DISCERNING INTERFACE ATOMISTIC STRUCTURE BY PHASE CONTRAST IN STEM

The stability of metal films on oxide surfaces is important for the performance of devices such as solid oxide fuel cells (SOFCs) and thermal barrier coatings (TBCs) [1, 2, 3]. Ni-YSZ serves as an anode material in SOFCs. During SOFC operation, the metal-ceramic interface is subjected to high temperatures and a reducing atmosphere, which can lead to coarsening of the Ni nanoparticles, which decreases the number of three-phase boundaries. The three-phase boundaries (Ni/YSZ/fuel-gas) are essential for catalytic activity which controls the electrical properties. A better understanding of the equilibrated Ni-YSZ interfacial structure and energy can lead to improved adhesion and long-term stability of SOFCs [4, 5].

In this work, solid-state dewetting of continuous Ni films deposited on the (111) surface of yttrium stabilized zirconia (YSZ) was used to produce equilibrated Ni particles, and after determination of the solid-solid interface energy [6], the structure of the same interface was determined using aberration corrected transmission electron microscopy. The ~150nm thick Ni films were annealed at 1350˚C (0.94 T_m) in Ar+H₂ (99.9999%) at a partial pressure of oxygen of 10^-20 atm for 6 hours. Transmission electron microscopy of equilibrated particles which was conducted to analyze the structure at the interface revealed that despite the 31% lattice mismatch between Ni and YSZ, the interface is semi-coherent and a two dimensional network of misfit dislocations was identified [7].

References:

1. R. M. Ormerod, Solid oxide fuel cells, Chemical Society Reviews, 32[1]:17-28, (2003).
   
   
2. A. B. Stambouli, E. Traversa, Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy, Renewable and Sustainable Energy Reviews, 6[5]:433-455, (2002).
   
   
3. A. Christensen, E. A. Carter, Adhesion of ultrathin ZrO2(111) films
   on Ni(111) from first principles, The Journal of Chemical Physics, 114[13]:5816-5831, (2001).
   
   
4. A. Tsoga, A. Naoumidis, P. Nikolopoulos, Wettability and interfacial reactions in the systems Ni/YSZ and Ni/Ti-TiO2/YSZ, Acta Materialia, 44[9]:3679-3692, (1996).
   
   
5. N. F. P. Ribeiro, M. M. V. M. Souza, O. R. M. Neto, S. M. R. Vasconcelos, M. Schmal, Investigating the microstructure and catalytic properties of Ni/YSZ cermets as anodes for SOFC applications, Applied Catalysis A: General, 353[2]:305-309, (2009).
   
   
6. H. Nahor, H. Meltzman, and W. Kaplan, "Ni–YSZ(111) solid–solid interfacial energy," Journal of Materials Science 1-8 (2013).
   
   
7. H. Nahor, W. D. Kaplan, Structure of the Equilibrated Ni(111)-YSZ(111) Solid-Solid Interface, submitted to The Journal of the American Ceramic Society (2015)