Abstract

In the last two years, the US Naval Research Laboratory has been studying the potential of ferroelectric glass-ceramics for high energy density capacitor applications.   By nucleating and growing ferroelectric particulates in a porosity-free glass matrix, this approach yielded materials with ultra-high dielectric breakdown strength (up to 800 kV/cm), and dielectric constant as high as 1200.   In our study, glasses with network former (Si, Al, and B) content as low as 20 wt% were successfully formed by splash quenching.   By carefully selecting the modifiers/additives, we were able to control the formation of the desired ferroelectric phase (barium strontium titanate, BST) during crystallization.   Unfortunately, the energy density of the BST-based glass-ceramics was only ~1 joule/cc when measured using a discharge measurement circuit.   Polarization-electric field measurements revealed wide open hysteresis loops, indicating that most of the electrical energy was not released during discharge.   Subsequent experiments showed that the buildup of interfacial polarization was the likely cause in this composite dielectric system.   By establishing an equivalent circuit model, we quantified the dielectric response and explained the observed hysteretic behavior.   The results have important implications on the utilization of composite dielectrics in pulsed power applications.

Biography

 

Dr. Ming-Jen Pan is the Head of the Ceramics and Rapid Prototyping Section in the Multifunctional Materials Branch of the U.S. Naval Research Laboratory. He received the Ph.D. degree in Engineering Mechanics from The Pennsylvania State University in 1994. From 1995 to 1998, he worked as a Post Doctoral Scholar and later a Research Associate at Penn State. Between 1998 and 2001, Dr. Pan was a staff scientist at TRS Ceramics, Inc. (State College, PA) developing new dielectric and piezoelectric materials, prior to joining NRL in August 2001. His primary research interests include high energy density dielectrics, characterization of dielectric materials, formulation of piezoelectric materials, multilayer capacitors/actuators, and the fatigue behavior of piezoelectric single crystals.   In recent years, he extended his research into new areas such as acoustic landmine detection and energy mitigation materials for blast protection.