Synthesis of high- <i>T</i> c Y-based cuprate superconductors with <i>T</i> c = 130 K using high-pressure synthesis method accompanied with shear stress

We successfully synthesized a metastable phase of Y-based cuprate superconductors with an onset Tc of 130 K using a high-pressure torsion (HPT) synthesis method, in which intense shear stress was applied under high-pressure compression. A mixture of copper oxide, yttrium oxide, and barium oxide was subjected to HPT processing and subsequently annealed at low temperatures. The HPT processing generated seed crystals of Y-based cuprates, while the low-temperature annealing enlarged the superconducting grains. In addition, the annealing modified the oxygen concentration, stabilizing the metastable structure and inducing further carrier doping. As a result, magnetic shielding signals with the onset Tc of 130 K were detected through magnetic measurements. The value exceeds the Tc = 93 K of optimally doped YBa2Cu3O7−δ synthesized via a conventional high-temperature solid-state reaction. The expanded unit-cell feature of YBa2Cu3O7−δ was confirmed through structural analyses. It is necessary to examine how variations in the apical-oxygen distance relative to the CuO2 plane influence the superconducting properties.