Thallium Cuprates Research Articles

Synthesis and characterization of Tl2BaCeCu2Oy

It has been reported that multi-elemental cuprates material creates chemical pressure that enhances superconductivity. It is not clear what phase transition it possesses at this state. The Tl2BaCeCu2Oy was prepared using a thermal treatment solid-state reaction technique. This technique is expected to optimize the crystalline properties of the sample. It was discover the particulate size and the mean roughness of the compound are 190.742 nm and 154.382 nm respectively. Also, aside Cu–O plane that is known as the charge reservoir for cuprates superconductor, the Cu-Tl plane is also a charge reservoir that could initiate superconductivity. This result shows that the mechanism of high temperature superconductors can be decipher because this experiment reveals that thallium cuprates was found to possess superconducting phase transitions in the third order.

ChemInform Abstract: Effect of Antimony on the Superconducting Properties of Yttrium, Bismuth, and Thallium Cuprates.

ChemInform Abstract: Effect of Antimony on the Superconducting Properties of Yttrium, Bismuth, and Thallium Cuprates.

Effects of magnetic impurity Co on stripe phase of (Bi/Tl) $_\mathsf2$ (Sr/Ba) $_\mathsf2$ CaCu $_\mathsf2$ O $_\mathsf{8+\delta}$ superconductors

The effects of Co impurity substitution at the Cu site of bilayer bismuth and thallium cuprates have been studied over a wide range of carrier concentration. For both the systems it is found that the suppression of the superconducting transition temperature, T c is more rapid in the underdoped region. No anomalous suppression of T c at p $\sim$ 1/8 (p is the hole concentration per Cu ion) is found for different Co concentrations. This indicates that magnetic impurity Co behaves differently with respect to pinning of dynamical stripes as was observed in the case of non-magnetic impurity Zn by Akoshima et al. [Phys. Rev. B 57, 7491 (1998)] in bilayer bismuth cuprate. Pseudogap magnitude (E g ) for each Co doping are observed to have a correspondence with a related characteristic temperature T * obtained from thermopower measurements where T * increases with increasing Co-concentration at a fixed carrier concentration. Both T * and E g are found to follow an inverse power law ( $\sim$ $\frac{1}{p^n}$ ) with different n values.

Effect of Zn and Mn substitutions on the formation and superconductivity of Tl-1212 type phase (Tl0.85Cr0.15)Sr2CaCu2O7

In order to stabilize the superconducting phase of the copper oxide based materials, elemental substitution method has been widely employed. The TlSr2CaCu2O7 (1212 type phase) in pure form has superconducting transition temperature (Tc) range from 0–80 K [1]. However, this phase is not easily prepared in pure form. Partial substitutions by other elements at various metal sites in this system can stabilize the 1212 phase and improve its superconducting properties [2–4]. In particular, single elemental substitution showed Tc of 80–90 K [2–6] and double elemental substitution is necessary to enhance Tc to above 100 K [7–10]. Only for Cr that a single substitution gives Tc above 100 K [11]. Cr substitution effectively replaces Tl between 10–20% to give the highest transition temperature up to 110 K [12]. The average valence of Cr in this superconductor is reported to be higher than +3. It has also been reported that in this material the Ca site can be partially occupied by Tl [12]. Local ordering of the chromate groups in this material has also been reported [13]. It is interesting to investigate further the effect of Cr substitution together with other elements on the superconductivity and formation of the 1212 phase. It is well known that most rare-earths are effective in stabilizing the 1212 phase. It is worthwhile to investigate the effect of elements other than the rare-earths, for example the transition metals, in the formation of the 1212 phase. In this letter we report the effect of partial substitution of Zn and Mn in (Tl,Cr)Sr2CaCu2O7. Mn substitution is of particular interest because it is multivalent (+2/+3/+4/+7). If Zn and Mn are in the +2 state, then there will be no change in the carrier concentration and the variation in Tc can be due to the change in volume fraction of the 1212 phase as a result of the substitution. If they exist in valence states other than +2, the variation in Tc may be due among others, to both the changes in volume fraction as well as the carrier concentration. Both elements may effect the bonding environment between the structural blocks of the thallium cuprates where lattice mismatch may occur. Samples with nominal starting composition (Tl0.85Cr0.15)Sr2(Ca1−x Mx )Cu2O7 with M=Zn and Mn were prepared via the solid state reaction using high purity oxide component (>99.99%) through the precursor method. Appropriate amounts of Sr2CO3, CaO, CuO and ZnO or MnO were mixed, ground and heated at

