Dependence of perovskite/pyrochlore phase formation on oxygen stoichiometry in PLT thin films

Abstract

Thin films in the Pb-La-Ti-O (PLT) system were prepared under two different oxygen partial pressure (PO₂) conditions by multi-ion-beam reactive sputtering (MIBERS). The oxidation of the depositing species was determined from the deposition rate dependence on PO₂ and the PO₂ dependence of the positive secondary ion emission from the sputtering targets. Films deposited at high PO₂ (PO₂ greater than the critical partial pressure for oxidation of the Pb target surface) were fully oxidized, and they formed the pyrochlore phase during annealing. The low PO₂ conditions (PO₂ less than or equal to the critical partial pressure for oxidation of the Pb target surface) caused sputtering of incompletely oxidized Pb species, and the resulting oxygen deficient films produced phase-pure perovskite. The formation of the pyrochlore phase at high PO₂ and the perovskite phase at low PO₂ is independent of Pb content within the film; the phase formation is dependent on the oxidation state of the Pb, which is sensitive to both the PO₂ and the sputtering rate of the Pb. A perovskite/pyrochlore phase formation model (PPFM) that incorporates annealing time, temperature, and heating rate, and thin film oxygen deficiency was developed to explain the formation of the perovskite and pyrochlore phase during postdeposition annealing of PLT thin films.