SOLIDIFIED PRODUCT FROM Bi-Sr-Ca-Cu-O MELT AND ITS TRANSFORMATION INTO SUPERCONDUCTOR

The Bi_2(Sr,Ca)_3Cu_2O_x system superconductor was prepared by different melting proceduresand after treatment.The effects of cooling rate,annealing temperature and time,as well asmelting procedures on phase transformation were investigated.The structure and propertieswere examined by X-ray diffraction,optical microscopy,EPMA,DTA,TGA andmeasurements of electric and magnetic properties.When the melt of nominal compositionBi_2(Sr,Ca)_3Cu_2O_x solidified in air,the Bi_2(Sr,Ca)_3Cu_2O_(8+δ)(2212)superconducting phase isstable,the easily solidified product including Bi_2(Sr,Ca)_2CuO_(6+δ)(2201)phase is metastable,and another may be amorphous if rapidly quenched.The last two may transform into 2212phase by after treatment at an optimal annealing temperature ranging 780—870℃.While2201 phase,prepared by the laser floating zone melting method,may easily transform into2212 phase at layer or filament in shape which is favourable to improve the links amongsuperconducting grains and critical current density.