2015/2/20 (金）

Structure-property relationship in piezoelectric materials

Piezoelectricity exists in varies types of materials such as solid ceramics, single crystals as well as biological matters, and these materials are extensively found in sensors, actuators and transducers for commercial, scientific and daily-life uses. One of the most popular family displaying piezoelectric properties belongs to the class of crystal structure called the perovskite, which has the basic chemical formula ABX3, where A and B are cations and X is an anion, usually oxygen. The fundamental structure is cubic, with the anions forming a corner-linked array of octahedra. The A cation occupies the space between the octahedra while the B cation is at the centre of the octahedra. Although the aristotype of this material is highly symmetrical, with temperature change, pressure change or chemical modification, it is easily distorted into a lower symmetry. The structural modifications are usually very subtle, but they have significant effects on the properties of the material. The structural phase transitions induced by temperature, pressure or chemical composition are believed to be highly related to the piezoelectric performance of the crystals and therefore become the core subject in both fundamental study to clarify the origin of some materials’ high property and the application study to manufacture devices ready to use in all kinds of environments. Among the large variety of the perovskites piezoelectric crystals, the solid solution of lead zirconate and lead tinanate (PbZr1-xTixO3, PZT) and the solid solution of lead magnesium niobate and lead tinanate ((1-x)[PbMg1/3Nb2/3O3]-x[PbTiO3], PMN-PT) have displayed the most excellent piezoelectric properties. It is commonly believed to be attributed to the formation of morphotropic phase boundary or region. Considering the toxicity of the large amount of lead used in both PZT and PMN-PT, there are also considerable efforts all over the world trying to find lead-free materials to replace PZT / PMN-PT in the near future. Success of the finding is based on the similarity of the lead-free candidates with the original high-performed peizoelectrics as well as the correct fundamental understanding of the general property-structure relationship from the material science point of view. In this talk, some fundamental knowledge of the crystal symmetry as well as the effects of the structural change on the materials’ property will be explained. Certain materials will be discussed as the examples of the experimental techniques and the analytical methods to study this subject. Finally, the future in the scientific and application aspects for piezoelectrics studies will be summarized in the hope of an inspiration for students especially the future scientists.

2013/8/19 (月)

When Society Changes Faster than Culture: Youth and the "Dark Side" of Globalization in Post-Industrial Japan

Dr. Vinai Norasakkunkit examines how Japanese youth are being marginalized in their own society by focusing on the psychological consequences of cultural practices at the institutional level, especially in the labor market, not keeping up with social structural changes and globalization trends. Specifically Dr. Norasakkunkit argues that Japanese youth bear the brunt of the cost of institutional resistance to globalization pressures. He further experimentally examines some of the psychological consequences of being marginalized in this way, including shifting values and shifting motivational processes. This research is the culmination of Dr. Norasakkunkit’s work in experimental cultural psychology and some theoretical work at the intersection of psychology and sociology. This research examines what is happening in postindustrial Japan as an example of some of the challenges related to social structural changes due to globalization pressures.

2012/6/19 (火）

Reversibility of Arctic sea ice retreat - a conceptual multi-scale modeling approach.

Arctic summer sea ice has retreated at increased rates over the past decade. Large modeling efforts are undertaken to predict the future of Arctic sea ice, since it profoundly influences the future of a warming climate and life on earth. Global circulation models (GCMs) are currently the primary tool used to project climate over the next century. However, the complexity of highly parameterized GCMs makes it very difficult to assess feedback processes in climate without the concurrent use of conceptual models. We have developed a lattice-type thermodynamic complex systems model for the ice-albedo feedback that includes the basic physics of ice-water phase transition, a nonlinear diffusive energy transport in a possibly heterogeneous ice-ocean layer, and spatiotemporal atmospheric and oceanic drives. We show that reversibility of Arctic sea ice retreat strongly depends on the albedo parameterization and on the spatial scale of the model.

2012/6/13 (水）

Climate, buildings and infrastructure

2012/2/28 (火）

The Variational Cluster Approximation

A main challenge in present solid state theory is the description of strongly correlated electron systems. Among the schemes proposed for the solution of this problem there are also variational principles for the electronic self-energy. In the present talk one of the schemes, the variational cluster approximation will be explained. This relies on the numerical generalization of trial self-energies by exact diagonalization of small clusters. As an application, the spin state transition in LaCoO_3 will be discussed.

2012/2/20 (月)

Reaction Rate and Solvation Dynamics in Neat Solvents, Electrolyte Solutions and Ionic Liquids:Similarity and Differences