THEORETICAL STUDIES OF DEFECTS IN BINARY AND TERNARY ...

CONF-861207—62 DE87 004704

Theoretical Studies of Defects in Binary and Ternary Oxides*

W. Y. Ching,** D. E. Ellis,t and D. J. **Physics Department University of Missouri-Kansas City, Kansas City, MO * Physics Department Northwestern University, Evanston, IL 60201 I'Materials Science Division Argonne National Laboratory, Argonne, IL 60439 Tho submitted manuscript has boon nuthorcd bv a contractor of tho U. S. Govornmont under contract No. W-31-109-ENG-38. Accordingly, tho U. S. Government rotams a nonexclusive, roynlty*free ticonso to publish or roproduco tho published lorm ol this contribution, or allow others to do so, for U. S. Government purposes.

DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

*Work supported by the U.S. Department of Energy, Basic Energy SciencesMaterials Science, under contract W-31-109-Eng-38. Manuscript submitted to the Materials Research Society Annual Meeting, Boston, MA, December 1-2, 1986.

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THEORETICAL STUDIES OF DEFECTS IN BINARY AND TERNARY OXIDES* W. Y. CHING,** D. E. ELLIS,1" AND D. J. LAM1"1" **Physics Department University of Missouri-Kansas City, Kansas City, MO t'Physics x Department Northwestern University, Evans ton, IL 60201 'Materials Science Division Argonne National Laboratory, Argonne, IL 60439

INTRODUCTION In the past decade, there has been an explosive development of compu- —I tational techniques utilizing high-speed computers to study the electronic and atomic structural properties of solids. These techniques form an important compliment to laboratory experiments for providing a better — understanding of spectroscopic properties, as well as the energetics of the — solid systems. For ideal metallic and semiconducting crystal lattice with — translaticnal symmetry, the conventional energy band structure approaches — are capable to provide a good degree of precision in both electronic -• — structure and system energies. On the other hand the molecular-cluster — model represents a convenient method of studying those properties that are —t primarily a function of the local environment of the system, such as -i vacancy, substitutional and interstitial defects.

j In this paper, we will present some preliminary results of electronic structure of substitutional defects and vacancy in binary and ternary cubic •j zirconium oxides obtained by the embedded molecular-cluster model calculation. The importance of electronic charge redistribution in the solids where the defect is introduced into the perfect lattice will be highlighted and the effect of electron polarization of the surrounding ions of the defect will be discussed.

THEORETICAL APPROACH A complete discussion of the X discrete variational embedded cluster method, based upon the self-consistent local density formalism, has been presented in previous works [1-4]. Only a brief review will be given here. The ground state electronic structure of ideal and defected clusters were obtained using the self-consistent discrete variational method. At the beginning of a self-consistent iteration, charge density for appropriate cations and anions are summed to form crystal densities. Coulomb and exchange potentials are evaluated as would be required for an ordinary band-structure calculation. In the case of vacancy, we introduced a virtual atom with electron wavefunctions but no potential at the vacancy site of the lattice. Cluster wavefunctions and energies are next found by variational solution of the Schrodinger (or Dlrac-Slater for the relativistic code) equation, using a basis set constructed from numerical freeatom or ion wavefunctions. The cluster eigenstates are populated

*Work supported by the U.S. Department of Energy, Basic Energy Sciencesj Materials Science, under contract W-31-109-Eng-38.

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