Crystal Structure of Tl2Ba2Ca2Cu3O10, a 125 K Superconductor
29 Apr 1988-Science (American Association for the Advancement of Science)-Vol. 240, Iss: 4852, pp 631-634
TL;DR: Electron microscopy in the Tl/Ba/Ca/Cu/O system has revealed intergrowths where n = 5; such regions may well be responsible for the superconducting onset behavior observed in this system at about 140 K.
Abstract: There is now a new series of high-temperature superconductors that may be represented as (A(III)O)(2)A(2)(II)Can-1CunO2+2n where A(III) is Bi or Tl, A(II) is Ba or Sr, and n is the number of Cu-O sheets stacked consecutively. There is a general trend toward higher transition temperatures as n increases. The highest n value for a bulk phase is three and is found when A(III) is Tl. This compound, Tl(2)Ba(2)Ca(2)Cu(3)O(10), has the highest transition temperature( approximately 125 K) of any presently known bulk superconductor. The structure of Tl(2)Ba(2)Ca(2)Cu(3)O(10) has been determined from single-crystal x-ray diffraction data and is tetragonal, with a = 3.85 A and c = 35.9 A. No superstructure is observed, and the material is essentially twin-free. Electron microscopy in the Tl/Ba/Ca/Cu/O system has revealed intergrowths where n = 5; such regions may well be responsible for the superconducting onset behavior observed in this system at about 140 K.
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TL;DR: In this paper, a review of the results of the density-functional type of electronic structure calculations is presented, and their results are compared with the relevant experimental data, showing that the important electronic states are dominated by the copper and oxygen orbitals, with strong hybridization between them.
Abstract: Since the discovery of superconductivity above 30 K by Bednorz and M\"uller in the La copper oxide system, the critical temperature has been raised to 90 K in Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and to 110 and 125 K in Bi-based and Tl-based copper oxides, respectively. In the two years since this Nobel-prize-winning discovery, a large number of electronic structure calculations have been carried out as a first step in understanding the electronic properties of these materials. In this paper these calculations (mostly of the density-functional type) are gathered and reviewed, and their results are compared with the relevant experimental data. The picture that emerges is one in which the important electronic states are dominated by the copper $d$ and oxygen $p$ orbitals, with strong hybridization between them. Photon, electron, and positron spectroscopies provide important information about the electronic states, and comparison with electronic structure calculations indicates that, while many features can be interpreted in terms of existing calculations, self-energy corrections ("correlations") are important for a more detailed understanding. The antiferromagnetism that occurs in some regions of the phase diagram poses a particularly challenging problem for any detailed theory. The study of structural stability, lattice dynamics, and electron-phonon coupling in the copper oxides is also discussed. Finally, a brief review is given of the attempts so far to identify interaction constants appropriate for a model Hamiltonian treatment of many-body interactions in these materials.
988 citations
TL;DR: Those oxides that superconduct at the highest temperatures contain copper-oxygen sheets; however, other elements such as bismuth and thallium play a key role in this new class of superconductors.
Abstract: Spectacular advances in superconductors have taken place in the past two years. The upper temperature for superconductivity has risen from 23 K to 122 K, and there is reason to believe that the ascent is still ongoing. The materials causing this excitement are oxides. Those oxides that superconduct at the highest temperatures contain copper-oxygen sheets; however, other elements such as bismuth and thallium play a key role in this new class of superconductors. These superconductors are attracting attention because of the possibility of a wide range of applications and because the science is fascinating. A material that passes an electrical current with virtually no loss is more remarkable when this occurs at 120 K instead of 20 K.
532 citations
TL;DR: In this article, the authors reported the growth of small single crystals of this phase, with composition (Ca 0.86Sr0.14)CuO2, and their characterization by single-crystal X-ray diffraction.
Abstract: Oxide superconductors in the system Tl2Ba2Can–1CunO4+2n (ref. 1) have transition temperatures (Tc) above 100 K, increasing with n. So far, stacking sequences up to n = 3 have been found in small crystals, and sequences with n > 3 have been seen in electron microscopy studies1. For large n, the stoichiometry of Tl2Ba2Can–1CunO4+2n approaches CaCuO2, a structure expected to consist only of CuO2 planes separated by Ca atoms. By analogy with Tl2Ba2Can–1CunO4+2n, the unit cell of this hypothetical phase is expected to be tetragonal with a = 3.86 A. Such a compound is not known in the Ca–Cu–O system, but Roth2 recently reported that small amounts of Sr on the Ca site can stabilize this simple structure. Here we report the growth of small single crystals of this phase, with composition (Ca0.86Sr0.14)CuO2, and their characterization by single-crystal X-ray diffraction. The crystals are tetragonal with space group P4/mmm, and the structure contains planar [CuO2]∞ layers separated by Ca and Sr atoms. The structure is a simple defect perovskite with ordered oxygen vacancies and can be regarded as the n = ∞ parent of the A2B2Can–1CunO4+2n (A = Bi, Tl; B = Sr, Ba) superconductors.
514 citations
TL;DR: In this paper, a number of models for the modulation in the title compounds are postulated and the best agreement with experimental data is obtained for the model with extra oxygen in the BiO layers.
