Heat Treatment Effect on Superconductivity and Specific Heat of Pr_1.85Ce_0.15CuO_4+δ

Abstract

Polycrystalline samples of electron-doped Pr 1.85 Ce 0.15 CuO 4+δ have been prepared under different annealing conditions and investigated by X-ray diffraction analysis, oxygen content analysis, electrical resistivity, magnetic susceptibility and low-temperature specific heat measurements. X-ray-diffraction patterns show that the samples contain a single T' phase. The superconducting transition temperatures T cm taken with the onset of diamagnetism in magnetic-susceptibility measurements are 20 and 19.5 K for the samples annealed in flowing Ar gas and in vacuum (∼10 -3 Torr), respectively. The data of the samples annealed in flowing Ar gas show clear evidence of α T 2 term at zero magnetic field in superconducting electronic specific heat, and are consistent with d -wave superconductivity. However, this behavior is not observed in the other sample, which is annealed in vacuum. These results indicate that different heat treatments affect the oxygen content, homogeneity, superconducting transition temperature T c , superconducting volume fraction, and the superconducting pairing symmetry of Pr 1.85 Ce 0.15 CuO 4+δ . We also discuss the results of specific heat in La 2- x Sr x CuO 4 ( x =0.1, 0.16 and 0.22) to explain these behaviors observed in the specific heat of Pr 1.85 Ce 0.15 CuO 4+δ .