Advanced electro-ceramics: role of nanoscience

Electro-ceramics have immense technological applications in energy conversion devices such as Fuel Cells, Oxygen storage capacitors and Li ion batteries etc. There is a growing need to develop better soft chemical synthesis routes as the conventional solid state method has several limitations. Among the available chemical routes, the combustion technique is capable of producing the nanocrystalline powders of the oxide ceramics at lower calcination temperature. This process involves a combustion reaction between a fuel (e.g. glycine, citric acid, urea etc.) and an oxidizer (e.g. metal nitrates). In my group, a wide range of materials for SOFC applications have been synthesized, such as ceria, Gd or Sm doped ceria, Zr0.8Ce0.2O2, YSZ, CeO2-Y2O3 solid solution, La1-xMxCrO3 (M = Ca, Sr), Sr-doped LaCoO3 and doped LaGaO3 etc. The powder properties were tailored to achieve near theoretical density sintered pellets. A number of techniques like XRD, HT-XRD, surface area analyzer, SEM, TEM, sinterability, Raman spectroscopy, dynamic light scattering, small angle X-ray/neutron scattering, dilatometer, AC Impedance analyzer etc. were used for detailed characterization of these products. A major emphasis was on the optimization of the processing parameters so as to get a highly sinteractive phase pure materials. The size and nature of agglomeration was found to be a crucial parameter affecting the sinterability. Another key issue of SOFC technology is the design of better ionic conductors. It is well known that ionic conductivity is a highly structure-driven property. Several new ionic conductors, such Nd3GaO6 and Nd2-xGd2Zr2O7 and Ba2In2-xTixO5+x/2 were prepared based on the structure-property correlation. Detailed XRD and Raman spectroscopy studies revealed that an optimum degree of disorder enhances the ionic conductivity. As an offshoot, this work resulted in preparation of interesting potential oxygen storage materials such as Gd2-xCexZr2O7 (x = 0.0 to 2.0) and Ce0.5Sc0.5O1.75 etc. These results will also be discussed. (author)