Electron paramagnetic resonance obtained from the tetragonal RBa2Cu3O6+x (R=Nd, Sm, Tm) compounds exhibit a well defined line resulting from coupled divalent Cu ions. Below 20 K the g parameter of this signal is strongly temperature dependent. At about the same temperatures there is a ferromagnetic-like transition in the magnetic susceptibility.

EPR, XRD, and magnetic studies are presented for Pro.sReo.sBa2Cu307-a compounds (Re = La, Nd, Sin, Eu, Gd, Dy, Ho, Y, Er, Tm, Yb, and Lu) in the orthorhombic and tetragonal (large oxygen deficiency) phase. For the samples with Re = Dy, Ho, Y, Er, Tin, Yb, and Lu in the orthorhombic phase, the transition to the superconducting state has been observed in the temperatures range T~ between 18 and 40 K. For the samples with Nd and Yb in the tetragonal phase, EPR spectra coming from trivalent rare earth ions have been recorded. In the nonoxygenated sample Pro.sLao.sBa2Cu307-a the EPR spectrum arising from the nonKramers trivalent praseodymium ion has been observed. A broad EPR line appearing in all our samples was attributed to superexchange interaction between copper ions over oxygen (O~) bridges. Interestingly, for the Pro sReo.sBa2Cu307-6 (Re = Er and Lu) compounds in the tetragonal phase at liquid-nitrogen temperature, a nonresonant microwave absorption in low magnetic fields has been detected.

The crystal and magnetic structures of the perovskite YBaCuFeO5+delta have been studied in the temperature range T = 4.2-300 K by powder neutron diffraction. In addition to the antiferromagnetic ordering transition at T-N = 442 K, a commensurate-incommensurate magnetic transition is detected at T'(N) = 190 K. Below this temperature, two sets of satellite peaks surround the (1/2, 1/2, 1/2) magnetic peak at d similar to 5.15 Angstrom, collapsing into a single set of satellites below 155 K. Polarization analysis has been performed to confirm the magnetic nature of the (1/2, 1/2, 1/2)(+/-) satellites.

The structure and the physical properties of the oxygenated and deoxygenated compounds of the series SmBa2−xSrxCu3O6+y (x = 0.0, 0.25, 0.5, 0.75, 1.0 and 1.25) are studied. In the XRD spectra of the oxygenated compounds a structure of tetragonal symmetry is revealed beyond the value of x = 0.75 and the upper limit for substitution of Sr for Ba is x = 1.0. Resistivity and magnetization measurements of the fully oxygenated compounds show that the Tc values decrease with increasing Sr content and this is discussed in relation to the observed structural changes deduced by the Rietveld analysis of the XRD spectra. The bond length changes that occur in the coordination sphere of Cu(1), Cu(2) and (Ba,Sr) atoms are consistent with the “charge redistribution” model, i.e., electrons are transferred from Cu(2) to Cu(1) atoms and the number of holes on the “Cu(2) superconducting planes” increases beyond the optimum value inducing a reduction in the Tc. The Raman measurements support the charge redistribution and the stress relaxation models as probable explanations for the reduction of Tc upon Sr substitution.

RBa2Cu3O7 and [R0.5Pr0.5]Ba2Cu3O7 compounds with RY and lanthanides have been prepared and studied at ambient temperature by means of XRD and infrared-reflectance spectroscopy. In Pr free compounds, increasing the Shannon radius of R, rR, leaves the puckering of the Cu(2)−O(2, 3) sheet unaffected. In the Pr containing compounds, the PrO coordination polyhedron is typical of R+3 ions in eight-fold coordination and argues against differentiating Pr in terms of valence or hybridization. Instead, a repositioning of Ba within the cuprate block is observed, leading to the flattening of the sheet and the anomalously high frequency of the Ba and Cu(2)−O(2, 3) B1u modes. In RPr compounds the c-axis and the interplanar distances related to the position of Ba and O(2, 3) are found to exhibit a sigmoidal dependence on rR. It is argued that this sigmoidal dependence is related to the two-mode behavior exhibited by several phonon modes of these compounds.

