Electronic properties ofBa2Y1−xPr

Abstract

Measurement of the Hall coe%cient in the Ba2Yl -Pr"Cu307-& system has revealed that an increase in Pr concentration reduces the Hall carrier number (1/eRH) and its strong temperature dependence. The Cu formal valence calculated from the Pr valence, which has been determined to be -+3. 5, shows a weakly decreasing dependence on Pr concentration. T, shows a stronger dependence on the Hall carrier number and the Cu-0 formal valence than in the oxygen-depleted Ba2YCu307-g system. The persistence of the chain band explains this observed difference, suggesting that the actual Cu-0 valence dependence of the 90-K superconductor is stronger than that of the 40-K superconductor.Of known Ba2[lanthanide]Cu307s compounds, only the Pr compound shows neither superconductivity nor metallic conduction, although it has an orthorhombic structure isomorphic to that of Ba2YCu307 (Refs. 1 and 2). Thus, the difference in the electronic and/or the crystal structure between these compounds might be a key parameter controlling superconductivity as well as normalstate properties of the high-T, copper oxides. It is known that a series of single-phase Ba2Y1-"Pr"Cu307-s can be synthesized. 34 They continuously range from superconductors to insulators. It is generally accepted that in high-T, copper oxides, the total carrier density is a crucial parameter by which the conduction properties are determined.There are several systems, for example,

X-ray absorption spectroscopy of detwinnedPrxY1−

“…Even with this reduction, there are still 0.44 holes located on the chain unit of Pr 0. 8 37 is inconsistent with the findings of the neutron diffraction measurements, as mentioned above. By and large, it may be said that the LM approach would, in principle, agree with our NEXAFS data if the FR band exhibited greater p z character above E F than expected from Fig.…”

“…Therefore, we assume that the feature at 529.5 eV in the Eʈa spectrum of Pr 0. 8 ) for polarization Eʈa has to be scaled by a factor of 2 in order to take all planar contributions into account. The scaled difference spectrum is shown in Fig.…”

“…Among those rare-earth-based cuprates that are isostructural to YBa 2 Cu 3 O 7Ϫy , the PrBa 2 Cu 3 O 7Ϫy compound is a puzzling exception since it shows neither metallic nor superconducting behavior. [6][7][8][9][10] Upon substituting Pr into the Pr x Y 1Ϫx Ba 2 Cu 3 O 7Ϫy system, T c decreases [11][12][13] and, in the case of yϷ0.1, finally vanishes for Pr fractions x beyond 0.55. This transition seems to be accompanied by a change from metallic to semiconducting characteristics.…”

“…This approach implies that the suppression of superconductivity results from a reduced number of charge carriers in the CuO 2 planes. Magnetic susceptibility, 6,8,12 Hall effect, 8 thermopower, 7,9,10 nuclear magnetic resonance, 15 muon-spin relaxation, 16 and neutron diffraction measurements [22][23][24] have been interpreted in terms of hole depletion. On closer inspection, however, it has been shown that these results can also be understood as an indication for Pr 3ϩ .…”

Magnetic and superconducting properties of Pr in La1−xPrxBaCaCu3O7 system with 0.0⩽x⩽1.0

“…This compound crystallizes in ideal orthorhombic RE:123 structure, similar to that of other superconducting compounds of this family, yet with no superconductivity. [4][5][6][7][8][9][10][11][12][13][14][15] In fact, PrBa 2 Cu 3 O 7 is an antiferromagnetic insulator, with Cu spins in CuO 2 planes ordered near room temperature and Pr moments ordered at nearly 17 K. 15 However, as far as we know, three reports exist in literature which claim superconductivity of Pr:123: one on laser ablated Pr 0. 5 There are several models in the literature which try to explain the nonobservation of superconductivity in PrBa 2 Cu 3 O 7 .…”