AVS 52nd International Symposium
    Advanced Surface Engineering Monday Sessions
       Session SE-MoA

Paper SE-MoA3
Alternating Covalent-Ionic and Metallic Bonding in Nanolaminated Cubic Perovskites

Monday, October 31, 2005, 2:40 pm, Room 201

Session: MAX Phases: Nanolaminates and Nanomechanical Measurements
Presenter: D. Music, RWTH Aachen, Germany
Authors: D. Music, RWTH Aachen, Germany
J.M. Schneider, RWTH Aachen, Germany
Correspondent: Click to Email
Using ab initio calculations, we have studied 35 cubic perovskites of RM@sub 3@X stoichiometry, where R and M are metals and X is a 2p nonmetal. In this structure (space group Pm-3m, prototype CaTiO@sub 3@), R atoms fill primitive cubic sites, M atoms are located at face centered cubic positions, and X is placed at body centered cubic Bravais nodes. We show that the coupling between M-R and M-X layers in RM@sub 3@X can be switched from predominantly covalent-ionic to metallic in character by varying the population of the M and R d-shells. As the X 2p population increases, the bulk modulus decreases, which can be understood by changes in bonding character from more covalent to more ionic due to splitting in density of states. We will also discuss transport properties obtained from phonon calculations. Based on the electron density distribution resemblance to the so-called MAX phases, it is reasonable to assume that alternating covalent-ionic and metallic bonding in these compounds may give rise to similar properties as observed for MAX phases.