SEu.., DRG 853 SUMMARY ABSTRACT: ANALYSIS OF CHEMICAL BONDING IN TIC I/i V

Transcription

1 5 DRG 853 SUMMARY ABSTRACT: ANALYSIS OF CHEMICAL BONDING IN TIC I/i V TIN AND TIO USING S. (U) CALIFORNIA UNIV LOS ANGELES DEPT OF CHEMISTRY AND BIOCHEMISTR.. S KIM ET AL. UNCLASSIFIED SEu.., 28 FEB 96 TR-iB N K-86i2 F/G 28/8 NL

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3 OFFICE CF NAVAL RESEARCH 10 Research Contract N K (, TRCHNICAL REPORT No. 10 I SUMMARY ABSTRACT: ANALYSIS CF CHEMICAL BONDING IN TiC, TiN, AND TiO USING SBCOND-PRINCIPLES BAND STWCTURES FROM PHOYEM1ISSION DATA by Sehun Kim and R. Stanley WilliamTs Published LE'CTE D J.Vac.Sci.Technol. Nov Department of Chemistry and Biochemistry University of California, Los Angeles, CA C1. C) LL- 0-i February, 1986 Reproduction in whole or part is permitted for any purpose of the United States Government. This document has been approved for public release and sale; its distribution is unlimited. 86

4 [.---.r. TJ ASS IF IED *"1::" SEcURITY CLASSIFICATION OF THIS PAGE M1on Data Entered) REPORT READ INSTRUCTIONS BAND SOCUMENTTIO PAGE BEFORE COMPLETING FORM 7. REPORT NUMBER 1n 0 12 GOVT ACCESSION NO. -,./ ; RECIIENT'$ CATALOG NUMBER Sehuri Kim and R. Stanlev y Wilam SUMMAR%"~~~13 ABSTRACT OPCAGIESBD. N K-0612 OFLYI 9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT. TASK( -. -, Department of Chemistry & BicherniistrvAEAIORCUTNUER U C L A - Los Angeles, CA If. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE *.., ChEnistry Program office 2 eray18 Office of Naval Research, Arlington, VA I Te 1R R Po 14 MONITORING AGENCY NAME S ADDRESS(II different tran Controlling Ofice) IS. SECURITY CLASS. (of this report) UNC!LASS IF TED I5a, DECLASSIFICATION SCHEDULE DOWNGRADING 16 DISTRIBUTION STATEMENT (of this Report) Approved for public release; distribution unlimtrited 17. DISTRIuUTION STATEMENT (of the abstract entered in M ock 20. It different from Report) 5 SUPPLEMENTARY NOTES -w-u Published '.-,UNCLASSIVFD in J.Matls.Sci.Soc. (1986), - I. K WORDS.EY (Continue o rver#* n *aid It necs e sary and Identify by block nuotb.r) chemical bonding - second-principles band structures photoemission electron densities - Pseudoptential calculations S-. 2b ABSTRACT (Continue an revrs~e old. It nece~ibary and identify by block numnber) -This investigation was -,tivated in pc~rt by the observation that the empirical seudorpotential calculations of the TiC electronic structure produced valence electron densities that disagree severely with those obtained from first-principles calculations. The intent of this study was to see if the mixed-basis band structure interpolation schnk (MBBSIS) could be used to obtain reliable band structures and charge densities for motre complex systemt, such as Ti-C, TiN, and Ti% * 4DD IOR 1473 EDITION OF I MV 6S S OSOLETE I2ASVE S 'N LF SECURITY CLASSIFICATION OF THIS PAGE (ften Vete Entered)

