AN INVESTIGATION OF THE INVARIANT REACTIONS IN THE BIPHSRCACUO SYSTEM

The phases present around the (Bi,Pb)(2)Sr2Ca2Cu3Ox (2223) phase betwe en 830-880 degrees C have been studied by x-ray diffraction (XRD) and electron probe microanalysis (EPMA) methods. The decomposition and mel ting temperatures of the 2223 phase in these samples have been measure d by the differential thermal analysis (DTA) method. Partial substitut ion of Bi with Pb (Pb:Bi = 3:22) does not change the 850 degrees C pha se relations around 2223 phase. 2223 decomposes to liquid, Sr7Ca7Cu24O 41 (7724), and Ca2CuO3 at 875 degrees C. The invariant reactions (degr ee of freedom is zero) among 2223, 7724, Ca2CuO3, CuO, Bi2Sr2CaCu2O8 ( 2212), and liquid were proposed to be L + 7724 + Ca2CuO3 --> 2223 + 22 12, L + 7724 + Ca2CuO3 --> 2223 + CuO, L + 7724 --> 2223 + 2212 + CuO. The reaction temperatures were estimated to be 860 degrees C, 860 deg rees C, and 854 degrees C, respectively. An invariant reaction scheme and a tentative liquidus projection were sketched out.