A Novel Mixed Valent Chromium-Layered Oxide with Peculiar Magnetic Properties: Sr4.5Cr2.5O9

A new mixed valent chromium-layered oxide, Sr4.5Cr2.5O9, with a structure closely related to the “0201–1201” structure of the superconducting cuprate TlBa2−xLa2+xCu2O9, has been synthesized at normal pressure. This orthorhombic phase (a=10.7959(2) Å, b=5.4012(1) Å, and c=30.0755(6) Å) consists of the regular intergrowth of [Sr2CrO4]0201 blocks and [(Sr0.5Cr0.5)Sr2CrO5]1201 blocks. It differs from the thallium cuprate by the 1:1 ordering of Sr and Cr species within the intermediate layer of the “1201” block, so that at this level CrO4 tetrahedra, containing Cr6+ species, are obtained. Moreover, at the boundary between the “1201” and “0201” blocks, CrO6 octahedra alternate with CrO5 pyramids, both occupied by Cr3+ species. The magnetic measurements show an original metamagnetic transition from an antiferromagnetic to a weak ferromagnetic state. These properties are interpreted in terms of strong intralayer and weak interlayer magnetic couplings between Cr3+ species through a superexchange mechanism.

A new thallium–strontium–lanthanum cobaltite

A general technique for the preparation of complex Tl–Sr–La cobaltites, via the interaction of a La 2−xSr xCoO 4−y precursor with Tl 2O 3 in a sealed gold ampoule was elaborated. It allowed obtaining the compound Tl 0.64Sr 1.5La 0.5CoO 5−ε, whose bulk and surface compositions were investigated by EPMA and ESCA, respectively. This new phase is isostructural with the 1201 member of the thallium cuprate series with tetragonal unit-cell parameters a = 3.781 Å, c = 8.697 Å. The specific features of the synthesis mechanism that result in kinetic limitations of the purity of the reaction product were analyzed. Various possibilities for accommodating the large observed thallium deficiency were considered regarding the complex structure of the oxide.

Impurity substitution in bismuth and thallium cuprates: suppression of Tc and estimation of pseudogap

Suppression of T c in bilayer bismuth and thallium cuprates by substitution of Co impurities at Cu sites were taken for examination. T c suppression data on differently doped Bi2212 and Tl2212 were analysed within the unitary pair-breaking formalism due to Abrikosov and Gorkov, by fitting data points to a phenomenological relation valid for weak coupling d-wave superconductors. Values of the pseudogap magnitude at each doping were thereby estimated within a “Fermi-level density of states suppression” picture. Pseudogap magnitude from our estimation was observed to have a correspondence with a related characteristic temperature T* obtained by thermoelectric power measurements. Effects of pseudogap on the density of states were studied by calculating the susceptibility, which shows a broad peak at high temperature. This peak feature in susceptibility is indicative of an unusual metallic state, which could be explored further by other systematic measurements.

Thallium cuprate 1223 type.: I. Its elaboration and dependence of chemical and thermal stability and of superconducting transition temperature on Tl/Pb and Sr/Ba substitutions

The formation of samples with nominal composition (Tl x Pb 1− x )(Sr 1− y Ba y ) 2Ca 2Cu 3O z was followed by X-ray diffraction study. With the chosen elaboration conditions, the 1223 phases were formed in two steps with a 1212 type phase observed as an intermediate compound. From the results, the limits of the 1223 single phase field were determined for temperature below 930°C and under 1 bar of oxygen. Samples with 91% purity were obtained and for compositions located outside the limits of the monophased field, a Tl/Pb–Sr/Ba-1212 and a substituted Tl/Pb and Sr/Ba perovskite were found as the main impurities.

