Encapsulation method for the synthesis of nearly single-phase superconducting HgBa₂Ca₂Cu₃O_8+δ with T_c≥ 135 K

Nearly single-phase polycrystalline samples of HgBa₂Ca₂Cu₃O_8+δ were successfully synthesized under relatively simple and unprecedented synthesis conditions, i.e. at a "low" temperature (<700°C) and for a "long" period of time (5-168h), using mono-oxide powders of Hg, Ba, Ca, and Cu as starting materials. A pressed powder mixture was heated at 665°C for ≈75 h in an evacuated fused quartz tube, and then post-annealed in flowing O₂ gas to exhibit a Meissner signal below 135.4 K. Zero resistance of this sample was observed at 133.9 K.