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|Title:||Elastic Constants of Plastic Crystals by Schaefer-Bergmann Scattering: Crystalline Cyclohexane and Deuteromethane|
|Author(s):||Marx, Steven Vincent|
|Department / Program:||Physics|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Condensed Matter|
|Abstract:||The Schaefer-Bergmann technique for sound velocity measurement has been adapted for use with solidified liquids and gases. The advantages of this method for measuring elastic constants of plastic crystals are discussed. A method for determining both the elastic constants and the spacial orientation of the crystal from the light scattering data is presented.
Measurements of sound velocity at 10 MHz in both liquid and solid tetradeuteromethane (CD(,4)) and cyclohexane (C(,6)H(,12)) are described. The elastic constants of CD(,4) at 85.57 K are found to be C(,11) = 2.056 (+OR-) .015, C(,12) = 1.542 (+OR-) .015, C(,44) = 0.9387 (+OR-) .005 GPa. For cyclohexane at 278.6 K the results of the measurements are C(,11) = 2.5795 (+OR-) .015, C(,12) + 2C(,44) = 2.967 (+OR-) .03 GPa. It is argued that the separate elastic constants of cyclohexane are C(,12) = 2.251, C(,44) = 0.358 GPa.
The presence of dispersion in the case of cyclohexane and its absence in the case of methane is noted. Some peculiarities in the elastic behavior of plastic crystals are discussed in the light of an expected coupling between translational and orientational excitations in the crystal.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.
|Date Available in IDEALS:||2015-05-13|