Research Interests

Since joining UCSB, my research interests have been in two main areas: Electrical Properties of Ceramics; The Development of PiezoSpectroscopy and Its Applications to Materials.

Since it is difficult to limit new ideas when they arise, we have also tackled a number of basic questions in Materials. Recently, for instance, we have addressed the following:

• How to combine dislocation models for work hardening with continuum models?
• If a liquid is located at a grain boundary intercepting a free surface, under what conditions does the liquid wet the free surface and dewet the grain boundary, and vice versa?
• Is the hardness of a metal dependent on size?
• If one knows the properties of a set of individual grain boundaries, how can one deduce the overall, macroscopic properties of a polycrystalline material?

Electrical Ceramics

Within this subject of enormous scope and importance to Society, our work is concerned with three main issues:

1. how are the transport properties dependent on the electrical properties of their grain boundaries? (In particular in those ceramics, such as varistors and high-Tc superconducting ceramics, where the electrical properties are highly nonlinear)
2. how does electrical failure occur and how is it related to the microstructure? (In many ceramics failure occurs by the propagation of a hole through the material or by fracture)
3. the overall properties of composites of two or more phases each with their own distinct properties.

PiezoSpectroscopy

Broadly speaking, piezospectroscopy is concerned with the effect of strain on the spectroscopic properties of solids. In our work we primarily use a laser beam in an optical microscope to excite a spectral signal (fluorescence or Raman) from a region selected in the microscope. From the signal (its frequency shift and broadening) we determine the local stress and stress gradients.

The techniques are non-destructive and can be used to study the stress from regions just a few microns across. We have been using it to study a wide variety of materials phenomena, ranging from electromigration and residual stresses in microelectronic interconnects, to stresses in fiber composites, to addressing fundamental problems of stresses in ceramics. In the last year we have discovered that this technique is also applicable to stresses in oxide scales and has enabled us to begin to tackle fundamental issues, such as the reactive element effect and why compressive oxide scales spall, associated with oxidation of superalloys and the reliability of thermal barrier coatings.