Lanthanum silicate thin films for application as electrolyte of SOFCs

Milena M. Nogueira Vieira ,  João C. Oliveira ,  Alexander L. Shaula ,  Albano Cavaleiro ,  Bruno Trindade 

ICEMS - Mechanical Department, Faculty of Science and Technology Coimbra University (ICEMS-FCTUC), Pinhal de Marrocos, Coimbra 3030-201, Portugal

Abstract

Nowadays, Solid Oxide Fuel Cells (SOFCs) are seen as a future alternative energy generation source. The commercial SOFCs have been operated at 1000ºC to insure a sufficient ionic conductivity of their yttria-stabilized zirconia (YSZ) electrolyte. However, the high working temperature causes serious problems in terms of materials degradation and lifetime. There is therefore a lot of interest in develop new solid electrolyte materials for lower temperatures applications. Recently, apatite-type lanthanum silicates of general formula La10-x(SiO4)6O3-1,5x  have gained considerable attention because they exhibit high ionic conductivity and low activation energies at low temperatures besides they allow a wide range of substitutional possibilities [2, 3]. One key problem is the high processing temperature necessary to prepare them [4].

The aim of this contribution is the production of apatite-like lanthanum silicates thin films by magnetron sputtering. Thin films with the appropriate La/Si atomic ratios were deposited by reactive magnetron sputtering from LaSi and Si targets and subsequently annealed in controlled atmosphere to obtain the targeted lanthanum silicate oxide. The influence of the adding of germanium in the production of lanthanum germanosilicate thin films was also investigated.

The Chemical composition of the coatings was determined by electron probe analysis (EPMA). The structure was studied by X-ray diffraction (XRD) using a Phillips diffractometer operated in Bragg-Brentano configuration with Co (Ka) radiation. The cross section and surface topography of the La-Si films were examined on a JEOL scanning electron microscope (SEM) equipped with an EDAX energy dispersive spectrometer (EDS). The electrical properties of the films were measured by AC impedance spectroscopy (HP4284A precision LCR meter, 20 H z – 1 MHz).

[1] Fuel Cell Handbook, EG&C Pearsson, Inc., Science Applications International Corporation, U. S. Department of Energy, October 2000.

[2] H. Arikawa, H. Nishigushi, T. Ishihara and Y. Takita, Solid State Ionics, 136-137, 31-37, 2000.

[3] P. R. Slater, J. E. H. Sansom, J. R. Tolchard, The Chemical Record, 4, 373-384, 2004.

[4] S. Nakayama, M. Sakamoto, Journal of Materials Science Letters 20, 1627-1629, 2001.

 

Related papers
  1. Nanocomposite TM-dichalcogenides sputtered self-lubricating coatings alloyed with C

Presentation: Oral at E-MRS Fall Meeting 2009, Symposium G, by Milena M. Nogueira Vieira
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-11 11:50
Revised:   2009-06-07 00:48