Encapsulated Single Crystal Growth and Annealing of the High-Temperature Superconductor Tl-2201

TL;DR

This paper reports a novel encapsulation method for growing high-quality Tl-2201 single crystals, enabling controlled annealing and detailed characterization of their structural and superconducting properties.

Contribution

A new encapsulation scheme for growing and annealing high-quality Tl-2201 single crystals with improved purity and structural characterization.

Findings

Crystals exhibit sharp superconducting transitions

Crystals have narrow X-ray rocking curves

Observation of a new commensurate superlattice distortion

Abstract

Highly-perfect platelet single crystals of Tl_2Ba_2CuO_{6+d} (Tl-2201) were grown by a self-flux technique. A novel encapsulation scheme allowed the precursors to react prior to the sealing required to contain volatile thallium oxides, and permitted the removal of melt at the conclusion of growth, reproducibly producing high yields of clean crystals. The crystals were annealed under well-controlled oxygen partial pressures, then characterised. They have sharp superconducting transitions, narrow X-ray rocking curves and a low 4% substitution of thallium by copper, all evidence of their high perfection and homogeneity. The crystals are orthorhombic at most dopings, and a previously unreported commensurate superlattice distortion is observed.