R. Benedek, Argonne National Laboratory
K. Albe and R. S. Averback, University of Illinois, Urbana-Champaign
L. H. Yang, Lawrence Livermore National Laboratory
A. Alavi, Queen's University, Belfast

Research Objectives

This simulation project is part of an effort to characterize on an atomic scale the structure and physical properties of ceramic/metal interfaces; it complements the experimental program of Prof. D. N. Seidman. A primary focus of our work is the development of a realistic model potential suitable for molecular dynamics and Monte Carlo simulation of ceramic/metal interfaces, with misfit included.

Computational Approach

Most of our calculations are based on the plane wave pseudo-potential implementation of local density functional theory (LDFT). We apply first-principles LDFT calculations to generate a database that, in conjunction with experimental information, enables parameters for a realistic interface interatomic potential to be determined. When our model ceramic/metal interface potential is validated, this potential will be embedded in a multiscale (quasicontinuum) code to enable the simulation of mechanical properties.

Accomplishments

Calculations were performed of the layer-by-layer density of electronic states for coherent {222}MgO/Cu interfaces with three different parallel translations: (i) hollow site, (ii) bridge site, and (iii) on-top sites of the interface Cu layer relative to the terminating oxygen layer. The actual semicoherent interface may be viewed as a kind of composite with local regions that approximate each of these three high-symmetry configurations. The interface electronic states within the MgO gap are found shifted to higher energy for the on-top configuration relative to the hollow site, whereas a small density of states in the MgO gap are found for the bridge site configuration.

A classical modified embedded atom method (MEAM) interatomic potential has been developed for the well-studied model interface Nb/alumina. First-principles LDFT calculations were performed to generate a database for determining the potential parameters. To supplement those results, calculations of the equation of state have been performed for cubic NbO, rock salt NbAl, and rutile NbO₂.

	A MEAM potential for the Nb/alumina interface has been developed using input data from first-principles total-energy calculations. The figure shows energy-volume equations of states obtained by Birch-Murnaghan fits to LDFT calculations. Each curve represents a monatomic or binary system in a cubic structure. The thermomechanical properties derived for pure Al, pure Nb and Nb-O are in excellent agreement with experimental values. Results for the hypothetical structures (i.e., oxides with B1-structure), which do not occur experimentally, are also employed in the fitting procedure.

Significance

Ceramic-metal interfaces are prominent in many advanced materials, including high-temperature alloys, sensors, electronic components, and medical prostheses. But the simulation of properties of real ceramic/metal interfaces has been hampered by the lack of realistic interatomic potentials as well as the disparate length and time scales involved. Our aim is to start at the atomic scale and work towards continuum-length scales.

Publications

R. Benedek, D. N. Seidman, M. Minkoff, L. H. Yang, and A. Alavi, "Atomic and electronic structure and interatomic potentials at a polar ceramic/metal interface: {222}MgO/Cu," Phys. Rev. B 60, 16094 (1999).

D. A. Muller, D. A. Shashkov, R. Benedek, L. H. Yang, J. Silcox, and D. N. Seidman, "Atomic-scale studies of the electronic structure of ceramic/metal interfaces: {222}MgO/Cu," Materials Science Forum 99, 294 (1999).

D. A. Muller, D. A. Shashkov, R. Benedek, L. H. Yang, J. Silcox, and D. N. Seidman, "Atomic scale observations of metal-induced gap states at {222}MgO/Cu interfaces," Phys. Rev. Lett. 80, 4741 (1998).