Laser-deposited epitaxial thin films of Cu3Ba2YO7 were investigated by means of high-resolution transmission electron microscopy. This revealed the presence of narrow layers of Cu4Ba2YO8. Within the CuO double layers of this phase, columns of double Cu(I) vacancies were found to occur at periodic spacings which were twice the a-axis lattice parameter. An interchange of the a- and b-axes was observed upon traversing the c-axis.

N.D.Zakharov, G.Kästner, D.Hesse, M.Lorenz: Applied Physics Letters, 1996, 69[8], 1151-3