Synthesis and characterization of perovskite-phase mixed-metal oxides: lead titanate

Abstract

The reaction of Pb(O₂CCMe₂OH)₂ and (acac)₂Ti(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(O₂CCMe₂O)₂Ti(acac)₂·xC₅H₅N]. This species can act as a single-source precursor to PbTiO₃. ¹H 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(O₂CCMe₂O)₂Ti(acac)₂] does not react with HOPrⁱ, indicating that this reaction is irreversible. Thermolysis of [Pb(O₂CCMe₂O)₂Ti(acac)₂] results in loss of the organic ligands and the initial formation of amorphous material. Part of this amorphous material crystallizes at 310 °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 °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 perovskitephase PbTiO₃ at 410 °C. Analytical data (atomic absorption spectroscopy) were consistent with a 1 : 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 pyrochlorephase PbTiO₃ does not transform into crystalline perovskite-phase PbTiO₃ under these conditions.