Support-promoted stabilization of the metastable PZT pyrochlore phase by epitaxial thin film growth

Thin films of lead zirconium titanium oxide with the Zr/Ti ratio close to 5 2/48 have been grown by pulsed laser deposition on epitaxial (100)CeO2 buff ered R-plane sapphire substrates, Instead of the expected perovskite struct ure, these films are pure cubic metastable pyrochlore phase, From X-ray dif fraction in theta -2 theta mode and theta -scans it appears than the films are fully {100} oriented with a mosaicity in the range 0.8 degrees -0.9 deg rees, In-plane characterizations, including RHEED photographs, electron-cha nneling patterns, XRD P-scans, and near grazing incidence XRD, are indicati ve of high-quality epitaxial growth, cube-on-cube, on the CeO2 sublayer, RE S analyses show that increasing the deposition temperature in the range 560 -650 degreesC does not affect the Zr/Ti ratio, white the lead content drops significantly from Pb/(Zr+ Ti) = 0.7 to 0.3 (a stoiehiometry close to the composition of ''Pb(Zr0.52Ti0.48)(3)O-7"); simultaneously, the unit-cell co nstant decreases monotically from 10.40 to 10.15 Angstrom. A comparison wit h results obtained on a variety of other substrates suggests that the drivi ng forte that imposes the growth of the pyrochlore phase at the expense of the perovskite-like one is not related to the misfit, but to the nature of the interface at the atomic scale, due to the close structural relations be tween fluorite and pyrochlore. This hypothesis is confirmed by the obtentio n of the usual perovskite variant when a (111)CeO2 sublayer is used. (C) 20 01 Academic Press.