Accession Number : ADA290879

Title :   Molecular Modeling of PMN Ceramics.

Descriptive Note : Final rept.,

Corporate Author : NAVAL UNDERSEA WARFARE CENTER NEWPORT DIV NEW LONDON CT NEW LONDON DETACHMENT

Personal Author(s) : Kavarnos, George J.

PDF Url : ADA290879

Report Date : 23 JAN 1995

Pagination or Media Count : 42

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)

Descriptors :   *MAGNESIUM, *CRYSTAL STRUCTURE, *MODELS, *MOLECULES, *CERAMIC MATERIALS, *LEAD COMPOUNDS, *NIOBATES, ANNEALING, STABILITY, INTERACTIONS, POLYMERS, CRYSTAL LATTICES, OBSERVATION, ELECTRIC FIELDS, CRYSTALLIZATION, ATOMS, FERMI SURFACES, PIEZOELECTRIC CRYSTALS, BONDING, LANTHANUM, ELECTROSTRICTION, ZIRCONATES, MOLECULAR ORBITALS.

Subject Categories : Ceramics, Refractories and Glass
      Inorganic Chemistry
      Physical Chemistry
      Atomic and Molecular Physics and Spectroscopy

Distribution Statement : APPROVED FOR PUBLIC RELEASE