PERCOLATION OF LINEAR CLUSTERS IN YBA2CU3OX - A TOOL FOR EXPLAINING THE ORTHO-TETRAGONAL PHASE-TRANSITION

The recent experimental results on the dependence of the oxygen content versus the temperature and the oxygen partial pressure show that orthorhombic-tetragonal transition occurs for x>6.6 with T>814 K. We deduce from molecular arguments that linear chains are favoured even in the tetragonal phase. Then, by applying the percolation theory we re-find the transition at 6.67. The consequence of such a computation is the knowledge of the cluster population, a quantity useful for interpreting the electron-transport properties. © 1990.