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Journal ArticleDOI

Superconductivity studies on TlMBaCuO (M = Ce, Th, Pr, Tb, Pb, and Te) system☆

01 Sep 1990-Journal of Solid State Chemistry (Academic Press)-Vol. 88, Iss: 1, pp 177-182
Abstract: Superconductivity with a T{sub c,zero} at 75 {plus minus} 1 K has been observed in Tl-M-Ba-Cu-O (M = Ce, Th) system for a starting nominal composition of Tl{sub 2.2}M{sub 1}Ba{sub 2}Cu{sub 3}O{sub y}. X-ray data show that the compounds are multiphasic with the 2,201 phase as the predominant one which is responsible for superconductivity. Lower T{sub c} values are noted for M = Pr and Tb. Only metallic behavior is observed for pure Tl{sub 2}Ba{sub 2}Cu{sub 1}O{sub y} and M = Pb or (Pb + Sb) or Te containing phases down to 15 K.

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Journal ArticleDOI
01 Jan 1990-

Journal ArticleDOI
K.A. Thomas1, U.V. Varadaraju1, G.V. Subba Rao1, C.V. Tomy2  +1 moreInstitutions (2)
Abstract: Superconductivity with a maximumTc, zero of 58 K forx > 0·75 has been observed in a nominal starting composition, ThxTl2Sr2Ca2Cu3Oy. X-ray data show that the 1212 phase gets stabilized due to part substitution of Th at the Tl-site forx⩾0·25; however,Tc is low forx<0·75.

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References
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Journal ArticleDOI
Z.Z. Sheng1, Allen M. Hermann1Institutions (1)
01 Mar 1988-Nature
Abstract: The discovery of 30-K superconductivity in the La–Ba–Cu–O system1 and 90-K superconductivity in the Y–Ba–Cu–O system2 stimulated a worldwide search for even higher-temperature superconductors. Unfortunately, most of the higher-temperature transitions reported in the past year have proved to be unstable, irreproducible, or not due to bulk superconductivity3–7. Recently, we and co-workers8,9 reported superconductivity above 90 K in a new Tl–Ba–Cu–O system, and pointed out that elemental substitutions in this system may lead to even higher-temperature superconductivity. Here we report stable and reproducible bulk superconductivity with an onset at 120 K and zero resistance above 100 K in the Tl–Ca/Ba–Cu–O system. This transition temperature is much higher than those observed for typical rare-earth-containing superconductors, and the onset temperatures are comparable to that in the Bi–Ca/Sr–Cu–O system, as reported in refs 10 and 11 (received after submission of this paper).

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893 citations


Journal ArticleDOI
Z.Z. Sheng1, Allen M. Hermann1Institutions (1)
01 Mar 1988-Nature
Abstract: The initial discovery by Bednorz and Muller1 of 35-K superconductivity in the La-Ba-Cu-O system has stimulated worldwide activity in searching for higher-temperature superconductors. Elemental substitution has proved to be most effective in raising transition temperature. Substitution of Sr for Ba has produced 40-K superconductivity2–5and substitution of Y for La has produced a new high-temperature superconductor with transition temperature above liquid-nitrogen temperature6. A class of superconducting compounds of the form RBa2Cu307-x has been explored by further substitutions of other rare earths (Y is considered in the rare-earth [RI category here) for Y7-13. To date, a rare earth, an alkaline earth, copper and oxygen have been required for all high-temperature superconductors14,15. (Zhanget al 14reported 90-K superconductivity in the Th-Ba-Pb(Zr)-Cu-O system. Panetal15reported 50-K superconductivity in the Y-Ba-Ag-O system. As Th is a member of the actinide series which belongs to the same Group 3B in the periodic table as the lanthanide series and Ag belongs to the same Group 1B as Cu, high-temperature supercon-ductors are still thought to be closed in the Group 3B—Group 2A-Group 1B—oxygen system. ) Only partial substitutions ha. e led to superconductors, but with no significant rise of transition tem-perature (the only exception is 40-K superconductivity in La2CuO4-x , refs 16, 17). Here we report superconductivity in the rare-earth-free TI-Ba-Cu-O system. We have obsened sharp drops of resistance starting above 90 K with zero resistance at 81 K in this system. Magnetic measurements have confirmed that these sharp drops of resistance in the TI-Ba-Cu-O samples origi-nate from superconductivity. The samples are stable in air for at least two months, and their preparation is easily reproduced.

