Molecular Modeling of PMN Ceramics.
Abstract
Extended HOeckel theory was used to analyze the orbital interactions in PbNbO3(+) and LaNbO3(2+) model structures representative of lead magnesium niobate (PMN )ceramic. These structures were chosen to determine the orbital effects, if any, that an A-site substitutional such as Pb(2+) has on bond stability in the crystal lattice structure. It was determined that the A-site ion does not directly influence bonding between the A-site ion and atoms in the neighboring crystal lattice but does change the position of the Fermi level, which in PbNbO3(1+) is -10.1 eV and in LaNbO3(2+) is -14.5eV. In PbNbO3(+), the Fermi level is so positioned that the bonds linking Nb and O are destabilized. In contrast, there is no antibonding character in LaNbO3(+). The shifting of the Fermi level as a function of the A-site ion is used to rationalize the experimental observation that pure PMN does not coarsen or undergo additional crystallization during annealing, but La-substituted PMN does in fact favor ordering of the crystal structure. (jg)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 23, 1995
- Accession Number
- ADA290879
Entities
People
- George J. Kavarnos
Organizations
- Naval Undersea Warfare Center