OXYGEN ORDERING AND CHAIN FORMATION IN YBA2CU3OZ

A distinctive aspect of the thermodynamic properties of YBa2Cu3O2 is t he basal-plane oxygen ordering which leads to the formation of Cu-O ch ains and the development of orthorhombic phases. Theoretically, this p henomenon may be explained in terms of an Ising Hamiltonian with two t ypes of second-neighbor interactions (ASYNNNI model). This symmetry br eaking and ground-state degeneracy lead to kinetically arrested multi- domain structures. This paper reports new simulation results for these mesoscopic features, with specific emphasis on the effects of dopants , elastic deformation, and possible structural phase separation.