FRG: Unit Defect and Microstructural Processes at Metal/Dielectric Interfaces: An Integrated Experimental and Simulation Approach

NON-TECHNICAL DESCRIPTION: Lead-based dielectric materials continue to be the used in many electronic devices for communication, sonar, non-volatile memory, and echography, despite the fact that lead is environmentally and biologically incompatible. One common metal used in these devices is platinum because it conducts electrical current well and is resistant to oxidation and high temperatures. At high temperatures it is common for mixing to occur at the interface between the lead-based materials and the platinum, which ultimately limits the properties and performance of the devices. This project is focused on understanding these effects in platinum-lead-based dielectric interfaces and using this information to produce structures with improved electrical performance. The project concurrently trains the next generation of scientists, including graduate students, undergraduate students, and high school students, in state-of-the-art experimental and computational materials science and engineering. The training of underrepresented undergraduate students and outreach to high school students through summer research projects are also a focus of this activity.

TECHNICAL DETAILS: Lead-based perovskites, most prominently lead titanate and its derivatives, continue to be the dominant dielectric material for many applications despite the fact that lead is environmentally and biologically incompatible. One common metal electrode used in these devices is platinum because it is an excellent conductor and exhibits high oxidation and heat resistance. During high-temperature processing, the constitutive elements in these materials interdiffuse across the interface, controlling the development of crystallographic texture and composition and thereby defining the subsequent properties and performance characteristics. This project is focused on understanding the fundamental mechanisms at play at the metal-dielectric interface and using this mechanistic information to synthesize materials and heterostructures with controlled interfaces with improved electrical properties. A combination of experimental and computational methods is used to determine the mechanisms by which (i) lead diffuses into and out of lead titanate, and (ii) temperature-driven grain-boundary migration and texture evolution occurs at the platinum/lead titanate interface. The computational approaches include electronic structure calculations using density functional theory and atomic-scale molecular dynamics simulations. As part of the latter effort, new charge-optimized, many-body reactive potentials are being developed and disseminated to the computational community as part of the open-source LAMMPS software (http://lammps.sandia.gov/). Experimentally, phase and texture evolution during high-temperature processing are characterized using in situ diffraction techniques and diffusion across the interface is examined via quantitative electron microscopy. In addition, broadband impedance and electrical measurements are being used to determine the influence of structure on dielectric and ferroelectric behavior. The project is training the next generation of scientists in state-of-the-art experimental and computational materials science and engineering. Summer research projects will engage underrepresented undergraduate and high school students.