Crystal growth and superconductivity of (La1−xCax)2CaCu2O6+δ

The effects of growth conditions and composition on the crystal growth of (La1−xCax)2CaCu2O6+δ (x=0.05–0.15) superconducting materials have been studied by using the floating zone method. A smooth solid-liquid growth interface of (La1−xCax)2CaCu2O6+δ (x=0.05–0.06) tended to break down into a cellular interface when the growth velocity was higher than 0.5mm/h. When the solid–liquid interface became cellular, the single crystal size in an as-grown rod decreased abruptly and the as-grown rod was not single phase. Various sized CaO inclusions were found inside the as-grown single crystals of (La1−xCax)2CaCu2O6+δ (x≥0.075). Cubic centimeter size single crystals were successfully grown for both (La0.95Ca0.05)2CaCu2O6+δ and (La0.94Ca0.06)2CaCu2O6+δ. The as-grown single crystals of (La1−xCax)2CaCu2O6+y under 1bar pressure of oxygen were not superconducting. The superconducting temperature of the (La1−xCax)2CaCu2O6+y crystals grown at 11bar oxygen is 28K. The application of high pressure oxygen during crystal growth is an effective method to get bulk superconductivity in the crystals.