Phase composition of the rapidly quenched melt of YBa 2Cu 3O 7− y+20 mol% Y 2BaCuO 5

Abstract

Samples of YBa 2Cu 3O 7− y +20 mol% Y 2BaCuO 5, with thicknesses ranging between 50–250 μm, have been melt processed and rapidly quenched from temperatures between 985 and 1100°C by immersing them in liquid nitrogen. The phase composition and microstructures of these samples have been characterised using a combination of X-ray diffractometry, optical microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy. The quenched melt of samples quenched from temperatures greater than 985°C appears relatively homogeneous but consists of Ba 2Cu 3O x (BC1.5) and BaCu 2O 2 (BC2) regions. At about 985°C, BaCuO 2 (BC1) crystallises from the melt and most of the BC1.5 decomposes into BC1 and CuO or into BC1 and BC2. The crystallisation of BC1 induces segregation of elements in the melt and this is very significant for the melt texturing of YBCO.