TRIAXIALLY ORIENTED GROWTH OF CUO ON MGO (001) - X-RAY-DIFFRACTION STUDIES OF PURE CUO FILMS AND INCLUSIONS IN SUPERCONDUCTING Y-BA-CU-O FILMS PREPARED BY MOCVD

We present results on MOCVD-grown CuO films and superconducting YBa2CU3O7-delta films containing CuO inclusions. The films discussed in detail were deposited on MgO (001) substrates, at 690-degrees-C, under O2 partial pressures of 11-17 Torr. Various X-ray diffraction methods were used for film characterization, including phi-scan measurements sensitive to the in-plane orientation of the monoclinic CuO phase. These were augmented by scanning electron microscopy and electron probe microanalysis studies. Our CuO films show extreme orientation of CuO (111)\\MgO (001). They are also characterized by one predominant type of in-plane orientation, CuO [110BAR]\\MgO [110], and display substrate-induced twinning. We rationalize the preferred azimuthal orientation for CuO films in terms of a simple geometrical lattice match, and compare our results with previous reports on CuO growth on MgO (001). The YBa2CU3O7-delta films typically show zero d.c. resistance at approximately 80 K, are highly oriented with YBa2CU307-delta (001)\\MgO (001), and also show in-plane alignment consistent with other studies. CuO inclusions with diameters of 0.3-1.5 mum occur at typical densities of approximately x 10(7) cm-2, and predominantly nucleated at the substrate surface. We show that the CuO inclusions display the same type of triaxial orientation as our pure CuO films by means of phi-scan measurements, and comment on the difficulty in detecting (111)-oriented CuO by the theta-2theta technique. Finally, we discuss preliminary results confirming that the formation of triaxially oriented CuO is very specific to the MgO (001) surface, and deposition conditions favouring initial growth of CuO rather than Cu2O.