Margarita P. Thompson

Stress-induced polarization-graded ferroelectrics

Polarization-graded ferroelectrics and their electrically active embodiments, graded ferroelectric devices and transpacitors, have been formed from a variety of material systems, both by grading the composition of the ferroelectric and by imposing temperature gradients normal to the electrode surfaces. In this letter, we show how these same devices can be formed from homogeneous ferroelectric films of lead strontium titanate by imposing stress gradients on the material normal to their electrode surfaces.

Alloys that form conductive and passivating oxides for proton exchange membrane fuel cell bipolar plates

During the operation of proton exchange membrane (PEM) fuel cells, a high-resistance oxide is often formed on the cathode surface of base metal bipolar plates. Over time, this corrosion mechanism leads to a drop in fuel cell efficiency and potentially to complete failure. To address this problem, we have developed alloys capable of forming oxides that are both conductive and chemically stable under PEM fuel cell operating conditions. Five alloys of titanium with tantalum or niobium were investigated. The oxides were formed on the alloys by cyclic voltammetry in solutions mimicking the cathode- and anode-side environment of a PEM fuel cell. The oxides of all tested alloys had lower surface resistance than the oxide of pure titanium. We also investigated the chemical durability of Ti-Nb and Ti-Ta alloys in more concentrated solutions beyond those typically found in PEM fuel cells. The oxide films formed on Ti-Nb and Ti-Ta alloys remained conductive and chemically stable in these concentrated solutions. The stability of the oxide films was evaluated; Ti alloys having 3% Ta and Nb were identified as potential candidates for bipolar plate materials.

Enhanced pyroelectric sensitivity using ferroelectric active mode detection

Active pyroelectric detection (APD), using ferroelectrics as the sensing materials, is described and compared to traditional-passive pyroelectric modes of operation. The active approach yields a number of distinct advantages over its passive counterparts, including greater effective pyroelectric coefficient and improved signal to noise ratio. Thin film test structures formed from strontium bismuth tantalate (SrBi2Ta2O9) are used to demonstrate the APD principle.