Browsing by Author "Yurtseven, Hamit"

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    Landau phenomenological model for the alpha-INC (incommensurate)-beta transition in quartz
    (2021) Yurtseven, Hamit; Ates, Simge
    The temperature dependence of the order parameters eta (alpha-phase) and xi (INC - incommensurate phase) are calculated in the presence of the electric field for the alpha-INC-beta transition in quartz by the Landau mean field theory. Landau phenomenological model with the linear (eta xi) and quadratic (eta(2)xi(2)) coupling is introduced to investigate mainly the nature of the INC phase between alpha (ordered) and beta (disordered) phases in quartz. The temperature dependence of the inverse susceptibilities (chi(-1h)(eta) and chi(-1)(xi)) of the order parameter is also predicted at constant electric fields studied for the alpha-INC-beta transition in quartz. Additionally, the E-T phase diagram for the transitions of the alpha-INC and INC-beta in quartz is constructed from the Landau phenomenological model by using the literature data. Our predictions for the order parameters (eta and xi) and the inverse susceptibilities (chi(-1)(eta) and chi(-1)(xi)) can be compared with the experimental measurements for the alpha-INC-beta transition in quartz.
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    Thermodynamic And Dielectric Properties Of Hexagonal Barium Titanate Near The Phase Transitions
    (PHYSICA SCRIPTA, 2024-11-01) Yurtseven, Hamit; Kiraci, Ali
    The critical behavior of the thermodynamic quantities is studied for the two phase transitions near the transition temperatures (74 K and 222 K) in the hexagonal (h) BaTiO3. A linear relationship has been established between the variations of the frequency shifts and of the dielectric constant by using the literature data in h-BaTiO3. Temperature and pressure dependence of the mode Gr & uuml;neisen parameters ( gamma p and gamma T ) are also described by a power-law formula as the other thermodynamic parameters near Tpt in h-BaTiO3. Our results show that they explain the observed behavior adequately, in particular soft-mode frequency, dielectric constant, thermal expansion, the excess specific heat and the entropy near Tpt in h-BaTiO3. Temperature dependence of the isobaric mode Gr & uuml;neisen parameter ( gamma p ), enthalpy and the Gibbs free energy, which we have evaluated, can be compared with experiments in h-BaTiO3