Self-adjusted flux for the traveling solvent floating zone growth of YBaCuFeO5 crystal

• Large size and high quality single crystal of YBaCuFeO5 was grown using a modified traveling solvent floating zone (TSFZ) method.
• The TSFZ growth uses pure CuO as the initial flux for the incongruently melting YBaCuFeO5 without relying on a phase diagram.
• A partial pseudo-binary phase diagram of YBaCuFeO5-CuO has been constructed based on the chemical analysis of solidified flux.
• Adding 2 wt% B2O3 into the solvent rod can increase the viscosity and stability of the molten zone.

A modified traveling solvent floating zone (TSFZ) technique was used to successfully grow a large size and high quality single crystal of multiferroic material YBaCuFeO5. This modified TSFZ growth uses a stoichiometric feed rod and pure copper oxide as the initial flux without prior knowledge of the complex phase diagram involving four elements, and the optimal flux for the growth of incongruently melt crystal is self-adjusted after a prolonged stable pulling. The wetting of the feed rod edge that often perturbs the molten zone stability was avoided by adding 2 wt% B2O3. The optimal flux concentration for the YBaCuFeO5 growth can be extracted to be near YBaCuFeO5:CuO=13:87 in molar ratio. The crystal quality was confirmed by the satisfactory refinement of crystal structure of space group P4mm and the two consecutive anisotropic antiferromagnetic phase transitions near 455 K and 170 K.