A quantum mechanical study of the phase stability and phase transition mechanisms in CaCO3 at finite temperature and pressure
File(s)
Author(s)
Carrasco de Busturia, David
Type
Thesis
Abstract
First-principles calculations have been performed to explore
the temperature-pressure phase diagram of calcium carbonate (CaCO3) in a range of temperatures and pressures up to 1000 K and 10 GPa respectively. The calcite I - calcite II and calcite I - aragonite phase boundaries have been obtained. Imaginary phonon modes in the aragonite phase suggest pathways to three distinct alternative phases that involve symmetry breaking and distortion of the unit cell. The variation of the Gibbs free energy with pressure and temperature has been computed in the quasi-harmonic approximation. Several approaches have been discussed in this thesis for the most accurate determination of the temperature - pressure phase boundary. A method for determining the calcite I - calcite II second order phase boundary has been described in this work. Hybrid exchange and GGA density functional theory in the all-electron linear combination of atomic orbitals approximation have been exploited, as well as the effect of the inclusion of van der Waals dispersion corrections. The resultant theoretical phase diagram is compared to the available measurements. The detailed theoretical understanding of the phase transitions mechanisms developed in this thesis sets the basis for a future exploration of the thermodynamic stability phase of CaCO3. In this respect, the methodology described in this work could be used to predict the temperature - pressure phase boundaries of the rest of the polymorphs of this complex system, e.g. phase transitions occurring in calcite III, IIIb, IV, V and VI.
the temperature-pressure phase diagram of calcium carbonate (CaCO3) in a range of temperatures and pressures up to 1000 K and 10 GPa respectively. The calcite I - calcite II and calcite I - aragonite phase boundaries have been obtained. Imaginary phonon modes in the aragonite phase suggest pathways to three distinct alternative phases that involve symmetry breaking and distortion of the unit cell. The variation of the Gibbs free energy with pressure and temperature has been computed in the quasi-harmonic approximation. Several approaches have been discussed in this thesis for the most accurate determination of the temperature - pressure phase boundary. A method for determining the calcite I - calcite II second order phase boundary has been described in this work. Hybrid exchange and GGA density functional theory in the all-electron linear combination of atomic orbitals approximation have been exploited, as well as the effect of the inclusion of van der Waals dispersion corrections. The resultant theoretical phase diagram is compared to the available measurements. The detailed theoretical understanding of the phase transitions mechanisms developed in this thesis sets the basis for a future exploration of the thermodynamic stability phase of CaCO3. In this respect, the methodology described in this work could be used to predict the temperature - pressure phase boundaries of the rest of the polymorphs of this complex system, e.g. phase transitions occurring in calcite III, IIIb, IV, V and VI.
Version
Open Access
Date Issued
2018-11
Date Awarded
2019-03
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Harrison, Nicholas
Sponsor
European Union
Grant Number
Marie Sklodowska-Curie grant agreement No 642976
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)