Use of a fluorine-containing solvent in the synthesis of YBa2Cu3O7 − δ single crystals

A laboratory technological procedure has been developed for the synthesis of high-temperature superconducting YBa2Cu3O7 − δ single crystals (T c ∼ 90 K, ΔT c ∼ 1.0 K) up to 0.25 cm2 in size from a nonstoichiometric fluorine-containing flux of (YO1.5)(BaO)4 − x(BaF2)x(CuO)10, where 2 ≥ x ≥ 0, using a combination of enhanced nucleation and directional crystallization by the Czochralski method. Studies using differential thermal analysis demonstrated that the addition of BaF2 decreased the eutectic-crystallization temperature and increased the crystal-growth rate. The optimum concentration of BaF2 in the starting melt composition was found (x = 0.2). The single-crystal surface was studied by atomic-force nanoscopy. The morphology of single crystals that have been synthesized from a melt of their own components differs substantially from that of crystals grown from a BaF2-containing melt.