Thermodynamic properties of the high-pressure phases in solid nitrogen close to phase transitions

Akay, Özge
In this thesis,the physical properties of solid nitrogen are investigated in a wide range of temperature and pressure by analyzing experimental data from the literature.For this investigation, various models are implemented to the experimental data in order to evaluate observed behavior of thermodynamic and spectroscopic properties of solid nitrogen. By means of the calculating Grüneisen parameter which depends on the volume, the pressure and temperature dependence of the Raman and IR frequencies are estimated for the internal(vibrons) and external modes (lattice) of solid nitrogen. Especially, the mean field theory based on Landau phenomenological model is used to calculate P-T phase diagram of solid nitrogen. Also by using this model, we estimate the inverse susceptibility, the entropy, the heat capacity and the thermal expansion as a function of temperature close to the phase transition. Regarding to evaluation of the thermodynamic properties, we also predict temperature dependence of the thermodynamic functions from frequency shift and volume data which are obtained from literature and we use the Pippard relations to establish linearity for thermodynamic and spectroscopic quantities. As another calculation, we calculated the frequency shift and damping constant (FWHM) as a function of pressure via the anharmonic self energy. According to the evaluation of spectroscopic properties (frequency shift, damping constant) , we also use the pseudospin-phonon coupling (PS) and the energyfluctuation (EF) models to obtain the damping constant as a function of temperature at constant pressures. The inverse relaxation time and the activation energy as a function of temperature are also calculated close to the phase transition. In addition to these calculations, we analyze the thermodynamic and dielectric properties at various pressures and temperatures by using the Raman frequencies of cubic gauche solid nitrogen. All these calculations indicate that the methods used for analysis can also be applied to some other molecular solids close to phase transitions.


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Citation Formats
Ö. Akay, “Thermodynamic properties of the high-pressure phases in solid nitrogen close to phase transitions,” Ph.D. - Doctoral Program, Middle East Technical University, 2020.