A polarized x-ray absorption spectroscopy study of O K and Cu edges in a Tl(2212) thin film

A reliable estimate of the density of states having in-plane and out-of-plane symmetry in the O K-edge and the -edge polarized spectra is important for checking the validity of several theoretical models which predict an active role for these states in the mechanism of superconductivity. In the present contribution, we report on our fluorescence-yield O K-edge and -edge polarized spectra obtained for a well characterized and oriented overdoped Tl(2212) thin film as well as our simultaneous fluorescence- and total-yield measurements on an optimally doped Tl(2212) thin film. Our results show that a significant number of out-of-plane and holes also exist in thallium cuprates, more so in the overdoped case, and that use of the bulk-sensitive fluorescence technique is better for obtaining a reliable estimate of the density and symmetry of these holes. The spectra are compared with those reported earlier for other cuprate systems and are interpreted in terms of the available band-structure calculations. No direct correlation between superconductivity and the presence or absence of out-of-plane covalent and doping hole densities appears plausible, so theories based on the existence of a large density of such holes appear to be inconsistent with the experiment.

L'oxychromate Tl3(CrO4)Sr8Cu4O16: phénomènes d'ordre entre le thallium et le chrome

Long range ordering between chromium and thallium has been evidenced for the first time in copper oxychromate Tl3(CrO4)Sr8Cu4O16 using HREM, XRD and ND. This compound, which crystallizes in an orthorhombic cell with a = 3.7803(1) Å, b = 15.2573(2) Å and c = 17.6737(3) Å derives from the "1201" TlSr2CuO5 structure by replacing one thallium oxygen polyhedra out of four by one CrO4 group in an ordered way. The Mayn features that characterize this original structure deal with the waving character of the [CuO2]∞ layers, and the absolute planar character of the [(Tl,Cr)O]∞ layers. In the [(Tl,Cr)O]∞ layers, the thallium and oxygen atoms form triple ribbons of edge-sharing TlO4 tetrahedra and TlO6 octahedra running along a, whereas the CrO4 tetrahedra are displayed in rows running along a, but are disconnected from each other and from the other polyhedra in the layer. Two kinds of CuO6 octahedra are observed, whose distortions originate from their connection with different polyhedra along c. This superconductor, whose Tc can be raised to 34 K after argon-hydrogen annealing, exhibits a rather high superconducting volume fraction (> 40%) compared to other "1201" thallium cuprates.

Raman microprobe analysis of patterned Tl-2212 thin films

We have used MicroRaman spectroscopy to evaluate the effects of ion-milling on the exposed edges of patterned Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ (Tl-2212) lines. Raman microprobe has previously been used to evaluate oxygen loss at the edges of patterned YBCO lines. The results indicated that appreciable oxygen loss was caused by ion-milling under certain conditions. oxygen loss at the edges will decrease non-uniformly the effective width of the superconducting line. This can, in turn, impact the electrical characteristics of patterned devices. Using the 633 nm lined of a HeNe laser, we have measured the Raman spectrum scanning across patterned and unpatterned regions of several Tl-2212 films with a mapping stage. It is well known that the Raman peak at /spl ap/497 cm/sup -1/ corresponds to the Cu-O(2) stretching mode and is correlated with the superconducting transition temperature of the material. No appreciable variation in the center frequency of the Cu-O(2) peak was observed indicating thallium cuprate films are not degraded by our patterning process, even at the edges. Variations in the power handling of Tl-2212 co-planar lines, as determined by measurement of the Third Order Intercept, were not correlated with the Raman results.

