Growth, structure and physical properties of single crystals of pure and Pb-doped Bi-based high Tc superconductors
- 作者：E. Giannini ; R. Gladyshevskii ; N. Clayton ; N. Musolino ; V. Garnier ; A. Piriou ; R. Flü ; kiger
- 关键词：Bi-2223 ; Crystals ; Structure ; Superconductors
- 刊名：Current Applied Physics
- 出版年：2008
- 期刊代码：15_15671739
- 类别：ph
- 出版时间：March 2008
- 卷：8
- 期：2
- 页码：115-119
- 文件大小：580 K
摘要
Single crystals of (Bi1−xPbx)2Sr2Ca2Cu3O10+δ (x = 0 and 0.16) (sizes up to 3 × 2 × 0.1 mm3) have been grown by means of a newly developed “vapour-assisted travelling solvent floating zone” technique (VA-TSFZ). Post-annealing under high pressure of O2 (up to 10 MPa at T = 500 °C) was applied to enhance Tc (up to 111 K) and improve the homogeneity of the crystals (ΔTc 
1 K). The structure of both Pb-free and Pb-doped Bi-2223 was refined for the first time from single crystal X-ray diffraction (XRD) data. The unit cell of the average structure is pseudo-tetragonal with a = 5.4210(7), b = 5.4133(6) and c = 37.010(7) Å, and a = 5.395(1), b = 5.413(1) and c = 37.042(11) Å, for the Pb-free and the Pb-doped phase, respectively. An incommensurate modulation in the direction of one of the short cell vectors has been defined (q 
0.21 a*), however, the structure can be conveniently described in a supercell with a fivefold volume (a = 27.105(4) Å). With respect to the “non-modulated” structure, one additional oxygen atom for ten initial O was found to be inserted into the BiO layers. The superconducting anisotropy of Bi-2223 was found to be 50, from measurements of the lower critical field. The anisotropy of Bi-2223 is significantly reduced compared to that of Bi-2212, and this accounts for the enhanced irreversibility fields in Bi-2223. Furthermore, Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, which are both signatures of more effective pinning in Bi-2223 due to its reduced anisotropy.
1 K). The structure of both Pb-free and Pb-doped Bi-2223 was refined for the first time from single crystal X-ray diffraction (XRD) data. The unit cell of the average structure is pseudo-tetragonal with a = 5.4210(7), b = 5.4133(6) and c = 37.010(7) Å, and a = 5.395(1), b = 5.413(1) and c = 37.042(11) Å, for the Pb-free and the Pb-doped phase, respectively. An incommensurate modulation in the direction of one of the short cell vectors has been defined (q 0.21 a*), however, the structure can be conveniently described in a supercell with a fivefold volume (a = 27.105(4) Å). With respect to the “non-modulated” structure, one additional oxygen atom for ten initial O was found to be inserted into the BiO layers. The superconducting anisotropy of Bi-2223 was found to be 50, from measurements of the lower critical field. The anisotropy of Bi-2223 is significantly reduced compared to that of Bi-2212, and this accounts for the enhanced irreversibility fields in Bi-2223. Furthermore, Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, which are both signatures of more effective pinning in Bi-2223 due to its reduced anisotropy.