LAYER-RIGIDITY MODEL AND THE MECHANISM FOR ION-DIFFUSION-CONTROLLED KINETICS IN THE BISMUTH CUPRATE 2212-TO-2223 TRANSFORMATION

Recent transmission electron microscopy (TEM) experiments have shown that the transformation of the Pi cuprate 2212 phase to 2223 phase consists of fast growth of Ca/CuO2 planes in the Bi-2212 matrix. A theory is proposed which considers the cylindrical void created by the edge dislocation due to the insertion of a Ca/CuO2 plane to be a channel for fast ion diffusion. A layer-rigidity model is used to estimate the size of the void for Bi-2212/Bi-2223, as well as that for the stacking fault created by heavy-ion irradiation in YBa2Cu3O7 (YBCO) compounds. We find the predictions of the model to agree quantitatively with TEM measurements of the structures of ion-irradiated YBCO systems. The calculated void size for Bi-2212/Bi-2223 compounds is consistent with the existence of fast ion diffusion along the ab plane. The experimentally observed time dependence of the volume fraction of Bi-2223 during the transformation is found to be consistent with a one-dimensional diffusion-controlled transformation mechanism, as predicted by our model.