =500−600° C , it increases lightly, at 750°C, it exhibits a minimum value. The oxygen content is increased in the sample quenched at 500–600°C and the weak link behavior is improved when T Q =800–820° C . Bi 1.7 Pb 0.3 Sr 2 Ca 2 Cu 3 O 10+δ superconductor with Tc near 110K has a optimum oxygen content, δ =0.14–0.29.

Stability of the infinite layer SrCuO2 studied by high temperature X-ray diffraction

Abstract The stability of the infinite layer SrCuO 2 upon heating in air has been investigated by the high temperature X-ray diffraction method. The infinite layer SrCuO 2 first reacted gradually with CO 2 in air to form SrCO 3 when the temperature was above 300°C. When the temperature was over 400°C, the infinite layer SrCuO 2 transformed into orthorhombic SrCuO 2 . The lattice parameters a and c of the infinite layer SrCuO 2 showed different thermal expansion coefficients, i.e., da/dT = 3.392×10 −5 A /°C and dc/dT = 5.80×10 −5 A /°C .