XRD, magnetic susceptibility, and EPR studies are reported for the BaCuO2+x compound in both the oxygenated and nonoxygenated phases. The XRD analysis has shown essential differences in the disordered part between the oxygenated and the nonoxygenated samples. The magnetic susceptibility measurements have shown strong ferromagnetic intracluster interactions among copper ions in the ordered part of the compound. At low temperature, antiferromagnetic intercluster interactions mediated by the disordered part predominate. EPR measurements in both phases have revealed a spectrum of Cu2+ ions, in orthorhombic local symmetry, which is attributed to copper ions in the disordered part. An intense exchange-narrowed EPR line has also been observed in both phases, which is ascribed to the copper clusters in the ordered part. The temperature dependence of the intensity and linewidth of this line is consistent with the bulk magnetic behaviour. At low temperature, the divergent behaviour of the EPR parameters indicates that antiferromagnetic ordering may occur. Additionally, it was found that the EPR spectra are essentially influenced by thermal treatment and the ordering of the oxygen atoms in the disordered part of the compound.

The crystal structure, the magnetic and transport properties, and the lattice vibrations of the (Y,Ce${)}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CuFeO}}_{8}$ compound were studied by Rietveld refinement, M\"ossbauer spectroscopy, dc magnetic susceptibility, electrical-resistivity measurements, and Raman spectroscopy. The Rietveld-refinement results and Raman spectra show that the space group which describes the structure is P4mm. M\"ossbauer spectra can be fitted with one component with hyperfine parameters which correspond to ${\mathrm{Fe}}^{+3}$ in a high-spin state coordinated by five oxygen atoms arranged in a square pyramid. Most of the observed phonon lines can be assigned to definite atomic vibrations. Magnetic measurements show an antiferromagnetic transition at 30 K. Fitting of dc-susceptibility data in the paramagnetic region gives an effective magnetic moment of (3.6\ifmmode\pm\else\textpm\fi{}0.1)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ per ion. The resistivity data show insulating behavior.

We present results of a micro-Raman study of well characterized by X-rays powder diffraction (XPD) and a.c. magnetic susceptibility samples of YBa2(Cu1−xFex)4O8 (0≤×≤0.06). Employing that Cu at both the Cu1 and Cu2 sites is involved in Raman active modes, we show that Fe substitutes for Cu at the Cu1 site. Although the XPD data analysis reveals orthorombic-to-tetragonal transition for x≥0.04, a Raman scattering evidence is given that the material remains orthorhombic at micro-level even for high x.

The magnetic and crystal structures of the oxygen-deficient layered perovskite YBaCuFeO5+DELTA have been determined with powder neutron diffraction methods. It crystallizes in the noncentrosymmetric tetragonal space group P4mm with a = 3.8707(2) angstrom and c = 7.6711(4) angstrom (at room temperature). Structural motifs of corner-sharing severely elongated CuO5 (Cu-O(eq) = 1.936(2) angstrom, Cu-O(ax) = 2.35(9) angstrom) and slightly squashed FeO5 (Fe-O(eq) = 2.03(3) angstrom, Fe-O(ax) = 1.82(9) angstrom) square pyramids result in a novel lamellar structure with ordered oxygen defects. Local magnetic moments directed perpendicular to the unique axis (mu perpendicular to c, mu = 2.51(15) mu(B) at room temperature) appear at the Fe3+ sites at 442.4(5) K. The magnetic unit cell results by doubling the chemical one along all three crystallographic directions (magnetic propagation vector, k = (1/2,1/2,1/2)). Despite the long separation between successive FeO2 layers (approximately 7.7 angstrom), the magnetic behavior can be successfully described by a three-dimensional Heisenberg spin Hamiltonian with a critical exponent beta = 0.366(8). No evidence of ordering of the Cu sublattice is found on cooling to room temperature.

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The polarized Raman scattering of the R0.5Pr0.5Ba2Cu3O7-delta series (R = La, Pr, Nd, Sm, Eu, Gd, Dy, Y, Ho, Er, Tm, Yb, Lu; delta approximately 0) which undergoes a superconductor-to-nonsuperconductor transition between R = Gd and Dy was studied. It was found that the appearance of superconductivity correlates with observation of a two-mode behavior of the R-ion-size-sensitive B1g-like mode of 0(2),O(3) out-of-phase vibrations. It was also established that the Ba (xx,A(g)) phonon line is of asymmetrical (Fano) shape for all R. The origin of the Fano effect usually attributed to interference with an electronic continuum is discussed.

