Controlling piezoelectric properties through grain orientation in tapecast PZT multilayers

The synthesis of perovskite xNa0.5Bi0.5TiO3-(1-x)PbTiO3 (NBT-PT) templates via topochemical conversion of Aurivillius phase PbBi4Ti4O15 (PBT) precursor is explored. Significant template particle defects, difficulty in reproducing desired grain morphologies, and the complexity of the synthesis procedure necessitates the use of commercially available BaTiO3 (BT) templates as a suitable alternative. Successful templated grain growth (TGG) of [001]-textured Pb(ZrxTi1-x)O3 (PZT) multilayers using 5 vol. % anisometric (001) BT templates + 5 wt. % PbO (PZTx-5BT), along with TGG of [001]-textured commercial PZT-5A1 composition using 10 vol. % anisometric (001) BT templates is presented. The critical processing parameters necessary to achieve texturisation in PZT multilayers are investigated, along with further compositional tailoring of the PZTx-5BT system considering both compositional and piezoelectric effects of the added BT templates within the PZT system. Nanoscale PZT powder is mixed with 5 wt. % PbO, to act as a transient liquid phase during sintering and promote textured grain heteroepitaxy. Anisometric (001) BT platelet shaped seed crystals are added into the PZT slurry and aligned during tapecasting. The tape is sectioned, stacked, and pressed into green bodies prior to binder burnout. During sintering, [001]-textured PZT grains nucleate on the (00l) crystal faces of the oriented template grains and grow at the expense of the finer matrix material via Ostwald ripening, followed by exaggerated grain growth. The resulting multilayer exhibits texture in the [001] direction. PZT multilayers synthesised with 5 vol. % BT templates + 5 wt. % PbO achieve a Lotgering factor, f(001) ~ 0.94, indicating near complete [001]-texturisation. Commercially available PZT-5A1 is also successfully textured using 10 vol. % BT templates, with a reported f(001) ~ 0.86. Both starting micron-sized matrix grains and the lack of PbO addition, result in no texturisation being attained. BT template grains are thermally unstable within the PZT matrix. Large grain growth is observed in samples sintered for up to 8 hours. Modification of the starting Zr:Ti ratio of the PZT matrix to ~ 56 Zr mol. % is carried out due to a shift in the morphotropic phase boundary (MPB) for the PZTx-5BT system. This results in an optimum tetragonal composition (Pb0.947(Ba0.053Zr0.531)Ti0.469O3) adjacent to the MPB, which exhibits piezoelectric properties (d33 ~ 450 pC/N, with Tc ~ 340 °C) to rival commercial PZT-5A1 (d33 ~ 410 pC/N, with Tc ~ 370 °C). In addition, there is evidence that the MPB curves towards the PbZrO3 (PZ) end member more sharply with respect to temperature than in the undoped PZT system, resulting in the appearance of Tr-t transitions in εr vs. temperature curves below Tc.