Thermodynamic properties of superconducting and non-superconducting Pr2Ba4Cu7O15-δ compounds with metallic double chains

Abstract

To examine the thermodynamic properties of Pr2Ba4Cu7O 15−δ compounds with metallic CuO double chains, we measured the specific heats of superconducting and non-superconducting polycrystalline samples at low temperatures (1.8-40 K) under various magnetic fields (up to 9 T). In the as-sintered non-superconducting sample, a λ−like enhancement in the specific heat measurement appeared near the antiferromagnetic transition temperature TN = 17 K. In contrast, the reduced superconducting sample with Tc,on = 26.5 K exhibited no obvious superconducting anomaly in its specific data, but a Schottky-like broad maximum appeared at low temperatures. The Schottky-like anomaly was attributed to low-lying quasi-triplet splitting of Pr 3+ ions under the crystal field effect.