Role of Out-of-Plane Copper and Thallium Orbitals in Thallium Cuprate

Simultaneous total and fluorescence yield XAS measurements on Cu L 3 -edge and, for the first time, total yield measurements at TI L 3 -edge of well oriented TI(2212) thin films are reported in this work. Also, Cu L3 and O K-edge measurements on overdoped TI(2212) thin films using bulk sensitive fluorescence yield detection mode are reported showing that large out-of-plane hole densities do exist in the thallium cuprates at least for overdoped samples. Our results suggest that use of a bulk sensitive technique is necessary in order to get a reliable estimation of states having Cu 3d z 2 -r 2 character and thus a precise knowledge of sample stoichiometry. No direct correlation is found between Tc and out-of-plane covalent and doping hole densities such that theones based on the existence of large fraction of these out-of-plane unoccupied states are ruled out. To understand the role of out-of-plane copper orbitals, polarization dependent measurements of Cu L 3 -absorption edge on well characterised TI(2212) thin films have been performed. The density of unoccupied states having 3d z 2 -r 2 character is found to depend on the amount of doping suggesting that out-of-plane copper orbitals essentially play a role of hole reservoir. The energy shift in the positions of white lines of E//(a,b) and E//c spectra is also found to be doping dependent. The probable reason for the observed shift is discussed.

A New Structure Related to the Layered Cuprates: The “1201” Shear-like Phase Tl5Ba3Sr5Cu3O19, Third Member of the Series (TlA2CuO5)m· Tl2A2O4

A thallium cuprate, Tl5Ba3Sr5Cu3O19, whose structure can be derived by systematically shearing the “1201” structure has been synthesized for the first time. It crystallizes in an orthorhombic cell witha=3.7536(2) Å,b=30.631(2) Å,c=9.219(1) Å, andA-type symmetry. This new structure consists of “1201” ribbons parallel to (010) which are three CuO6octahedra wide and are interconnected through “Tl2A2O4” ribbons whose cationic configuration is that of the rock salt structure. This phase can be considered to be them=3 member of a new series with the generic formulation (TlA2CuO5)m·Tl2A2O4withA=Ba, Sr.

Magnetic study of HgBa 2Ca 2Cu 3O 8+ δ single crystals: effect of doping on irreversibility and fishtail lines

Single-crystals of HgBa 2Ca 2Cu 3O 8+ δ (Hg-1223) have been grown and studied by magnetic measurements. By means of successive annealing, T c of the crystals has been varied from 105 K for the as-synthesized crystals to 133 K for the optimized ones. Such a T c variation has allowed the effect of doping on both irreversibility and fishtail lines deduced from half hysteresis loops to be studied. For the Hg-1223 phase the relation between T c and the fishtail line position indicates its underdopeed nature. The comparison of the data for Hg-1223 with that of our single crystals of thallium cuprates shows that the irreversibility line of Hg-1223 stands lower than that of the single Tl-layer cuprates. Moreover the optimized Tl- and Hg-1223 exhibit quite a similar electronic anisotropy in agreement with their similarly layered structure.

Improvement of the Thallium Cuprate Thin Films Due to an Optimization of the Doping Holes Densities as Seen by XAS

Tcoptimization of as-synthesized Tl 2212 thin films can be obtained through post-annealing treatments at low temperatures (180 and 220°C). In this paper, the optimization process was controlled by ac magnetic susceptibility measurements for theTc's and by polarized X-ray absorption spectroscopy measurements for the doping hole densities. The latter technique allows a direct insight into the hole density only in the (a,b) plane of the Tl 2212 structure. All the studied thin films are overdoped with respect to the optimum of 0.12 doping holes per copper defined previously.Tcincreases up to 6 K were observed after post-annealing treatments under an argon atmosphere and were correlated with significant reduction of the doping hole density. In contrast to what has been observed on sintered samples, a post-annealing treatment at 220°C resulted in an insufficient doping hole density, below the optimum, probably resulting from the small sample thickness.

ChemInform Abstract: Electrosynthesis and Electrochemical Behavior of Unusual Solid Thallium‐Based Phases: Thallium Peroxide, Thallium(I)‐Thallium(III) Mixed Oxide, Thallium Cuprate, and Thallium Oxyfluoride.

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Role of out-of-plane copper orbitals in thallium cuprate.

