Memorial University DAI: Brillouin scattering experiments near the a-B phase transition in single crystals of the N2 and CO

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Title	Brillouin scattering experiments near the a-B phase transition in single crystals of the N2 and CO
Author	Askarpour, Vahid
Description	Thesis (M.Sc.) -- Memorial University of Newfoundland, 1987. Physics
Date	1986
Pagination	x, 70, [9] leaves : photos, graphs
Subject	Brillouin scattering; Crystals--Spectra; Phase transformations (Statistical physics); Nitrogen--Spectra; Carbon monoxide--Spectra
Degree	M.Sc.
Degree Grantor	Memorial University of Newfoundland. Dept. of Physics
Discipline	Physics
Language	Eng
Notes	Bibliography: leaves [76]-[79]
Abstract	The technique of high resolution Brillouin spectroscopy has been used to determine the adiabatic elastic constants of large cooled single crystals of β-N2 and β-CO in an effort to gain insight into the α-β phase transition of these two unique examples of diatomic molecules which are extremely similar in many physical and chemical properties. The crystals were grown in a quartz cell inside a liquid helium cryostat. Laue x-ray diffraction analysis provided for the determination of the orientations of these crystals relative to the laboratory frame of reference. An argon ion laser beam was incident on the crystal and the scattered beam was analysed at 900 relative to the incident beam by a piezo-electrically scanned triple-pass Fabry-Perot interferometer. The signals were then collected by a photomultiplier tube, amplified through an amplifier/discriminator assembly and finally recorded by the data acquisition and stabilization system. - The values of elastic constants of β-N2 at 47.5 K in units of 109 N/m2 (subject to an absolute uncertainty of about 2%) are: c11-2.307 c12-1.454 c13-1.274 c33-2.488 c44-0.378. - The values of elastic constants of β-CO at 62 K in units of 109 N/m2 (subject to an absolute uncertainty of about 4%) are: c11-2.013 c12-1.212 c13-0.998 c33-2.227 c44-0.402. These values were compared to those at the corresponding triple points. There is an approximate elastic constant increase of 1% per 1 K of temperature decrease and there seems to be no evidence for mode softening in either N2 or CO. - Three large single crystals of β-CO were cooled slowly through the phase transition resulting in three single crystals of α-CO. The orientations of these face centered cubic crystals were determined and correlated to those of the hexagonal close packed phase. It was noted that the hexagonal basal planes appear to prefer to transform to planes of the form [110] of the cubic structure. A possible mechanism is discussed and the result is compared to previous works on metals and molecular crystals that undergo h.c.p. to f.c.c. phase transition.
Type	Text
Resource Type	Electronic thesis or dissertation
Format	Image/jpeg; Application/pdf
Source	Paper copy kept in the Centre for Newfoundland Studies, Memorial University Libraries
Local Identifier	75412535
Rights	The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.
Collection	Electronic Theses and Dissertations
Scanning Status	Completed
PDF File	(10.26 MB) -- http://collections.mun.ca/PDFs/theses/Askarpour_Vahid.pdf
CONTENTdm file name	331584.cpd