New understanding of silver-induced texture in powder-in-tube processed Ag/Bi(2223) tape

Silver-sheathed bismuth-based (Bi,Pb)(2)Sr2Ca2Cu3Ox(2223) tape is prepared by the powder-in-tube process from a precursor powder which consists of (Bi,Pb)(2)Sr2CaCu2Ox(2212), (Ca,Sr)(2)PbO4, Ca2CuO3, CuO, (Ca,Sr)(14)Cu24O41, Bi-2(Sr,Ca)(x)CuOx(2201). Silver layers are found to greatly promote the formation and texturing of the 2223 phase. The evidence is defined as silver-induced texture (SIT). The previously defined reaction-induced texture (RIT) for the 2223 phase is also confirmed at the same time. The Pb loss is appreciable due to the removal of the broad silver layers while the Pb loss is negligible when only the lateral layers are removed. X-ray photoelectron spectroscopy (XPS) shows that Pb4+ released from Ca2PbO4 enters the BiO plane of the 2212 phase to replace Bi3+ as Pb2+ to make 2223 nucleate. Auger electron spectroscopy (AES) depth profile analysis shows that the oxygen out-diffusion through the silver sheath is very rapid. The mechanism of SIT is proposed to be a combined effect of preventing Pb loss the during high temperature reaction to 2223, supplying a fast out-diffusion path for oxygen produced during 2212 to 2223 transformation, inducing liquid formation to accelerate atomic diffusion, and preferably promoting plate-like grain growth with the a-b plane parallel to the broad layer by a quasi-two-dimensional space. (C) 1997 Elsevier Science B.V.