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Electron Density Determination and Bonding in Tetragonal Binary Intermetallics by Convergent Beam Electron Diffraction

Sang, Xiahan (2012) Electron Density Determination and Bonding in Tetragonal Binary Intermetallics by Convergent Beam Electron Diffraction. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Intermetallics offer unique property combinations often superior to those of more conventional solid solution alloys of identical composition. Understanding of bonding in intermetallics would greatly accelerate development of intermetallics for advanced and high performance engineering applications. Tetragonal intermetallics L10 ordered TiAl, FePd and FePt are used as model systems to experimentally measure their electron densities using quantitative convergent beam electron diffraction (QCBED) method and then compare details of the 3d-4d (FePd) and 3d-5d (FePt) electron interactions to elucidate their role on properties of the respective ferromagnetic L10-ordered intermetallics FePd and FePt.
A new multi-beam off-zone axis condition QCBED method has been developed to increase sensitivity of CBED patterns to change of structure factors and the anisotropic Debye-Waller (DW) factors. Unprecedented accuracy and precision in structure and DW factor measurements has been achieved by acquiring CBED patterns using beam-sample geometry that ensures strong dynamical interaction between the fast electrons and the periodic potential in the crystalline samples. This experimental method has been successfully applied to diamond cubic Si, and chemically ordered B2 cubic NiAl, tetragonal L10 ordered TiAl and FePd. The accurate and precise experimental DW and structure factors for L10 TiAl and FePd allow direct evaluation of computer calculations using the current state of the art density functional theory (DFT) based electron structure modeling. The experimental electron density difference map of L10 TiAl shows that the DFT calculations describe bonding to a sufficient accuracy for s- and p- electrons interaction, e. g., the Al-layer. However, it indicate significant quantitative differences to the experimental measurements for the 3d-3d interactions of the Ti atoms, e.g. in the Ti layers. The DFT calculations for L10 FePd also show that the current DFT approximations insufficiently describe the interaction between Fe-Fe (3d-3d), Fe-Pd (3d-4d) and Pd-Pd (4d-4d) electrons, which indicates the necessity to evaluate applicability of different DFT approximations, and also provides experimental data for the development of new DFT approximation that better describes transition metal based intermetallic systems.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Sang, Xiahanxis20@pitt.eduXIS20
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairWiezorek, Jörgwiezorek@pitt.eduWIEZOREK
Committee MemberBarnard, Johnjbarnard@pitt.eduJBARNARD
Committee MemberLee, Jung-kunjul37@pitt.eduJUL37
Committee MemberShankar, Raviravishm@pitt.eduRAVISHM
Date: 26 September 2012
Date Type: Publication
Defense Date: 14 May 2012
Approval Date: 26 September 2012
Submission Date: 29 May 2012
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 193
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Materials Science and Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: convergent beam electron diffraction, bonding, electron density, intermetallics, multi-beam off-zone axis condition, Debye Waller factors, structure factors
Date Deposited: 26 Sep 2012 17:13
Last Modified: 15 Nov 2016 13:58


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