On the flux growth and some properties of superconducting YBa2Cu3O7-ϰ single crystals and LPE films

Abstract

DTA and crystal growth experiments were applied in order to determine the primary crystallization field of YBa2Cu3O7-ϰ in BaO-CuOx-YO1.5 flux melts for crystal growth and liquid phase epitaxy (LPE). Simultaneous thermogravimetric (TG) and DTA experiments prove an essential reduction of CuO to Cu2O during heating; the complete reduction of Cu2+ occurs at 1026°C. In the presence of alkaline earth oxides CaO, SrO, and BaO a decreasing temperature for Cu2+ reduction and melting is found. Reduced oxygen partial pressure results in a higher Cu+ concentration and in lower crystallization temperatures as well as lower eutectic ones. Crystal growth experiments under isothermic conditions at about 900°C have been carried out, where the supersaturation is produced by an increasing oxygen partial pressure. X-ray diffraction, electron microanalytic, polarization microscopic, and magnetic measurements prove the LPE growth of twinned c-YBa2Cu3O7-ϰ films on (001) LaGaO3 substrates and of twinned a,b films on (110) NdGaO3 substrates. Relatively smooth films with planar defects and thicknesses of 5-10 μm were grown by this vertical LPE technique.