To understand the role of out-of-plane copper orbitals, polarization dependent measurements of Cu ${\mathit{L}}_{3}$-absorption edge on well characterized Tl(2212) thin films have been performed. The density of unoccupied states having 3${\mathit{d}}_{{\mathit{z}}^{2}\mathrm{\ensuremath{-}}{\mathit{r}}^{2}}$ character is found to depend on the amount of doping suggesting that out-of-plane copper orbitals essentially play a role of hole reservoir. The energy shift in the positions of white lines of E\ensuremath{\parallel}(a,b) and E\ensuremath{\parallel}c spectra is also found to be doping dependent. The probable reason for the observed shift is discussed. \textcopyright{} 1996 The American Physical Society.

Mixed Layers in Copper Based Superconducting Materials

Recently discovered series of high Tc superconductors, characterized by the existence of two types of cations within the same layer, are presented. The first family concerns the mercury based cuprates, Hg 1-x M x A 2 Ca m-1 Cu m O 2m+2+δ , with A = Ba and/or Sr, which exhibit structures closely related to that of the thallium cuprates TlBa 2 Ca m-1 Cu m O 2m+3 . They differ from the thallium cuprates by a high oxygen deficiency at the level of the mercury layer. It is shown that cations such as M = Cu, Pb, Tl, Bi, Ce, Pr, Cr, V, Mo, W, Ti, Sr, Ca,... can partially substitute for mercury ions, stabilizing the structures. The cationic composition of the layer depends indeed on the nature of the M cation but also on that of the alkaline earth A. For given A and M cations, the x value remains unchanged even when the number of copper layers varies. M and Hg cations are either statistically distributed over the same site or ordered. Different types of ordering have been detected. Another way of generating mixed layers is to shear periodically the structure, leading to the formation of the so called collapsed phase. In the collapsed bismuth cuprates, bismuth and copper segments, a few octahedra long, alternate in strongly waving layers. In the collapsed oxycarbonates, carbonate groups and M cations are ordered within the intermediate layer so that they can be simply described from a partial and ordered substitution of carbon for Hg, Tl, Bi and other M cations building the intermediate layer. The oxycarbonitrates (Y 1-x Ca x ) n Ba 2n Cu 3n-1 (C,N)O 3 O 7n-3 can also be described as an ordered substitution of carbon for copper in the 123 matrix. The different families of superconducting materials which are generated by such mechanisms are described as well as the way the different species are distributed within the mixed layers. Their influence on the physical properties are discussed.

Electrosynthesis and electrochemical behaviour of unusual solid thallium-based phases: thallium peroxide, thallium(I)-thallium(III) mixed oxide, thallium cuprate, and thallium oxyfluoride

Possibilities are demonstrated of varying the modes and conditions of anodic electrocrystallization in order to modify the mechanism of this process and to obtain, together with Tl 2O 3, other oxide phases on different substrates from Tl + solutions. Using the methods of voltammetry, chronopotentiometry, gravimetry, Auger spectroscopy, and X-ray diffractometry, individual phases of thallium peroxide, a mixed-valence oxide, cuprate, and oxyfluoride synthesized by this process were characterized. For the first time, the boundaries of the thermodynamic stability regions were estimated for poorly studied thallium oxide phases in aqueous solutions.

The Superconducting Copper Oxychromate Tl3(CrO4)Sr8Cu4O16: Long-Range Ordering between Thallium and Chromium

Long-range ordering between chromium and thallium has been evidenced for the first time in the copper oxychromate Tl3(CrO4)Sr8Cu4O16 using HREM and XRD. This compound, which crystallizes in an orthorhombic cell with a = 3.778 (1) A, b = 15.244 (1) A, and c = 17.677 (1) A, derives from the “1201” TlSr2CuO5 structure, by replacing one row of Tl atoms out of four by one row of chromate groups in an ordered way. This superconductor, whose Tc(onset) can be raised to 34 K after argon−hydrogen annealing, exhibits a rather high superconducting volume fraction (>40%) compared to other “1201” thallium cuprates. Doping with lanthanum destroys the long-range ordering and weakens superconductivity. The electron microscopy study of this phase also shows the existence of other local superstructures that are interpreted in terms of various modes of ordering of Tl atoms and CrO4 groups.