ISSN:
1434-6036
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Physik
Notizen:
Abstract In this article, the crystal structure and superconductivity of a new superconducting phase TlBa2CaCu2O6.5 (T c =72.5 K) in Tl−Ba−Ca−Cu−O system are studied. The crystal structure of the compound TlBa2CaCu2O6.5 has been determined by means of X-ray powder diffraction method. It belongs to primary tetragonal lattice with lattice parameters:a=3.847 Å,c=12.73 Å. Its space group isD 4h 1 −P4/mmm. Each unit cell contains one formular unit. The arrangements of ions in a unit cell are following: 1 Ca, and 1 Tl cations occupy 1(a) and 1(d) equivalent point positions respectively. 2 Cu cations occupy 2(h) (z=0.127) equivalent point positions. 2 Ba cations occupy 2(g) (z=0.281) equivalent point positions. 6.5 O anions respectively occupy 1(b), 2(h) (z=0.281) and 4(i) (z=0.127) equivalent point positions. Occupation factor is 0.929. The crystal structure of TlBa2CaCu2O6.5 is quite similar to those of the other superconducting phases in Tl−Ba−Ca−Cu−O system. All cations are distributed at positions of (0, 0,z) and (1/2, 1/2,z) alternately. The oxygen deficient pseudo-perovskite unit Ba−Cu−Ca−Cu−Ba is separated two Tl−O layers in the crystal structure of Tl2Ba2CaCu2O8. However, the oxygen deficient pseudo-perovskite unit Ba−Cu−Ca−Cu−Ba is separated by single Tl−O layer in the crystal structure of TlBa2CaCu2O6.5. The relations among the crystal structures of the superconducting phases as well as the relation between the crystal structure and superconductivity are discussed.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF01312148
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