The high pressure synthesis and characterization of some rare-earth based praseodymium-substitute R2Ba4Cu7O14+δ (R = Sm, Gd, Ho) caprates
01 Aug 1997-Physica C-superconductivity and Its Applications (North-Holland)-Vol. 281, Iss: 2, pp 198-204
TL;DR: In this paper, the stability of Pr-doped R247 phases with substitution limit (x ) equal to 0.0 and with an increment of 0.1 in x was investigated.
Abstract: The stability of phases in the (R 1 − x Pr x ) 2 Ba 4 Cu 7 O 14 + δ (R = Sm, Gd, Ho; Pr-doped R247) systems with x = 0 to 1.0 and with an increment of 0.1 in x was investigated. Samples of the title Pr-doped R247 phases were prepared at 980–990°C under 20–36 bar of oxygen atmosphere, followed by long-time annealing at 300–320°C under 110–115 bar of oxygen. Single-phased samples were obtained with substitution limit ( x ) equal to 0.5, 0.6 and 0.7 for phases of the title (R 1 − x Pr x ) 2 Ba 4 Cu 7 O 14 + δ series with R = Sm, Dg, and Ho, respectively, as indicated by X-ray increasing Pr cement ( x ) both the lattie parameters and unit-cell volume were found to increase monotonically and, however, the corresponding crystallographic orthorhombicity, 2( b − a )/( b + a ), was found to decrease with increasing x for all three Pr-doped series. The T c of the Pr-doped R247 phases where found to suppressed from 69, 70 and 92 K down to 20 K ( x = 0.4), 18 K ( x = 0.5) and 8 K ( x = 0.7) for Pr-doped R247 phases with R = Rm, Gd, and Ho, respectively. The composition coefficients of T c , d T c /d x ,were found to be −50.4, −48.5, and −55.5 K./Pr-atom per formula unit for the title Pr-doped R247 series with R = Sm, Gd, Ho, respectively. The crystal structure, temperature-dependent resistivity and magnetization data of the Pr-doped R247 phases synthesized in our study are described and their implications are discussed.
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TL;DR: In this paper, the authors present the results of a study of the structure and transport properties of the series of compounds Y1−xPrxBa2Cu3O7−δ (x = 0−1.0), in which they observe a monotonic decrease in Tc and eventually a metal-nsulator transition with increasing Pr concentration.
Abstract: Considerable excitement has been generated by the report of superconductivity above 90 K in a multi-phase Y–Ba–Cu oxide1. The superconducting phase was subsequently identified as YBa2Cu3O7−δ2,3. The complete replacement of Y by the trivalent rare-earths La–Lu, with the exception of Ce, Pr and Tb, yields a superconducting phase with a critical temperature (Tc) almost identical to that reported for the yttrium compound4–7. This is somewhat surprising as most of these ions carry significant magnetic moments, the presence of which rapidly decreases Tc in ordinary superconductors. The three exceptions noted, Ce, Pr and Tb, are the rare-earth ions which have a stable tetravalent state. Here we present the results of a study of the structure and transport properties of the series of compounds Y1−xPrxBa2Cu3O7−δ (x = 0−1.0), in which we observe a monotonic decrease in Tc and eventually a metal–nsulator transition with increasing Pr concentration. To date, this is the only rare-earth ion which has been found substantially to alter Tc upon partial substitution for Y.
406 citations
TL;DR: In this article, a new superconducting phase has been identified during measurements of the pressure-temperature-composition phase diagram of the pseudobinary system YBa2Cu3O6+x−O2.
Abstract: A new superconducting phase has been identified during measurements of the pressure–temperature–composition phase diagram of the pseudobinary system YBa2Cu3O6+x–O2 (ref. 1). The new phase has formula unit Y2Ba4Cu7O14+x. Preliminary crystallographic results from electron diffraction showed a doubling of the c-axis1. Here we report the results of a single-crystal X-ray structural study and measurements of superconductivity in the new compound. The superconducting onset, from a.c. susceptibility measurements, is ˜40 K. The structure (space group Ammm) consists of single YBa2Cu3O6+x -type blocks containing single corner-sharing CuO4 square-planar chains, alternating with single YBa2Cu4O8-type blocks containing double edge-sharing CuO4 square-planar chains. This suggests the possibility of similar compounds with other ordered sequences of single and double chains.