5 "> ", FILE: JVS I QUEUE:JVST-JVS o IS: pasteup FMT: jv tl BY: DEBBY,04/11,18:38 REV: DEBBY,06/11,15:18 08-NOV-85 21:45: JVS Running Tide: Summary Abstract Analysis of chemical bonding Summary Abstract: Analysis of chemical bonding in TIC, TIN, and TiO using second-principles band structures from photoemission data Sehun Kim and R. Stanley Williams - -.Department ofc/,em,ry and Biochemistry. University of California. Los Angeles. California 9X(24 (Received 16 September 1985; accepted 30 September 1985 ", This investigation was motivated in part by the observation 2 that the empirical pseudopotential calculations' of the TiC electronic structure produced valence electron densities that disagree severely with those obtained from first-principles Acknowledgmenut This work was supported by the Office calculations. 2 The intent of this study was to see ifthe mixed- of Naval Research. One of us (RSW) acknowledges the Cabasis band structure interpolation scheme (MBBSIS) ' could mille and Henry Dreyfus Foundation and the Alfred P. be used to obtain reliable band structures and charge densi- Sloan Foundation for financial support. We are grateful to.-'4 ties for more complex systems, such as TiC, TiN, and TiO. D. J. Chadi for enlightening discussions. Our method of calculation has been described in detail elsewhere. 4 The electron density associated with each band state was defined as the square of its MBBSIS eigenfunction, '. F. Alward. C. Y. Font, M. El-Batasouny. ad F. Wooten. Solid State which is a combination of 39 orthogonalized plane waves Coninun. Ii, , 2 Saf i P. Blahe and K. Schwartz. tat. J Quantum Chem ; _OPWI and Sd-wave functions in the present scheme. 'R.L aenbw * In a recent study, detailed d N. V. SnuB 27, band mapping was performed "S. Kit and R. S Willams 3144 (1983 he ublis m using angle-resolved photoelectron spectroscopy (ARPES) 'A. Callenas. L. I Jobanuon. A N Chistensen. K Schwartz. and J Re. Rao to obtain band dispersions for TiC 5 and TiN. 4 Noticeable dinger. Phys. RevB (19931 discrepancies between the first-principles results 5 6 and 'L I Jobansson. A Callenas. P M Stefan, A N Chnstensen, and K ARPES data 56 can be found. In particular, the experimental Schwartz, Phys Rey. B 24. 1t83 (1981 bands have a clear gand gap in the valence bands that does not appear in the calculations. 6 The MBBSIS energy bands FIG I Comparison of contour N " Ti : were empirically adjusted for TiC and TiN, and agree very plots between lal the total charge La well with the ARPES data. 5 ' 6 density of the bands fitted to the first-princtples results of Ref 6 The total valence electron densities of TiC, TiN, and TiO and tbl that of the empirically adcalculated by the MBBSIS fitted to the first-principles re- justed bands for TiN. normalized suits agree very well with the densities calculated in Ref. 2. to 9 electrons per unit cell The The electron densities around the nonmetal atoms are projection shown is a (loo plane spherically symmetric and show increased localization go- bounded by two Ti and N atoms ri I N "" ' ing from TIC to TiO. The electron densities around the titanium atom strongly deviate from spherical symmetry, and the N. :. Ti '+". imav deviation changes from e. symmetry for TiC to t 28 symmetry for be TiO. illustrated The relationship by examining between states banding with k and points bonding along (b) the A direction. The electron density plots for the first band with A, symmetry for the three Ti compounds illustrate the.. covalent bonding (pd,) between nonmetal 2p and Ti r,, or- '" N_ bitals. The electron densities around the Ti atom are reduced -.- "" going from TiC to TiO, while those around the nonmetal atoms increase. This indicates that TiC exhibits the highest., Vt degree of covalent bonding and that the more ionic character increases as the series progresses from TiC to TaO. Similar features are also found in the electron densities of the second " ". band of A, symmetry. The covalent bonding (pd.) character Accesion For %. between the nonmetal 2p and Ti e, orbitals is decreased going from TiC to TiO. The electron density plot for the band NTIS CRA&I ofa symmetry shows metal-metal (dd,) bonding. Most of 'C TAB electron density is piled up around the Ti atoms and the U.IouAced minimum electron densities are found around nonmetal U o atoms Figure I presents both lal the total charge density of JJbtificatlor Sshows,,~her the bands fitted to the first-principles results and (b) that of the emptrically adjusted bands for TN The latter pii electron density at th and a lower By 1"elctroensity at the Ti atom than the f6rmer. In TIC. con- N- trary to the TiN result, the corresponding plot of the semiempincal charge density shows a higher concentration at the Ti atom and a lower electron density at the C atom than those of the first-principles results. This means that the semiempncal band structures indicate more covalent bonding Dit character in TiC and more omic in TiN than the first-pnnci- * - plea resulta indicate In summary, the contribution ofcovalent. ionic, and metallic bonding in the three Ti compounds may be visualized.in the charge densities calculated by the MBBSIS. -o,*.... Di-t ibu tion Availability Codes Avail a:id / r spt _ial

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