Both oriented ordered NBCO films and oriented SDC films were successfully deposited on STO (001) substrates.
The initial aim when depositing the single layer films was also to compare the AC impedance of the single layer with the multilayer films, however instability in the NBCO material prevented this. As the NBCO was designed to be used as a cathode for IT-SOFCs, its instability in air and oxygen at 600°C shows that it is not fit for purpose. One of the hopes was that growing multilayers with SDC capping layers would improve the stability, however this was also unsuccessful.
Following on from this work multilayers of the SDC and NBCO films were also grown. A set of multilayer films were deposited with 2nm, 5nm, 10nm and 15nm of each layer.
One of the challenges of these multilayer films was that the NBCO required deposition at 850°C, whereas it was found that the SDC grew with a lower surface roughness at lower temperatures of around 650°C. Combining these films into the multilayer introduced the challenge of whether it was better to sacrifice some of the surface roughness of the SDC and use the higher temperature or not. From the TEM and EDX data there is likely migration of Nd into the SDC layers. The interfaces are also less sharp for the multilayer films deposited at the higher temperature for the SDC growth. However, in all cases the SDC growth appears more favourable in the TEM when compared to the NBCO, with some regions even showing Co-metal and fluorite structures potentially attributed to Co-Ox where we would expect to see the perovskite block.
As the NBCO was not stable enough to carry out reliable impedance measurements a second cathode material was chosen for further study and more information on this is discussed in Chapter 4. Further experiments could include replacing the NBCO in the multilayer film with another more stable perovskite structure to continue to investigate the relationship between the perovskite and fluorite interfaces.
3.7 References
1 Taskin, A. A., Lavrov, A. N. & Ando, Y. Transport and magnetic properties of GdBaCo2O5 single crystals: A cobalt oxide with square- lattice CoO2 planes over a wide range of electron and hole doping. Physical Review B71, 134414 (2005).
2 Burriel, M. et al. Anisotropic Oxygen Ion Diffusion in Layered PrBaCo2O5+δ. Chemistry of Materials 24, 613-621, doi:10.1021/cm203502s (2012).
3 Tarancon, A., Burriel, M., Santiso, J., Skinner, S. J. & Kilner, J. A. Advances in layered oxide cathodes for intermediate temperature solid oxide fuel cells. Journal of Materials Chemistry 20, 3799-3813, doi:10.1039/b922430k (2010).
4 Parfitt, D., Chroneos, A., Tarancon, A. & Kilner, J. A. Oxygen ion diffusion in cation ordered/disordered GdBaCo2O5+[delta]. Journal of Materials Chemistry21, 2183-2186, doi:10.1039/c0jm02924f (2011). 5 Taskin, A. A., Lavrov, A. N. & Ando, Y. Achieving fast oxygen diffusion
in perovskites by cation ordering. Applied Physics Letters 86, -, doi:doi:http://dx.doi.org/10.1063/1.1864244 (2005).
6 Kim, G. et al. Rapid oxygen ion diffusion and surface exchange kinetics in PrBaCo2O5+x with a perovskite related structure and ordered A cations. Journal of Materials Chemistry 17, 2500-2505, doi:10.1039/b618345j (2007).
7 Yuan, Z. et al. Epitaxial behavior and transport properties of PrBaCo2O5 thin films on (001) SrTiO3. Applied Physics Letters 90, -, doi:doi:http://dx.doi.org/10.1063/1.2741407 (2007).
8 Burriel, M. et al. Influence of the Microstructure on the High-Temperature Transport Properties of GdBaCo2O5.5+δ Epitaxial Films. Chemistry of Materials22, 5512-5520, doi:10.1021/cm101423z (2010).
9 Kim, G. et al. Oxygen exchange kinetics of epitaxial PrBaCo2O5+δ thin
films. Applied Physics Letters 88, -,
10 Grygiel, C. et al. A-Site Order Control in Mixed Conductor NdBaCo2O5+δ Films through Manipulation of Growth Kinetics. Chemistry of Materials 22, 1955-1957, doi:10.1021/cm9037022 (2010).
