High resolution synchrotron X-ray powder diffraction study of the structure of Tℓ2Ba2CaCu2O8

✍ Scribed by M. Eibschutz; L.G. Van Uitert; W.H. Grodkiewicz; D.E. Cox

• Publisher: Elsevier Science
• Year: 1989
• Tongue: English
• Weight: 139 KB
• Volume: 162-164
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(89)91140-4

✦ Synopsis

Polycrystalline material of approximate composition Te2Ba 2 Ca Cu2Os was synthesized by melting oxides together, pressing pellets and heating in sealed quartz tubes. High resolution synchrotron X-ray powder data obtained at beam-lineoXTA at the National Synchrotron Light Source revealed a tetragonal phase with a = 3.8545, c ----29.322A, and a few weak impurity peaks. Rietveld refinement based on space group I4/mmm gave results in essential agreement with those obtained in previous x-ray single crystal and neutron powder determinations, including appreciable positional disorder of the thallium and oxygen atoms in the Tt~-O planes. The refined site occupancies were found to be high for Ca and low for T~, consistent with partial substitution of the type (T~l.65Ca035)Ba2(Ca0 ssT~0 15)Cu208. However, the possibility that there is some Cu on the T~ sites cannot be excluded.

Recently there has been much interest in superconductors with superconducting transition temperatures (To) above 77K; these conductors do not contain rare earth elements. One such family of these high Tc superconductors consists of the T~-Ba-Ca-Cu-O compounds. 1 The superconducting compounds in the system T£-Ba-Ca-Cu-O have the general formula T£2Ba2 Can-1Cun 04n + 2, where n is the number of Cu-O layers stacked consecutively.