Bulk synthesis of the 135 K superconductor HgBa₂Ca₂Cu₃O_8+δ

Bulk synthesis of the high‐temperature superconductor HgBa₂Ca₂O_8+δ (Hg‐1223)—an important step towards realizing its technological potential—is described. In the reaction discussed, the formation of bulk samples (up to 20 g) with excellent phase purity and transition temperatures above 130 K at ambient pressure proceeds from the binary oxides by a solid‐state route. The significant advantages of this method compared to the high‐pressure routes currently used are pointed out.