Successful synthesis of Hg0.80Re0.20Sr2Can-1CunO2n+2+delta (n = 1, 2) by the sealed quartz tube technique

Ba-free Hg,Re-1201 and -1212 were prepared by the sealed quartz tube techni que. The starting materials were nominal precursor Re0.20Sr2CanCun-1Ox (n = 1, 2) and HgO. The unreacted pellets were annealed at 750 degrees C for 12 h for the n = 1 member and 850 degrees C for 12 h for the n = 2 member. Ri etveld structural refinement was performed with the X-ray diffraction patte rns, including impurity phases if needed. Both phases showed SG P4/mmm (nr. 123). Fitted tetragonal cell parameters were a = b = 3.7822(1) Angstrom, c = 8.8776(5) Angstrom and a = b = 3.8205(3) Angstrom, c = 12.0438(8) Angstr om for the n = 1 and n = 2 members, respectively. DCSQUID (Superconducting Quantum interference Device) magnetometry and AC susceptibility were used t o measure the superconducting properties of the samples. We also studied th e effect of post-treatments in oxygen and argon. No superconductivity was f ound for the n = 1 in any case. However, T-c,T-onset as high as 107 K was d etermined for the Hg,Re-1212. (C) 1998 Kluwer Academic Publishers.