Calculation of phase diagrams and the thermodynamic quantities from the mean field models close to phase transitions in molecular and liquid crystals

Şen, Sema
This study gives our calculations for the temperature-pressure and temperature-concentration phase diagrams using the mean field models applied to ammonium halides (NH4Cl, ND4Cl), ammonium sulfate ((NH4)2SO4/H2O), lithium potassium rubidium sulfate (LiK1-xRbxSO4), potassium pyrosulfate-potassium hydrogensulfate (K2S2O7-KHSO4), cholestanyl myristate-cholesteryl myristate (CnM-CrM), cholestanyl myristate-cholesteryl oleate (CnM-CO), benzene (C6H6) and ice. The phase line equations are derived from the free energies expanded in terms of the order parameters and they are fitted to the experimental data. Some thermodynamic quantities are calculated close to phase transitions in these crystalline systems. We also calculate the specific heat CV using the Raman frequency shifts for NH4Br on the basis of an Ising model close to the lambda-phase transition. A linear relationship is obtained between the specific heat CP and the frequency shifts (1/v)(dv/dT)P near the lambda-point in NH4Br.


Development of atomic force microscopy system and kelvin probe microscopy system for use in semiconductor nanocrystal characterization
Bostancı, Umut; Turan, Raşit; Department of Physics (2007)
Atomic Force Microscopy (AFM) and Kelvin Probe Microscopy (KPM) are two surface characterization methods suitable for semiconductor nanocrystal applications. In this thesis work, an AFM system with KPM capability was developed and implemented. It was observed that, the effect of electrostatic interaction of the probe cantilever with the sample can be significantly reduced by using higher order resonant modes for Kelvin force detection. Germanium nanocrystals were grown on silicon substrate using different g...
Formation of semiconductor nanocrystals in sio2 by ion implantation
Serincan, Uğur; Turan, Raşit; Department of Physics (2004)
In this study, we used ion implantation technique to synthesize semiconductor (Ge, Si) nanocrystals in SiO2 matrix. Ge and Si nanocrystals have been successfully formed by Ge and Si implantation and post annealing. Implanted samples were examined by characterization techniques such as TEM, XPS, EDS, SAD, SIMS, PL, Raman and FTIR spectroscopy and the presence of Ge and Si nanocrystals in the SiO2 matrix has been evidenced by these measurements. It was shown that implantation dose, implantation energy, anneal...
Calculation of the specific heat for the first order phase transition in NH4Br
Yurtseven, Hasan Hamit; Sherman, WF (World Scientific Pub Co Pte Lt, 1998-11-01)
We calculate in this work the specific heat C-VI using the predictions of an Ising model for the NH4Br crystal (T-C = 234 K, P = 0). Our calculated C-VI values are in good agreement with the experimentally observed C-p data from the literature. This shows that the observed behavior of NH4Br can be described adequately in the lattice region under an Ising model studied here.
Calculation of the Raman frequencies of lattice modes in the disordered phase II of NH4Br at high pressures
Yurtseven, Hasan Hamit (Physics Essays Publication, 2010-01-01)
The Raman frequencies are calculated here at various temperatures for the nu(7) (56 cm(-1)) and nu(5) (134 cm(-1)) lattice modes in the disordered phase II of NH4Br. The lattice parameter data obtained at zero pressure are used to calculate the Raman frequencies of those modes studied for constant pressures of 0.1, 108, and 637.5 MPa in phase II of the NH4Br crystal. Through the mode Gruumlneisen parameter which is kept constant in the disordered phase II, the Raman frequencies calculated decrease linearly ...
Calculation of the free energies for the solid phases of ammonium halides
Salihoglu, S.; Yurtseven, Hasan Hamit; Karacali, H. (Informa UK Limited, 2007-01-01)
Using mean field theory, we calculate the free energies of the solid phases of ammonium halides. The temperature and pressure dependences of the free energies are obtained using experimental phase diagrams of the ammonium halides. From these dependences, we calculate numerically the specific heat as a function of temperature for the solid I-liquid, solid II-liquid and solid I-solid II transitions in the ammonium halides, in particular for NH4Cl. The critical behaviour of some other thermodynamic quantities ...
Citation Formats
S. Şen, “Calculation of phase diagrams and the thermodynamic quantities from the mean field models close to phase transitions in molecular and liquid crystals,” Ph.D. - Doctoral Program, Middle East Technical University, 2009.