A Caltech Library Service

Atomic Dynamics in Solids and Liquids from Inelastic Neutron Scattering


Bernal-Choban, Camille Marie (2024) Atomic Dynamics in Solids and Liquids from Inelastic Neutron Scattering. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3nv3-g144.


As temperature increases, atomic scale disorder, or entropy, drives the thermophysical properties of materials. One way it does this is by passing heat through materials in the form of vibrations. In solids, vibrational motions are called phonons, and their behaviors are used to predict macroscopic properties such as thermal expansion and thermal conductivity. Vibrational dynamics also exist in liquids but are traditionally less studied. Other forms of entropy include configurational and electronic entropy, which also evolve with temperature. Configurational changes in solids are often small, but in liquids, the prominence of diffusion makes this contribution significant. This dissertation addresses these atomistic components of entropy in two studies, one on bcc chromium and the other on the melting of monatomic systems.

In the first study, phonon densities of states (DOS) of body-centered cubic chromium were measured by time-of-flight inelastic neutron scattering (INS) at temperatures up to 1493 K. Density functional theory calculations with both quasi-harmonic (QH) and anharmonic (AH) methods were performed at temperatures above the Neel temperature. Features in the phonon DOS decrease in energy (soften) substantially with temperature. A Born-von Karman analysis using fits to the experimental DOS reveals a softening of almost 17% of the high transverse phonon branch between 330 and 1493 K. The low transverse branch changes by approximately half this amount. The AH calculations capture the observed behavior of the two transverse phonon branches, but the QH calculations give some inverted trends. Vibrational entropies from phonons and electrons are obtained, and their sum is in excellent agreement with the entropy of chromium obtained by calorimetry, indicating that above 330 K, no explicit temperature-dependent magnetic contributions are necessary.

The second investigation delves into the latent heat of melting, defined as TmΔSfus where Tm is the melting temperature and ΔSfus is the entropy of fusion. At the scale of atoms and electrons, ΔSfus has components from changes of atom configurations, atom vibrations, and thermal excitations of electrons. New data analyses were developed for inelastic neutron scattering to obtain changes in vibrational spectra upon melting. Combining these INS experiments with computational work using thermodynamic integration and molecular dynamics, components of ΔSfus were obtained for a total of six elements, Ge, Si, Bi, Sn, Pb, Li. Upon melting, there is always a positive change of configurational entropy, ΔSconfig. A baseline value of ΔSconfig=1.2kB/atom, approximately the value for Richard's rule, corresponds to zero change in the vibrational part of the entropy of fusion, ΔSvib. Elements having values of ΔSfus that depart from this value of Richard's rule have both an additional ΔSvib and an additional ΔSconfig. Surprisingly, the extra ΔSconfig is close to 77% of ΔSvib, for both positive and negative deviations from Richard's rule. This implies a correlation between the change in the number of basins in a potential energy landscape and the change in the inverse of their curvature upon melting.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:thermodynamics, inelastic neutron scattering, first principles calculations
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Fultz, Brent T.
Thesis Committee:
  • Faber, Katherine T. (chair)
  • Falson, Joseph
  • Granroth, Garrett
  • Fultz, Brent T.
Defense Date:18 September 2023
Non-Caltech Author Email:cmbchoban (AT)
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG02-03ER46055
Record Number:CaltechTHESIS:09222023-185858765
Persistent URL:
Related URLs:
URLURL TypeDescription Adapted for Ch. 3
Bernal-Choban, Camille Marie0000-0001-7550-3153
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16186
Deposited By: Camille Bernal-Choban
Deposited On:25 Sep 2023 17:55
Last Modified:12 Jun 2024 20:39

Thesis Files

[img] PDF - Final Version
See Usage Policy.


Repository Staff Only: item control page