Determination of the valence of Pr, Gd, and Ho inYBa2Cu3

Comparative study on structure and magnetic properties of polycrystalline PrxY1−xBa2Cu3O7−δ prepared in oxygen and argon atmosphere

“…At the same time, it was argued that a change in Pr-O distance might cause a change of Pr valence (and several measurements [14,15] seem to confirm such a change). Even though some X-ray spectroscopy and photoemission measurements [16,17] suggest that Pr occurs only in the trivalent state in these materials, others [18][19][20] strongly suggest a possibility of variable Pr valence. In the last two decades, superconductivity in Pr-123 samples has been reported by some authors where the method of syntheses appears to be responsible for the formation of the stable superconducting phase [21][22][23].…”

Enhancement of critical Pr ion concentration (xcr) in (La1−xPrx)Ba2Cu3Oz

“…For example, magnetic 5 and chemical substitution 6,7 studies point to the tetravalent state while x-ray photoelectron spectroscopy ͑XPS͒ 8 and x-ray absorption near-edge spectroscopy 9 ͑XANES͒ investigations suggest the trivalent state. On the contrary, neutron diffraction 10 and x-ray absorption studies 11 have revealed a mixed valence state. Even though the spectroscopic ͑XPS͒ results for pure and substituted Pr-1:2:3 indicate a trivalent state, it is, however, difficult to assess the true value of Pr from the XPS core levels, i.e., the Pr (3d 5/2 ) overlaps directly with the Cu (2p 3/2 ) level and hence the dilemma.…”

“…4 Several mechanisms have been proposed to account for the systematic suppression of superconductivity in (RE 1Ϫx Pr x )Ba 2 Cu 3 O z by Pr ion and most of them centered on the valence state of Pr, which is under controversy. [5][6][7][8][9][10][11] Ionic size of the rare earth element is also crucial as it leads to steric effects, resulting in distortion of the local environment around the rare earth ion. 12 These localized effects may play a very significant role: if the perturbations extend to the adjacent layers where the superconducting electrons are confined this can cause some changes in the bond lengths of the Cu-O layers, which strongly affect the superconductivity in high-T c cuprates.…”

PrBa2Cu3O7−y investigated by141Pr Mössbauer spectroscopy

“…Because the first three properties resemble that of the oxygen depleted phase REBa2Cu306, the suppression of the superconducting state in PrBa2Cu307_y was originally attributed to the filling of the superconducting holes due to a tetravalent or mixed valency of Pr [2]. However, later studies excluded the presence of any Pr 4 § in PrBa2Cu307_y [3]. In these studies, the hybridization of the Pr-4f levels with the Cu-O plane bands was instead postulated as a cause for the suppression of the superconducting state, but questions remained because some of these studies did show some features that could not be explained on the basis of solely trivalent Pr [3].…”

“…However, later studies excluded the presence of any Pr 4 § in PrBa2Cu307_y [3]. In these studies, the hybridization of the Pr-4f levels with the Cu-O plane bands was instead postulated as a cause for the suppression of the superconducting state, but questions remained because some of these studies did show some features that could not be explained on the basis of solely trivalent Pr [3]. Furthermore, other studies, such as neutron diffraction, did indicate an intermediate valent Pr [4].…”