Every year 1,000 trillion new pieces of multilayer ceramic capacitors enter the market inside the consumer, industrial and military products, and as their sizes shrink their microstructure features are projected to approach the nanomaterial scale within the next decade. This project will focus on BaTiO3, the ceramic material used in these capacitors, to determine the most important material parameters required to propel continued advances into the next generations. The project will also provide rich educational and research opportunities to engage students and educators in the Philadelphia area and in the larger community. In particular, the University of Puerto Rico-Humacao will benefit by gaining internet access to some measurement instruments in the Penn laboratory.
TECHNICAL DETAILS: This project will investigate nanograin BaTiO3 ceramics for possible dielectric, ferroelectric and piezoelectric applications. By varying the grain size, grain boundary charge and crystal stability of the nanograin ceramics, it will seek to engineer a tunable nanocomposite without apparent compositional inhomogeneity. The composite effect will rely on charge/defect-induced internal fields to smear structural transitions and clamp polarization, creating stable dielectrics with temperature-independent dielectric responses. Such possibility was not previously available in conventional ceramics because until the advent of nanomaterials, the width of the space charge zone has been much less than the grain size. The project will take advantage of a recent breakthrough in sintering technology that allows densification without grain growth, which avails nanograin BaTiO3 ceramics. Integrated research and educational activities built around laboratory discoveries will train new students in the field of nano electronic materials for future innovation and development.
, but how they manifest in the nano world, the world of a size from several tens to several hundreds of atoms in length, is less well understood. The goal of this project is to explore dielectric and related phenomena at such length scale (several to several tens of nanometers) using prototypical ferroelectrics, dielectrics, and metal-doped dielectrics in polycrystals, single crystals, and amorphous thin-film ceramics. The emphasis is on transitions of phases and physical properties, and on the role of internal and external fields caused by either electric or mechanical forces. We have succeeded in demonstrating the internal fields and field discontinuities at grain boundaries in polycrystals can smear and shift phase transitions and dielectric properties. We also demonstrated the electric conductivity is size dependent, and whether a film is conducting or insulating depends not only on composition, but also on the thickness and the voltage history. In many dielectrics doped with a small amount of metal atoms, they surprisingly behave like a metal when the film is a few nm thin. Moreover, when the film is capable of storing electric charge, the trapped charge can attract other charged species, especially water-associated ones, and cause rupture of atomic bonds, which can be mitigated by modifying the wetting properties of the dielectric surface. These results have elucidated the fundamentals of nanograin ceramics for dielectric, ferroelectric and piezoelectric applications, and identified causes and provided solutions for degradation of dielectrics. The project also trained two PhD—one already graduated—to become experts in the design, fabrication and characterization of ceramics, thin films and electronic devices. The project further provided research opportunities for one master student, and several undergraduates. Finally, this research has opened up new possibilities for electronic memory and ionic conductors, which are being investigated in new research projects funded by industry and other research entities.