Abstract: A number of models for the modulation in the title compounds are postulated. For the Bi compounds periodic changes are considered due to the following structural models: (a) extra oxygen in the BiO layers, (b) partial substitution of Sr by a vacancy, (c) partial substitution of Bi by Cu, and (d) changes in the orientations of the lone pairs of Bi. Computer calculated images for these models are compared with high resolution images. Also general structural considerations and structural details from the reported subcells are taken into account. It is concluded that the best agreement with experimental data is obtained for the model with extra oxygen in the BiO layers. Several performed experiments, which support this conclusion, are reported and discussed; the most important of which are the existence of solid solutions Bi2Sr2−xBaxCuO6+δ, with x
325 citations
TL;DR: New high-temperature superconductors based on oxides of thallium and copper, but not containing barium, have been prepared with structure refinement carried out with single-crystal x-ray diffraction data.
Abstract: New high-temperature superconductors based on oxides of thallium and copper, but not containing barium, have been prepared. A transition temperature (T(c)) of about 85 K is found for (Tl(0.5)Pb(0.5)) Sr(2)CaCu(2)O(7) whereas (Tl(0.5)Pb(0.5))Sr(2)Ca(2)Cu(3)O(9) has a T(c) of about 120 K. Both materials possess tetragonal symmetry with a = 3.80 A, c = 12.05 A for (Tl(0.5)Pb(0.5))Sr(2)CaCu(2)O(7), and a = 3.81 A, c = 15.23 A for (Tl(0.5)Pb(0.5))Sr(2)Ca(2)Cu(3)O(9). A structure refinement of the latter phase has been carried out with single-crystal x-ray diffraction data.
303 citations
References
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TL;DR: In this paper, a new high-Tc oxide superconductor of the BiSrCa-Cu-O system without any rare earth element was discovered, which has Tc of about 105 K, higher than that of YBa2Cu3O7 by more than 10 K.
Abstract: We have discovered a new high-Tc oxide superconductor of the Bi-Sr-Ca-Cu-O system without any rare earth element. The oxide BiSrCaCu2Ox has Tc of about 105 K, higher than that of YBa2Cu3O7 by more than 10 K. In this oxide, the coexistence of Sr and Ca is necessary to obtain high Tc.
2,698 citations
TL;DR: In this paper, 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 was reported.
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).
910 citations
TL;DR: In this paper, the origin of the orthorhombic-tetragonal transition and the importance of the Cu-O chains for superconductivity is discussed. But the behavior of these materials with respect to magnetic impurities is apparently different from conventional Bardeen-Cooper-Schrieffer-type superconductors, and any new mechanism proposed must be mostly sensitive to local structural disorder.
Abstract: The mixed ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{M}}_{\mathrm{x}}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{y}}$ (M=Ni, Zn, Fe, Co, and Al) phases have been characterized for their structural, magnetic, and superconducting properties. The oxygen content in these phases is dependent on the nature and the amount of doping, especially for Co and Fe. The material remains orthorhombic when Cu is replaced by Ni or Zn whereas it evolves to tetragonal symmetry for the Fe-, Co-, and Al-doped compounds when x exceeds 0.05. Evidence for the major substitution of Co in the Cu-O chains only is obtained by means of thermogravimetric analysis and neutron diffraction measurements. The room-temperature M\"ossbauer spectra of the Fe-doped compounds consist of three doublets; their site assignments are proposed. dc resistance and ac susceptibility have shown that both magnetic and diamagnetic ions destroy ${T}_{c}$ in a similar manner. At x=0.2 the Fe and Co compounds are tetragonal, superconduct at 50 K, and show a Curie-type magnetic behavior associated with a magnetic moment of 3.4${\ensuremath{\mu}}_{B}$ per doping atom. The origin of the orthorhombic-tetragonal transition and the importance of the Cu-O chains for superconductivity is discussed. The behavior of these materials with respect to magnetic impurities is apparently different from conventional Bardeen-Cooper-Schrieffer-type superconductors, and we believe that any new mechanism proposed must be mostly sensitive to local structural disorder.
670 citations
TL;DR: In this paper, the authors reported superconductivity in the rare earth-free TI-Ba-Cu-O system with a resistance starting at 90 K with zero resistance at 81 K.
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.
645 citations
TL;DR: A new superconductor that displays onset behavior near 120 K has been identified as Bi2Sr3-xCaxCu2O8+y, with x ranging from about 0.4 to 0.9, and electron microscopy studies show an incommensurate superstructure along the a axis that can be approximated by an increase of a factor of 5 over the subcell dimension.
Abstract: A new superconductor that displays onset behavior near 120 K has been identified as Bi2Sr3-xCaxCu2O8+y, with x ranging from about 0.4 to 0.9. Single crystal x-ray diffraction data were used to determine a pseudo-tetragonal structure based on an A-centered orthorhombic subcell with a = 5.399 A, b= 5.414A, and c = 30.904 A. The structure contains copper-oxygen sheets as in La2CuO4 and YBa2Cu3O7, but the copper-oxygen chains present in YBa2Cu3O7 do not occur in Bi2Sr3-xCaxCu2O8+y. The structure is made up of alternating double copper-oxygen sheets and double bismuth-oxygen sheets. There are Ca2+ and Sr2+ cations between the adjacent Cu-O sheets; Sr2+ cations are also found between the Cu-O and Bi-O sheets. Electron microscopy studies show an incommensurate superstructure along the a axis that can be approximated by an increase of a factor of 5 over the subcell dimension. This superstructure is also observed by x-ray diffraction on single crystals, but twinning can make it appear that the superstructure is along both a and b axes. Flux exclusion begins in our samples at about 116 K and is very strong by 95 K. Electrical measurements on a single crystal of Bi2Sr3-xCaxCu2O8+y show a resistivity drop at about 116 K and apparent zero resistivity at 91 K.
623 citations