Interaction between Ni/NiO and PbTiO₃: Phase reversal with redox switching

In some applications it is useful to have Pb(Zr,Ti)O₃ (PZT) films printed and fired on metallic substrates because of low cost, ease of handling, and mechanical flexibility of the substrate. As part of the systematic studies on phase compatibility of metallic substrates with PZT ceramics, studies have been conducted on the interaction between Ni and PbTiO₃ under oxidizing and neutral conditions at 1123 K. Phase relations in the pseudoternary system NiO-PbO-TiO₂ and quaternary Ni-Pb-NiTiO ₃-PbTiO₃ were explored by equilibrating compacted mixtures of component oxides and/or metals in air and prepurified Ar gas. The equilibrium phases were identified by x-ray diffraction and energy dispersive spectroscopy. The results suggest that NiO is phase compatible with PbTiO ₃. When nickel surface is oxidized, NiO is in direct contact with PbTiO₃ and there is no displacement reaction between NiO and PbTiO₃. However, in neutral and reducing conditions metallic Ni reacts with PbTiO₃ to form NiTiO₃ and a lead-rich alloy, with catastrophic consequences in device applications. The results are rationalized using a thermodynamic analysis. The nature of phase relations in the system Ni-Pb-Zr-O is elucidated using thermodynamic data.