SYNTHESIS AND CHARACTERIZATION OF PEROVSKITE-PHASE MIXED-METAL OXIDES- LEAD TITANATE

The reaction of Pb(O(2)CCMe(2)OH)(2) and (acac)(2)Ti(OPri)(2), where a cac=CH3COCHCOCH3, in a 1:1 stoichiometry results in elimination of two equivalents of HOPri and formation of a species with empirical formul a [Pb(O(2)CCMe(2)O)(2)Ti(acac)(2).xC(5)H(5)N]. This species can act as a single-source precursor to PbTiO3. H-1 NMR studies of the formation of this species in pyridine reveal that the alkoxide ligands are comp letely eliminated and that the reaction appears to occur in two steps. The species [Pb(O(2)CCMe(2)O)(2)Ti(acac)(2)] does not react with HOPr i, indicating that this reaction is irreversible. Thermolysis of [Pb(O (2)CCMe(2)O)(2)Ti(acac)(2)] results in loss of the organic ligands and the initial formation of amorphous material. Part of this amorphous m aterial crystallizes at 310 degrees C with 2 nm sized crystallites whi ch can be attributed to the presence of either pyrochlore-phase PbTiO3 or PbO, based on powder X-ray diffraction data. When the sample is he ated further to 330 degrees C, the remainder of the amorphous material starts to crystallize as perovskite-phase PbTiO3 with a much larger c rystallite size of 30 nm. X-Ray powder diffraction and transmission el ectron microscopy data are consistent with the presence of a small amo unt of 2 nm sized crystallites in perovskite-phase PbTiO3 at 410 degre es C. Analytical data (atomic absorption spectroscopy) were consistent with a1:1 Pb:Ti atomic ratio, which we interpret as being more consis tent with the presence of pyrochlore-phase PbTiO3 than PbO. We believe that there is little or no phase transformation under these condition s. As a result we conclude that single-source precursors to PbTiO3 res ult in lower crystallization temperatures than multiple sources of Pb and Ti and that pyrochlore-phase PbTiO3 does not transform into crysta lline perovskite-phase PbTiO3 under these conditions.