Oxygen dependence on superconducting properties of La1.85Sr0.15CuO4-δ ceramic and crystal samples

We have produced LSCO ceramic samples by a sol-gel method, whose high quality is demonstrated by NQR and specific heat measurements. Many studies concerning the influence of phase purity, strontium, homogeneity and oxygen stoichiometry on the superconducting properties of La1.85Sr0.15CuO4-delta were carried out using X-ray diffraction, SQUID magnetization and specific heat measurements. The control of strontium and oxygen content achieved on ceramic samples gave us the opportunity to optimize our LSCO 'crystal' grown by the travelling solvent floating zone method. Low-temperature specific heat measurements were also performed between 0.3 and 8 K on both La1.85Sr0.15CuO4, ceramic and 'crystal' samples in the T-range 0.3-8 K and the results revealed that the specific heat residuals of our samples were lower than those already measured and published by other groups. (C) 1998 Elsevier Science B.V.