Decomposition of the ZrO₂electrolyte in contact with Ni: Structure and chemical composition of the Ni–electrolyte interface

The Ni/(ZrO₂+ 9.5 mol% Y₂O₃) interface was used as a model system to investigate decomposition reactions of a yttria-stabilized ZrO₂electrolyte in contact with a metal at elevated temperature. In the present study, the sample was a diffusion-bonded symmetrical galvanic cell Ni‌ZrO₂+ 9.5 mol% Y₂O₃‌Ni. Various electron microscopy techniques were used to study the morphology and structure of the reaction products at the Ni–ZrO₂electrolyte phase boundary after current flow. Below a critical oxygen partial pressure of approximately 10⁻²⁷atm, an intermetallic reaction layer formed at the Ni–electrolyte interface. Between the intermetallic layer and electrolyte a thin Y₂O₃layer was present, which acted as a diffusion barrier for Zr and Ni, slowing down the overall chemical reaction. At several locations at the interface the Y₂O₃layer broke up, leading to a morphological instability of the interface between electrolyte and Ni₅Zr, allowing further reaction. The thickness of the total reaction layer varied widely as a consequence of such an instability.