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TY - THES AU - Stoffel, Ralf Peter TI - Voraussetzungsfreie Thermochemie kristalliner Festkörper CY - Aachen PB - Publikationsserver der RWTH Aachen University M1 - RWTH-CONV-143211 SP - VI, 79 S. : Ill., graph. Darst. PY - 2012 N1 - Aachen, Techn. Hochsch., Diss., 2012 AB - This work deals with an approach to calculate thermodynamic data without the need of experimental measurements. The data obtained can complete, verify or falsify experimental data used in thermochemical calculations. The Gibbs free energy is constructed from the Helmholtz free energy, because the theoretical calculations are carried out at constant volume. Temperature dependent contributions to the Helmholtz free energy were mainly based on the simulation of lattice dynamics. Some other smaller contributions were also included. In the first part the calculated data are compared with well-known experimental data to verify the method used. Temperature dependent heat capacities and entropies of some binary oxides showed good agreement with the data base values. Theoretically calculated vibrational spectra showed a good reproduction of Raman spectroscopic measurements in the case of Barium peroxide. Also mechanical properties, namely the bulk modulus of Barium oxide, showed good agreement with experimental values. The phase transition temperature of tin (alpha to beta) showed a small overestimation. Part two of the work deals with several more complex systems. These play a role by modeling the conditions of fabrication of the high temperature superconductor YBa2Cu3O6+x. The compounds were BaY2O4, Ba3Y4O9, BaCeO3, and the superconductor YBa2Cu3O6+x itself. The first three compounds were necessary to prove the reliability of the data base, which could be verified in most cases. In some cases there have to be made at least some critical considerations. Investigations of YBa2Cu3O6+x included the structure, which depends on Oxygen content x and temperature, the heat of formation and the Gibbs free energy of formation. The temperature and pressure dependent phase transition between the orthorhombic and tetragonal modification of YBa2Cu3O6.5 was obtained in good agreement with the literature. The Gibbs free energy of formation of YBa2Cu3O6+x from binary oxides and oxygen showed good agreement with a greater stabilization of the superconducting phase compared to an equation fitted to several thousand experimental values. KW - Ab-initio-Rechnung (SWD) KW - Thermochemie (SWD) KW - Gitterdynamik (SWD) KW - Festkörperchemie (SWD) KW - Dichtefunktionalformalismus (SWD) LB - PUB:(DE-HGF)11 UR - https://publications.rwth-aachen.de/record/82855 ER -