Thermochemical study of Ln2O3, T′-Ln2CuO4, and Ln2Cu2O5 (Ln = Rare Earth)

E. Takayama-Muromachi, A. Navrotsky

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High temperature solution calorimetry using a 2PbO · B2O3 solvent at 977 K was applied to the high Tc -related compounds, Ln2O3 (Ln = Nd-Lu), T′-Ln2CuO4 (Ln = Nd-Gd), and Ln2Cu2O5 (Ln = Dy-Lu). The heat of solution, ΔHs, of Ln2 O3 becomes less exothermic with decreasing size of Ln3+ from ∼ -130 kJ/mole in La2O3 to ∼ -30 kJ/mole in Lu2O3. The heats of solution of rare earth oxides containing unevenly filled “4f” orbitals are slightly more endothermic than those predicted by a straight line relating ΔHs to reciprocal ionic radius, 1/r, for La, Gd, Y, and Lu, presumably reflecting the crystal field stabilization energy of Ln3+ (CFSE) in the solid. The heat of solution of the T′ phase when plotted against 1/r shows a maximum value at Ln = Sm. This may be explained by the CFSE and/or by a nonlinear change in lattice energy of the T′ phase as a function of 1/r. The stability relations between T′ and Ln2Cu2O5 structures are discussed using the thermochemical data obtained. The data generally confirm patterns of stability seen in synthesis experiments.

Original languageEnglish (US)
Pages (from-to)349-356
Number of pages8
JournalJournal of Solid State Chemistry
Issue number2
StatePublished - Oct 1993
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry


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