Thermodynamic properties of superconducting and non-superconducting Pr2Ba4Cu7O15-δ15-δ compounds with metallic double chains

• This manuscript covers the thermodynamic properties of the superconducting and non-superconducting Pr2Ba4Cu7O15-δ compounds with metallic CuO double chains.
• The specific heat data of the superconducting sample exhibited no obvious superconducting anomaly but a Schottky like broad maximum appeared at low temperatures.
• The Schottky like anomaly was attributed to low-lying quasi-triplet splitting of Pr3+3+ ions under the crystal field effect.

To examine the thermodynamic properties of Pr2Ba4Cu7O15-δ15-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-λ-like enhancement in the specific heat measurement appeared near the antiferromagnetic transition temperature TN=17TN=17 K. In contrast, the reduced superconducting sample with Tcon=26.5 K exhibited no obvious superconducting anomaly in its specific heat data, but a Schottky-like broad maximum appeared at low temperatures. The Schottky-like anomaly was attributed to low-lying quasi-triplet splitting of Pr3+Pr3+ ions under the crystal field effect.