The polarized Raman scattering of the ${\mathit{R}}_{0.5}$${\mathrm{Pr}}_{0.5}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ series (R=La, Pr, Nd, Sm, Eu, Gd, Dy, Y, Ho, Er, Tm, Yb, Lu; \ensuremath{\delta}\ensuremath{\sim}0) which undergoes a superconductor-to-nonsuperconductor transition between R=Gd and Dy was studied. It was found that the appearance of superconductivity correlates with observation of a two-mode behavior of the R-ion-size-sensitive ${\mathit{B}}_{1\mathit{g}}$-like mode of O(2),O(3) out-of-phase vibrations. It was also established that the Ba (xx,${\mathit{A}}_{\mathit{g}}$) phonon line is of asymmetrical (Fano) shape for all R. The origin of the Fano effect usually attributed to interference with an electronic continuum is discussed.

The EPR spectra of the members of the series Pr0.5RE0.5Ba2Cu3O6+x (RE = Pr, La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, Yb, and Lu) in the orthorhombic phase are investigated at low temperature. The EPR spectra arise from two different paramagnetic centers, one from divalent copper ions in orthorhombic local crystal field symmetry and another from exchange coupled pairs of copper ions whose origin is discussed. The EPR spectra essentially depend on the time exposition. The EPR spectra of some divalent and trivalent rare earth ions are recorded. The crystal field analysis is done for the trivalent ytterbium ions. The semiconducting behaviour of the dc conductivity can be attributed to thermally activated small polaron hopping motion.

The structure and physical properties of the NdBa2-xSrxCu3O7 system has been studied in relation to the strontium content x. The orthorhombic structure transforms to tetragonal beyond x = 0.6, single phase samples are produced in the range of x = 0.0 to 1.0 and all the studied samples are superconductors.

physica status solidi (b)Volume 182, Issue 1 p. K19-K23 Short Note High-Tc Superconductor LuBa2Cu3O6 + x N. Guskos, N. Guskos Section of Solid State Physics, Department of Physics, University of Athens Search for more papers by this authorV. Likodimos, V. Likodimos Section of Solid State Physics, Department of Physics, University of Athens Search for more papers by this authorA. Koufoudakis, A. Koufoudakis Institute of Materials Science, National Research Center Democritos, Athens Search for more papers by this authorC. Mitros, C. Mitros Institute of Materials Science, National Research Center Democritos, Athens Search for more papers by this authorH. Gamari-Seale, H. Gamari-Seale Institute of Materials Science, National Research Center Democritos, Athens Search for more papers by this authorM. Wabia, M. Wabia Institute of Physics, Technical University of Szczecin Search for more papers by this author N. Guskos, N. Guskos Section of Solid State Physics, Department of Physics, University of Athens Search for more papers by this authorV. Likodimos, V. Likodimos Section of Solid State Physics, Department of Physics, University of Athens Search for more papers by this authorA. Koufoudakis, A. Koufoudakis Institute of Materials Science, National Research Center Democritos, Athens Search for more papers by this authorC. Mitros, C. Mitros Institute of Materials Science, National Research Center Democritos, Athens Search for more papers by this authorH. Gamari-Seale, H. Gamari-Seale Institute of Materials Science, National Research Center Democritos, Athens Search for more papers by this authorM. Wabia, M. Wabia Institute of Physics, Technical University of Szczecin Search for more papers by this author First published: 1 March 1994 https://doi.org/10.1002/pssb.2221820130Citations: 1 Panepistimiopolis, GR-15784 Zografos, Athens, Greece. Aghia Paraskevi, Attikis, GR-15310 Athens, Greece. Al. Piastow 17, PL-70-310 Szczecin, Poland. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume182, Issue11 March 1994Pages K19-K23 RelatedInformation

Raman and XRD study of the effects of Sr substitution for Ba in the series SmBa2−xSrxCu3Oy is reported for x=0.0 up to 1.25. The profound changes in the interatomic distances, given by XRD, as well as the trends of the Raman spectra, are indicative of the carrier redistribution and tension release, induced by the Sr substitution, after the phase transition to the tetragonal structure at Sr concentrations of x=0.75.

