Comments on the phase diagrams and crystallisation paths of Y-Ba-Cu-O materials

Our microstructural characterisation of Y-Ba-Cu-O quenched partial melts sh ows that the BaCuO2 (BC1) phase is crystalline at temperatures as high as 1 100 degrees C, and that the partial melt self-establishes a microstructural gradient from the surface towards the interior of the samples, which can b e associated with a gradient in an equivalent partial pressure of O-2 (pO(2 )). The extension of the Y2BaCuO5-YBa2Cu3O7-x (Y211-Y123) tie-line intersec ts the primary crystallisation field of BC1 first. The actual peritectic re action that takes place is Y2BaCuO5(s)+ BaCuO2(s) + 2BaCu(2)O(2(L)) + 1/2O(2) --> 2YBa(2)Cu(3)O(6(s)). Two schematic representations which allow an analysis of the pO(2) dependen ce are given. The gradient in microstructure self-established by the sample acts as a driving force for texturing. With this new perspective gained ab out the actual peritectic reaction and mechanisms of melt-texturing of Y123 , it is possible to explain most of the aspects about partial melt-texturin g. In addition, it seems possible to devise heat treatments that may allow for the production of well-oriented single domains with very large diameter s. (C) 1999 Elsevier Science B.V. All rights reserved.