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Employing oxide-melt drop-solution calorimetry, we have performed the first comparative thermochemical investigations of the title compounds. The enthalpies of formation of the Ln123 derivatives display an essentially linear trend toward less exothermic values with increasing lanthanide atomic number, implying that these phases become more stable with increasing lanthanide radius. In contrast, the enthalpies of oxidation vary to only a minor extent with the choice of lanthanide and suggest that the chain-site charge distributions of the Ln123 are comparable. The thermodynamic characteristics of Pr123 generally follow the trends established by the other Ln123 and reveal no gross energetic anomaly associated with the suppression of superconductivity. The enthalpies of formation of the Ln124 derivatives manifest a maximum at Gd124, while the unit-cell volumes and enthalpies of drop-solution and formation of these compounds are nearly constant multiples (2.3, 1.6−1.7, and 1.3−1.4, respectively) of the corresp...

The enthalpies of formation and the partial molar enthalpies of oxidation of polycrystalline LnBa2Cu3Oy (Ln = Pr, Nd, Eu, Gd, Dy, Ho, Tm) and Y1−xPrxBa2Cu3Oy (x = 0.0, 0.1, 0.2, 0.5, 0.8, 0.9, 1.0) have been determined at 298 K by drop-solution calorimetry. The thermodynamic characteristics of Pr123 follow the trends of the trivalent-ion-based Ln123 compounds. The thermodynamic data for the (Y,Pr)123 solid solutions show nonideal solution behavior, but no x-dependent valence instability. The superconducting critical temperatures and the enthalpies of oxidation of the (Y,Pr)123 solid solutions are linearly related.