Ferroic Materials and Multiscale Phenomena

　　A huge class of materials exhibits spontaneous (automatic) order with respect to atomic/ionic displacement or spin below a characteristic temperature (Currie temperature); they are called ferroic materials. Such ordering transitions (called ferroic transition) result in very interesting phenomena at three different length scales simultaneously, from atomic/nano scale (atomic/ionic displacement, spin, etc.), mesoscopic scale (domain), to macroscopic scale (strain, electric effects, magnetic effects). The ferroic transitions and the associated multiscale phenomena, as typical examples of cooperative and self-organization phenomena, are not only of significant scientific interest but also of profound technological importance. Typical examples of important properties of ferroic materials include, but not restricted to, shape memory effect, superelasticity, pyroelectric effect, piezoelectric effect, huge mechanical, electrical and magnetic susceptibility, permanent magnetism and magnetostriction. Ferroic materials play an indispensable role in our modern society as major functional materials, and are expected to gain their importance in our electronic and information age in which conversion of different forms of energy (mechanical, electrical, magnetic, etc) is crucial.

A highly interdisciplinary research field

　　Traditionally, different kinds of ferroic materials (see classification of ferroic materials) were the subjects for different scientific communities. Metallurgists studied ferroelastic/martensitic alloys; ceramicists studied ferroelectric materials, whereas physicists studied ferromagnetic and superconductive materials. However, in recent years it has been gradually realized that fundamental physics in these apparently different groups of material bears striking similarity or analogy, and knowledge obtained in one group of materials can be applied to understanding parallel physical phenomena in other groups. Therefore, it is important to study different groups of ferroic material by an interdisciplinary approach.

Classification of Ferroic Materials

1、Ferroelastic/martensitic materials
multiscale phenomena: atomic displacement, domain, shape change, shape memory, superelasticity, high damping capacity, etc.

2. Ferroelectric materials
multiscale phenomena: ionic displacement/polarization, ferroelectric domain, electric charge, pyroelectricity, etc.

3. Ferromagnetic materials
multiscale phenomena: spin alignment, magnetic domain, magnetism, etc.

4. Hybrid ferroic materials (Ferroelasto-ferroelectric materials, ferroelasto-ferromagnetic materials, etc. …)
Many ferroic materials belong to this group and they are characterized by coupling among strain, electric polarization and magnetism. Such coupling can result in very interesting multiple response in strain, electric charge and magnetism, and are important for actuator and energy converter applications. Typical examples are piezoelectric effect, magnetostriction, and so on.

5. Non-conventional ferroic materials (HTc superconductors, some BCS superconductors, giant magnetoresistive materials)
In these materials, the interplay among dynamic strain (phonon), magnetism, and electrons plays an essential role in the abnormal physical properties. Such interaction is also an important topic in modern condensed matter physics.

Aim of Our Program

1. Explore physics of ferroic transition and associated multiscale phenomena by an interdisciplinary approach.

2. Explore and discover novel properties in ferroic materials and help to develop new functional materials.

Current Research Topics

Ferroelastic/martensitic materials

1. Strain glass in ferroelastic materials

2. Interaction of point defects with ferroelastic/martensitic transition and the associated exotic multiscale phenomena.

3. Point defects in ferroelastic/martensitic materials and atomic/ionic migration.

4. Precursor phenomena prior to ferroelastic/martensitic transition and their relation to the mechanism of the transition

5. Ti-Ni Shape memory alloys and aging effect

Ferroelectric materials

1. Non-lead piezoelectric materials

2. Possible exotic multiscale phenomena in ferroelectric materials, effect of point defect, aging effect, possible colossal piezoelectric effect and unusual memory effect.

3. doping mechanism and the role of point defects.

Computer simulation

Monte Carlo, Molecular dynamics simulations and theoretical modeling of multiscale phenomena in ferroic materials and effect of point defects.

Defect chemistry and measurement of point defect concentrations.

Varistor ceramics

1. ZnO Varistor ceramics

2. SrTiO3 Varistor ceramics

3. TiO2 Varistor ceramics