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Oxygen nonstoichiometry, structural phase transitions and anomalous Pr ordering for PrBa2-xLaxCu3Oz solid solution

H M Luo1,5, S Y Ding1, G X Lu1, B N Lin2, H C Ku2, C H Lin3, H-C I Kao3 and J C Ho4

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The oxygen nonstoichiometry, structure, magnetic and calorimetric data for La doped Ba-site PrBa2-xLaxCu3Oz systems (0≤x≤1 and 6.881≤z≤ 7392) are reported. The x-dependence of the oxygen content increases monotonically and two structural phase transitions are observed, confirmed by powder x-ray Rietveld analysis, from the orthorhombic 1212C-phase (space group: Pmmm) to tetragonal 1212 (P4/mmm) at x = 0.45, and then to another orthorhombic (Cmmm) phase around x = 0.7. Magnetic susceptibility and heat capacity measurements show that the anomalous Néel temperature TN(Pr) decreases monotonically from 18 K for x = 0 to 2.8 K for PrBa1.3La0.7Cu3O7.236 and to below 2 K for x≥0.8 for samples prepared under the same conditions, while TN(Pr) increases with an increase of oxygen content for the same compound. The increasing Pr-O bond length observed with decreasing TN(Pr) indicates that this unusual Pr magnetic ordering is closely related to the wave-function overlap between the Pr-4f orbital and eight O-2pπ orbital in the CuO2 bi-layer. No superconductivity has been detected for these insulating cuprates.


PACS

74.72.Dn La-based cuprates

61.05.cp X-ray diffraction

74.25.Dw Superconductivity phase diagrams

74.25.Bt Thermodynamic properties

74.25.Ha Magnetic properties

64.70.K- Solid–solid transitions

Subjects

Superconductivity

Condensed matter: structural, mechanical & thermal

Dates

Issue 6 (June 2001)

Received 4 December 2000, in final form 20 December 2000



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