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 acac=CH3COCHCOCH3, in a 1:1 stoichiometry results in elimination of two equivalents of HOPri and formation of a species with empirical formula [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 completely 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 HOPri, 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 material crystallizes at 310 degrees C with 2 nm sized crystallites which can be attributed to the presence of either pyrochlore-phase PbTiO3 or PbO, based on powder X-ray diffraction data. When the sample is heated further to 330 degrees C, the remainder of the amorphous material starts to crystallize as perovskite-phase PbTiO3 with a much larger crystallite size of 30 nm. X-Ray powder diffraction and transmission electron microscopy data are consistent with the presence of a small amount of 2 nm sized crystallites in perovskite-phase PbTiO3 at 410 degrees C. Analytical data (atomic absorption spectroscopy) were consistent with a1:1 Pb:Ti atomic ratio, which we interpret as being more consistent with the presence of pyrochlore-phase PbTiO3 than PbO. We believe that there is little or no phase transformation under these conditions. As a result we conclude that single-source precursors to PbTiO3 result in lower crystallization temperatures than multiple sources of Pb and Ti and that pyrochlore-phase PbTiO3 does not transform into crystalline perovskite-phase PbTiO3 under these conditions.