271 citations
TL;DR: The superconductivity is strongly suppressed as a function of Pr concentration, with a behavior which is consistent with the classical Abrikosov-Gor'kov pair-breaking theory, and the critical fields versus {ital T} show a bell''-shaped behavior, which is inconsistent with the presence of magnetic pair- Breaking interactions.
Abstract: Substitution of Pr for Y in the Y{sub 1{minus}{ital x}}Pr{sub {ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} system depresses {ital T}{sub {ital c}}, with superconductivity disappearing for {ital x}{ge}0.5. The origin of this {ital T}{sub {ital c}} depression is still controversial, as is the valence state of the Pr ion. In order to study these problems, single-phase materials were prepared with {ital x}=0.0, 0.1, 0.2, 0.3, 0.35, 0.4 0.45, 0.5, 0.6, 0.7, 0.9, and 1.0. Under certain annealing conditions, these types of samples will phase separate into YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} and Y{sub 1{minus}{ital x}}Pr{sub {ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, showing two transitions in the magnetization, but will still appear single phase from x-ray diffraction. We have overcome this problem through specific annealing conditions of time, temperature, and atmosphere. We find that the superconductivity is strongly suppressed as a function of Pr concentration, with a behavior which is consistent with the classical Abrikosov-Gor'kov pair-breaking theory. The critical fields versus {ital T} show a bell''-shaped behavior, which is consistent with the presence of magnetic pair-breaking interactions. The measured temperature dependence of the critical field, {ital H}{sub {ital c}2} near {ital T}{sub {ital c}}, and the Pauli susceptibility, are used to estimate the physicalmore » parameters {lambda}{sub GL}, {xi}{sub GL}, and {gamma}.« less
235 citations
TL;DR: Electron-energy-loss spectroscopy suggests that Pr localizes mobile holes thereby leading to the suppression of superconductivity and the metal-insulator transition.
Abstract: Electron-energy-loss spectroscopy has been used to investigate the changes of the electronic structure in ${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ (0\ensuremath{\le}x\ensuremath{\le}1). The O 1s absorption edges and the low-energy-loss function indicate that Pr does not fill holes in the ${\mathrm{CuO}}_{2}$ planes. This suggests, by comparison with other experiments, that Pr localizes mobile holes thereby leading to the suppression of superconductivity and the metal-insulator transition.
198 citations
TL;DR: In this paper, a modification of the idometric method that is particularly suited to analyses of La/sub 2-x/Sr/sub x/CuO/sub y/ and YBa/sub 1.
Abstract: Studies of the composition of YBa/sub 2/Cu/sub 3/O/sub y/ in which the oxidation states of Y and Ba are +3 and +2, respectively, have shown a direct relationship between the Cu(II)/Cu(III) ratio and the oxygen stoichiometry. Idometry or hydrogen reduction has generally been used for the Cu(III) determination. A modification of the idometric method that is simple to apply and is particularly suited to analyses of La/sub 2-x/Sr/sub x/CuO/sub y/ and YBa/sub 2/Cu/sub 3/O/sub y/ is described. The results of application to determination of the oxygen content of YBa/sub 2/Cu/sub 3/O/sub y/ are presented, and the oxygen content is related to the crystallographic and superconducting properties of the material. Results indicated that at room-temperature large variations of the oxygen content of the orthorhombic phase of YBa/sub 2/Cu/sub 3/O/sub y/ could occur without change in the lattice parameters or appreciable impairment of the resistive superconducting transition or diamagnetic properties. 13 references, 1 figure, 1 table.
173 citations