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634 citations


Journal ArticleDOI
01 Jul 1988-Physical Review B
TL;DR: The Tl-O layers are much more strongly bound to each other than are the Bi-O layer; thus, better conduction along the c axis is expected for Tl/sub 2/Ba/ sub 2/CuO/sub 6/ relative to Bi/sub 1/Sr/sub 3/Cu-O-sub 6/.

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Abstract: The structures of ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$Cu${\mathrm{O}}_{6}$ and ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$Cu${\mathrm{O}}_{6}$ have been solved and refined from single-crystal x-ray diffraction data. The structures are essentially the same and have single Cu-O sheets separated by either Tl-O or Bi-O double layers. The ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$Cu${\mathrm{O}}_{6}$ structure is tetragonal with $a=3.87$ \AA{} and $c=23.24$ \AA{}, and there are strictly flat Cu-O sheets. ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$Cu${\mathrm{O}}_{6}$ has a lower-symmetry structure which may be approximated with an orthorhombic cell with $a=5.36$ \AA{}, $b=5.37$ \AA{}, and $c=24.62$ \AA{}; however, this ignores superstructure reflections along both the $a$ and $c$ axes. The Tl-O layers are much more strongly bound to each other than are the Bi-O layers; thus, better conduction along the $c$ axis is expected for ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$Cu${\mathrm{O}}_{6}$ relative to ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$Cu${\mathrm{O}}_{6}$. Superconducting transition temperatures of 9 and 90 K were observed for ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$Cu${\mathrm{O}}_{6}$ and ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$Cu${\mathrm{O}}_{6}$, respectively.

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310 citations


Journal ArticleDOI
Stuart S. P. Parkin1, V. Y. Lee1, A. I. Nazzal1, R. Savoy1  +3 moreInstitutions (1)
01 Oct 1988-Physical Review B
TL;DR: Variations in the transition temperatures in the double- and triple-CuO/sub 2/-layer compounds are observed to correlate with increased densities of intergrowths of related structures.

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Abstract: We describe the structures and superconducting properties of six compounds in the Tl-Ca-Ba-Cu-O system of the general form, Tl/sub m/Ca/sub inr-1/Ba/sub 2/Cu/sub n/O/sub 2(//sub n//sub +1)+//sub m/, where m = 1 or 2 and n = 1, 2, or 3. One of these compounds displays the highest known superconducting transition temperature, T/sub c/approx. =125 K. The structures of these compounds consist of copper perovskitelike blocks containing 1, 2, or 3 CuO/sub 2/ planes separated by one or two Tl-O layers and thus form a model family of structures in which both the size and separation of the copper oxide blocks can be independently varied. The superconducting transition temperature increase with the number of CuO/sub 2/ planes in the perovskitelike block for both the Tl-O monolayer and bilayer compounds. For each pair of compounds (m = 1,2) with the same number of CuO/sub 2/ planes (same n), the transition temperatures are similar but are consistently 15--20 K lower in the material with single Tl-O layers. Variations in the transition temperatures in the double- and triple-CuO/sub 2/-layer compounds are observed to correlate with increased densities of intergrowths of related structures.

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223 citations


Journal ArticleDOI
01 Oct 1988-Physical Review B
Abstract: The structures of ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$Ca${\mathrm{Cu}}_{2}$ ${\mathrm{O}}_{8}$ and ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{2}$ ${\mathrm{Cu}}_{3}$${\mathrm{O}}_{10}$ were refined from neutron-powder-diffraction data. The data for ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$Ca${\mathrm{Cu}}_{2}$ ${\mathrm{O}}_{8}$ were taken at 298 K, and the data for ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{2}$ ${\mathrm{Cu}}_{3}$${\mathrm{O}}_{10}$ were obtained at both 150 and 13 K. The results are essentially in agreement with the structural refinements based on single-crystal x-ray-diffraction data and confirm the positional disorder of the oxygen atoms in the Tl-O planes. The low-temperature refinements for ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{2}$ ${\mathrm{Cu}}_{3}$${\mathrm{O}}_{10}$ indicate that the symmetry remains tetragonal down to 13 K and that there is no significant structural change or discontinuity in the cell parameters through the superconducting critical temperature near 125 K.

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131 citations