The crystal structure, the magnetic and transport properties, and the lattice vibrations of the (Y,Ce)2Sr2CuFeO8 compound were studied by Rietveld refinement, Mossbauer spectroscopy, dc magnetic susceptibility, electrical-resistivity measurements, and Raman spectroscopy. The Rietveld-refinement results and Raman spectra show that the space group which describes the structure is P4mm. Mossbauer spectra can be fitted with one component with hyperfine parameters which correspond to Fe+3 in a high-spin state coordinated by five oxygen atoms arranged in a square pyramid. Most of the observed phonon lines can be assigned to definite atomic vibrations. Magnetic measurements show an antiferromagnetic transition at 30 K. Fitting of dc-susceptibility data in the paramagnetic region gives an effective magnetic moment of (3.6 +/- 0.1)mu(B) per ion. The resistivity data show insulating behavior.

physica status solidi (b)Volume 181, Issue 2 p. K69-K72 Short Note EPR Spectra of Polycrystalline REBaCuFeO5 (RE = Eu, Y, Yb) N. Guskos, N. Guskos Department of Physics, Institute of Solid State Physics, University of Athens Search for more papers by this authorV. Likodimos, V. Likodimos Department of Physics, Institute of Solid State Physics, University of Athens Search for more papers by this authorJ. Kuriata, J. Kuriata Institute of Physics, Technical University of Szczecin Search for more papers by this authorH. Metz, H. Metz Fachbereich Physik der Universität Leipzig Search for more papers by this authorW. Windsch, W. Windsch Fachbereich Physik der Universität Leipzig Search for more papers by this authorM. Wabia, M. Wabia Institute of Physics, Technical University of Szczecin Search for more papers by this authorC. Mitros, C. Mitros Institute of Material Science, N.C.S.R. “Democritos”, Athens Search for more papers by this authorD. Niarchos, D. Niarchos Institute of Material Science, N.C.S.R. “Democritos”, Athens Search for more papers by this author N. Guskos, N. Guskos Department of Physics, Institute of Solid State Physics, University of Athens Search for more papers by this authorV. Likodimos, V. Likodimos Department of Physics, Institute of Solid State Physics, University of Athens Search for more papers by this authorJ. Kuriata, J. Kuriata Institute of Physics, Technical University of Szczecin Search for more papers by this authorH. Metz, H. Metz Fachbereich Physik der Universität Leipzig Search for more papers by this authorW. Windsch, W. Windsch Fachbereich Physik der Universität Leipzig Search for more papers by this authorM. Wabia, M. Wabia Institute of Physics, Technical University of Szczecin Search for more papers by this authorC. Mitros, C. Mitros Institute of Material Science, N.C.S.R. “Democritos”, Athens Search for more papers by this authorD. Niarchos, D. Niarchos Institute of Material Science, N.C.S.R. “Democritos”, Athens Search for more papers by this author First published: 1 February 1994 https://doi.org/10.1002/pssb.2221810233Citations: 5 Panepistimiopolis, GR-15784 Zografos, Athens, Greece. Al. Piastow 17, PL-70-310 Szczecin, Poland. Linnéstr. 5, D-04103 Leipzig, Federal Republic of Germany. Aghia Paraskevi, GR-15310 Attikis, Athens, Greece. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat References 1 M. Pissas, C. Mitros, V. Psycharis, G. Kalias, A. Simopoulos, A. Kostikas, D. Niarchos, C. Xristiadis, and K. Prassidis, Proc. VII Hellenic Solid State Physics Conf., 20 to 22 Sept. 1991, Thessaloniki (Greece) (p. 424). Google Scholar 2 L. Er-Rakho, C. Miceli, P. Lacorve, and B. Ravean, J. Solid State Chem. 73, 531 (1988). 10.1016/0022-4596(88)90141-7 CASWeb of Science®Google Scholar 3 C. M. Brodbeck, J. non-crystall. Solids 40, 305 (1980). 10.1016/0022-3093(80)90108-8 CASWeb of Science®Google Scholar 4 D. J. Newman and W. J. Urban, J. Phys. C 5, 3101 (1972). 10.1088/0022-3719/5/21/015 CASWeb of Science®Google Scholar 5 A. Abraham and B. Bleaney, Electron Paramagnetic Resonance of Transition Ions, Clarendon Press, Oxford 1970. Google Scholar Citing Literature Volume181, Issue21 February 1994Pages K69-K72 ReferencesRelatedInformation