Ghamaty, S., B. W. Lee, J. J. Neumeier, G. Nieva, and M. B. Maple. "Lowtemperature specific heat of the Y1xPrxBa2Cu3O7δ system." Physical Review B 43 (1991): 5430.
Abstract: Lowtemperature specificheat C measurements as a function of temperature T between 0.5 and 30 K are reported for Y1xPrxBa2Cu3O7δ compounds with x=0, 0.2, 0.3, 0.4, 0.6, 0.8, and 1.0. The Pr contribution to the specific heat of all of the samples can be described as the sum of a Pr nuclear Schottky anomaly of the form CN(T)=AT2, a linear term CL(T)=γT, and a Pr magnetic anomaly. For compounds with x≤0.6, which are metallic and superconducting, the Pr magnetic specificheat anomaly has the same temperature dependence as a Kondo anomaly. For the compounds with x≥0.8, which are insulating, the magnetic specificheat anomaly is consistent with antiferromagnetic ordering of the Pr ions with Néel temperatures TN of 10.9 and 15.7 K for x=0.8 and 1.0, respectively. For T<TN, the antiferromagnetic specificheat anomaly has the form CM(T)=MT3, characteristic of threedimensional antiferromagnetic magnons.

Nieva, G., B. W. Lee, J. Guimpel, H. Iwasaki, M. B. Maple, and I. K. Schuller. "Changes in the Prinduced TC depression of 123 compounds by chemical pressure." Physica C: Superconductivity 185189, no. 1 (1991): 561–562.
Abstract: We present structural data refined from Xray spectra for R1−xPrxBa2Cu3O7−δ (R=Er, Gd, Eu, Sm, Nd) systems with x=0, 0.1, and 0.4. The evolution of Tc with the ionic radius of the rare earth for different values of x can be related to the Cu2O4 distance. The effect of chemical pressure on Tc in R1−xPrxBa2Cu3O7−δ systems is opp osite to that of hydrostatic pressure on the Y1−xPrxBa2Cu3O7−δ system.

Nieva, G., S. Ghamaty, B. W. Lee, M. B. Maple, and I. K. Schuller. "Superconductivity and magnetism in Eu1xPrxBa2Cu3O7δ." Physical Review B 44 (1991): 6999.
Abstract: Measurements of the electrical resistivity ρ as a function of temperature T, and lowtemperature specific heat C as a function of T and magnetic field H, have been performed for Pr concentrations 0≤x≤1 in the Eu1xPrxBa2Cu3O7δ system (δ≊0.05). The superconducting critical temperature Tc(x) in the metallic phase (0≤x≲xc≊0.5) was determined from the resistivity ρ(x,T), while the Néel temperature TN(x) in the insulating phase (xc≲x≤1) was inferred from specificheat anomalies due to antiferromagnetic (AFM) ordering of the Pr ions. The effect of ‘‘chemical’’ pressure on Tc(x) in the Y1xPrxBa2Cu3O7δ system is opposite to that of applied hydrostatic pressure. The Pr contributions to the specific heat in the insulating phase have the form C(T)=MT3 for T<TN, characteristic of threedimensional AFM magnons. In contrast, the Pr contribution to C(T) in the metallic phase takes the form of a broad anomaly that can be described by a spin1/2 Kondo model. The entropy associated with the Pr specificheat anomalies in both the metallic and insulating phases is close to R ln2, indicative of a doublet ground state for Pr in the crystalline electric field and a Pr valence close to 4+.
