Li, Chen W. (2012) Phonon anharmonicity of ionic compounds and metals. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:05012012-155623422
Vibrational studies of materials at elevated temperatures are relatively rare, and most phonon work also has emphasized harmonic behavior. Non-harmonic effects are often unexplored. These non-harmonic effects can be important for many properties of the material, such as thermal transport and phase stability.
Phonon theory and computational methods are briefly reviewed, and the experimental techniques for phonon study, such as Raman spectroscopy and inelastic neutron scattering, are discussed. Several experiments on phonon anharmonicity were performed, and interpreted with these computational methods.
In Raman spectroscopy studies on the phonon dynamics of hafnia and zirconia, Raman line positions, and shapes of temperatures to 1000 K were measured and the types of modes that exhibit the most anharmonicity were characterized and correlated to the vibrational displacements of individual atoms in the unit cell. It was found that anharmonicity in these systems is rich in information and strongly mode dependent.
Using time-of-flight inelastic neutron scattering, we found purely quartic transverse modes with an anomalous mode stiffening with temperature, and related these modes to the enormous negative thermal expansion of the DO9 structure of scandium fluoride.
Using second-order perturbation theory, phonon linewidths from the third-order anharmonicity were calculated from first-principles density functional theory with the supercell finite-displacement method. For face-centered cubic aluminum, the good agreement between calculations and the phonon density of states up to 750 K indicates that the third-order phonon-phonon interactions calculated can account for the lifetime broadenings of phonons in aluminum to at least 80% of its melting temperature.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Subject Keywords:||phonon, anharmonicity, phonon lifetime, phonon linewith, negative thermal expansion, Raman, neutron scattering, lattice dynamics|
|Degree Grantor:||California Institute of Technology|
|Division:||Engineering and Applied Science|
|Major Option:||Materials Science|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||4 May 2012|
|Author Email:||chenwli (AT) gmail.com|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Chen Li|
|Deposited On:||22 May 2012 19:40|
|Last Modified:||26 Dec 2012 04:42|
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