| id |
ndltd-OhioLink-oai-etd.ohiolink.edu-osu1241098408
|
| record_format |
oai_dc
|
| spelling |
ndltd-OhioLink-oai-etd.ohiolink.edu-osu12410984082021-08-03T05:55:49Z Experimental determination of structure factors of TiAl and silicon Subramanian, Swaminathan <p>Brittleness of TiAl has been attributed to strong directional bonding by a number of researchers. Their predictions have been based on theoretical calculations of electron charge density distribution. It is necessary to complement these predictions by experimental measurements. The work described in this thesis, aimed towards that end, involves measurement of Debye-Waller factors by four circle x-ray diffraction and of structure factors by energy filtered convergent beam electron diffraction CBED methods.</p><p>Stoichiometric single crystals are required for the measurement of Debye-Waller factors by the four circle x-ray diffraction method. Because of constraints imposed by the phase diagram only non-stoichiometric single crystal of TiAl are available. Measurement of Debye-Waller parameters have been attempted by using aluminum rich TiAl single crystals of compositions Ti54at%Al and Ti56at%Al. The symmetry of L1<sub>0</sub> structure of TiAl dictates that all reflections with Miller indices (hkl) not satisfying the condition h+k=2n should be extinct. However, during the x-ray diffraction experiments diffuse diffracted intensities were observed for reflections of h+k=2n+1 type. This indicate the possibility of occupation of the excess A1 atoms on the Ti-sites. If the excess A1 atom preferentially occupies one of the Ti-sites, it would lead to the formation of Ll<sub>2</sub> type TiAl<sub>3</sub> unit cells within the TiAl lattice. This notion has been further verified by least-squares refinement of the data obtained from Ti54at%Al single crystal. Also Debye-Waller factor values were different for equivalent Ti-sites in TiAl.</p><p>The CBED method has been developed for accurate structure factor measurement. Factors such as limitation due to the angular resolution of the aperture and complex matrix and perturbation treatment of absorption have been considered. Computer routines, incorporating these factors, have been developed for the calculation of CBED patterns and for matching the rocking curves. The 220 structure factor of silicon has been measured, as a test case, to an accuracy < 0.1%. The temperature dependence of the coefficient of220 absorption potential has been determined. The results indicate the Einstein phonon model [Bird and King (1990)] underestimates the coefficient of 220 absorption potential of silicon.</p> 1994 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1241098408 http://rave.ohiolink.edu/etdc/view?acc_num=osu1241098408 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.
|
| collection |
NDLTD
|
| language |
English
|
| sources |
NDLTD
|
| author |
Subramanian, Swaminathan
|
| spellingShingle |
Subramanian, Swaminathan
Experimental determination of structure factors of TiAl and silicon
|
| author_facet |
Subramanian, Swaminathan
|
| author_sort |
Subramanian, Swaminathan
|
| title |
Experimental determination of structure factors of TiAl and silicon
|
| title_short |
Experimental determination of structure factors of TiAl and silicon
|
| title_full |
Experimental determination of structure factors of TiAl and silicon
|
| title_fullStr |
Experimental determination of structure factors of TiAl and silicon
|
| title_full_unstemmed |
Experimental determination of structure factors of TiAl and silicon
|
| title_sort |
experimental determination of structure factors of tial and silicon
|
| publisher |
The Ohio State University / OhioLINK
|
| publishDate |
1994
|
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1241098408
|
| work_keys_str_mv |
AT subramanianswaminathan experimentaldeterminationofstructurefactorsoftialandsilicon
|
| _version_ |
1719427957559132160
|