11 Frank, F. C. The influence of dislocations on crystal growth. Discussions of the Faraday Society5, 48-54, doi:10.1039/df9490500048 (1949). 12 Burton, W. K., Cabrera, N. & Frank, F. C. The Growth of Crystals and the
Equilibrium Structure of their Surfaces. Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 243, 299-358, doi:10.1098/rsta.1951.0006 (1951).
13 Bennema, P. Spiral growth and surface roughening: Developments since Burton, Cabrera and Frank. Journal of Crystal Growth 69, 182-197, doi:http://dx.doi.org/10.1016/0022-0248(84)90027-7 (1984).
14 Scheel, H. J. Materials Engineering Problems in Crystal Growth and Epitaxy of Cuprate Superconductors. MRS Bulletin 19, 26-32, doi:doi:10.1557/S0883769400047953 (1994).
15 Lobanovsky, L. S., Troyanchuk, I. O., Szymczak, H. & Prokhnenko, O. Structure and physical properties of layered double perovskite NdBaCo2O5.50 + δ (δ ≈ 0.25). J. Exp. Theor. Phys. 103, 740-746, doi:10.1134/s1063776106110094 (2006).
16 Pralong, V., Caignaert, V., Hebert, S., Maignan, A. & Raveau, B. Soft chemistry synthesis and characterizations of fully oxidized and reduced NdBaCo2O5+δ phases δ=0,1. Solid State Ionics 177, 1879-1881, doi:http://dx.doi.org/10.1016/j.ssi.2006.06.013 (2006).
17 Zachariasen, W. H. Zeitschrift fuer Physikalische Chemie123, 134 (1926). 18 B. E. Gushee, L. K., R. Ward. The preparation of a barium cobalt oxide and other phases with similar structures. Journal of the American Chemical Society79, 5601 (1957).
19 Roth, W. L. The magnetic structure of Co3O4. Journal of Physics and Chemistry of Solids25, 1 (1964).
21 Troyanchuk, I. O. et al. Magnetic and crystal structure phase transitions in R1-xBaxCoO3-y (R = Nd, Gd). Journal of Physics: Condensed Matter 12, 2485 (2000).
22 Garcia-Barriocanal, J. et al. Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO2:Y2O3/SrTiO3 Heterostructures. Science 321, 676-680 (2008).
23 Guo, X. Comment on “Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO2:Y2O3/SrTiO3 Heterostructures”. Science 324, 465, doi:10.1126/science.1168940 (2009).
24 García-Barriocanal, J. et al. Response to Comment on “Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO2:Y2O3/SrTiO3 Heterostructures”. Science324, 465, doi:10.1126/science.1169018 (2009). 25 Sanna, S. et al. Fabrication and Electrochemical Properties of Epitaxial
Samarium-Doped Ceria Films on SrTiO3-Buffered MgO Substrates. Advanced Functional Materials 19, 1713-1719, doi:10.1002/adfm.200801768 (2009).
26 M.M.J. Treacy, M.W. Deem & Newsam, J. M. DIFFaX. (http://www.public.asu.edu/~mtreacy/DIFFaX.html).
27 Windt, D. L. IMD—Software for modeling the optical properties of multilayer films. Computers in Physics 12, 360-370, doi:doi:http://dx.doi.org/10.1063/1.168689 (1998).
28 Geiersbach, U., Bergmann, A. & Westerholt, K. Preparation and structural properties of thin films and multilayers of the Heusler compounds Cu2MnAl, Co2MnSn, Co2MnSi and Co2MnGe. Thin Solid Films425, 225- 232, doi:http://dx.doi.org/10.1016/S0040-6090(02)01091-X (2003).
29 Zabel, H. Festkörperprobleme 30, Advanced solid state physics, X-ray and Neutron Scattering at Thin Films. (1990).
30 Laureti, S. et al. Effect of oxygen partial pressure on PLD cobalt oxide films. Applied Surface Science 254, 5111-5115, doi:http://dx.doi.org/10.1016/j.apsusc.2008.02.055 (2008).