Synthesis of high quality thallium superconductors at elevated oxygen pressure

Abstract

Preparation of thallium superconductors at pressures up to 200 bar is reported. We find that thallium loss can be completely suppressed, so that samples can be heated for long durations to ensure complete reaction and densification without loss of thallium. The relative phase fractions of Tl₂Ba₂CuO₆ (2201), Tl₂Ba₂Ca₁Cu₂O₈ (2212) and Tl₂Ba₂Ca₂Cu₃O₁₀ (2223) are found to depend upon (a) starting composition ( b ) temperature of reaction/sinter(c) total pressure and (d) oxygen partial pressure. Phase fractions were determined by X-ray powder diffraction. SQUID magnetization data reveal high superconducting volume fraction and sharp transitions. These dense, textured, polycrystalline high temperature superconductors show high critical current values (determined magnetically) which approach those of single crystal and oriented thin films.