Dr. Wakako Araki

Study on materials for energy and environment from the mechanical point of view

 We have been working on the boundary between “solid mechanics” and “solid state ionics”. Solid mechanics is a study on mechanical behaviour of solid materials, whilst solid state ionics is a study on ionic behaviour in solid materials. We have been investigating both behaviours and the interaction between them in order to contribute to a safe and sustainable society from a mechanical standpoint.

Our current research interests focus mainly on materials for energy and environment, especially oxygen-ion conducting ceramics for high temperature use. Their typical application examples are solid oxide fuel cell (SOFC) and oxygen separation membrane for oxyfuel combustion process. We have been investigating ferroelastic/anelastic behaviour of these ceramics (Fig. 1) and also stress/strain effect on oxygen-ion mobility (Fig. 2). Further area of interest includes a development of non-destructive inspection of those devices by means of resonant ultrasound spectroscopy.

   Many of our current researches have been carried out in collaboration with Jülich Forschungszentrum, Germany. Also, some collaborative works were conducted with Imperial College London, UK.

  Figure 1  Ferroelasticity of lanthanum cobaltite: Strontium and iron-doped lanthanum cobaltite materials (LSCF) are a promising material for cathode of SOFC and also for oxygen separation membrane. Although LSCF is a good mixed oxygen-ion/electron conductor, it exhibits a quite unusual mechanical behaviour, known as ferroelasticity, due to its unique microstructure (observed as striped patterns). We have been investigating the mechanical behaviour of LSCF as well as its effect on the conductivity to ensure the safe usage of the ferroelastic materials and seeking for possible applications of this peculiar property.



  Figure 2  Oxygen-ion migration in yttria stabilised zirconia under mechanical stress: Yttria stabilized zircoina (YSZ) is a good oxygen-ion conductor and one of the most common electrolyte materials of SOFC. We have intensively investigated the mechanical stress/strain effect on oxygen-ion mobility. Our molecular dynamics simulation revealed that the oxygen-ion mobility can be enhanced by applying tensile stress. This result could lead to an improvement of power performance of SOFC and a development of novel electrolyte material. Our experimental work on this theme was awarded the best paper award of the year in a prestigious international journal (Solid State Ionics, 2011).



Figure 2 Movie (AVI 2.643KB)