Dependence of perovskite/pyrochlore phase formation on oxygen stoichiometry in PLT thin films
- PDF / 1,125,640 Bytes
- 13 Pages / 612 x 828 pts Page_size
- 88 Downloads / 171 Views
Thin films in the P b - L a - T i - O (PLT) system were prepared under two different oxygen partial pressure (Po 2 ) conditions by multi-ion-beam reactive sputtering (MIBERS). The oxidation of the depositing species was determined from the deposition rate dependence on POl and the POl dependence of the positive secondary ion emission from the sputtering targets. Films deposited at high POl {POl 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 (POl 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 POl 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.
I. INTRODUCTION Formation of the metastable nonferroelectric pyrochlore phase has typically been a great hindrance in the preparation of ferroelectric Pb-based perovskite thin films made by various methods. Many researchers have reported that the pyrochlore phase can be converted to the ferroelectric phase by adjusting the Pb stoichiometry,1'2 increasing the deposition temperature,3'4 or increasing the postdeposition annealing temperature and time.5'6 Each of these processing variables modifies the reaction kinetics and therefore affects the phase formation or the conversion of pyrochlore to perovskite. The influence of the reaction kinetics on the formation of pyrochlore has been confirmed in bulk materials prepared from mixed oxides; the formation of pyrochlore can be reduced by altering the reaction sequence, which results in a change in the reaction rates of the oxide precursors.7'8 This paper presents evidence indicating that the perovskite/pyrochlore phase formation in PLT thin films deposited by multi-ion-beam reactive sputtering (MIBERS) is controlled by the oxidation state of the lead in the as-deposited film. With the MIBERS technique, metal targets of Pb, La, and Ti are reactively sputtered in an oxygen atmosphere. Oxide formation at the surfaces
a)
Present address: Ecole Polytechnique Federale de Lausanne, Laboratoire de Ceramique, MX-D Ecublens, CH-1015, Lausanne, Switzerland. J. Mater. Res., Vol. 9, No. 3, Mar 1994
http://journals.cambridge.org
Downloaded: 14 Mar 2015
of the metal targets depends on the thermodynamic tendency of the metal to form an oxide, the partial pressure of oxygen (Po2), a n d m e relative rate of sputtering, which is controlled by incident ion f
Data Loading...
