Single-crystal growth and characterization of the superconductor HgBa2CuO4+δ

Single crystals of HgBa2CuO4+δ of typical size 350x350x50 μm3 were grown inside a sealed silica tube with and without excess of precursor Ba2CuO3+y. The process is reproducible for high growth temperatures (T > 1050 deg. C) at which the use of an alumina crucible is necessary. For lower growth temperatures the as-prepared crystals are underdoped with 83 ≤ Tc ≤ 91 K. An optimal Tc is achieved by post-annealing the crystals in flowing oxygen at 300 deg. C. Crystals grown at higher temperatures show an increase of the c-axis length after oxygen annealing, indicating they are overdoped. (author)