Meslek Yüksek Okulları / Vocational Schools

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Start date: 1996Subject: search.filters.subject.quartz

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    Temperature dependence of the piezoelectric resonance frequency in relation to the anomalous strain near the incommensurate phase of quartz
    (2021) Ates, S; Yurtseven, H.
    The temperature dependence of the piezoelectric resonance frequency is analyzed by the power-law formula in the vicinity of the critical temperature of the incommensurate (INC) phase in quartz using the experimental data from the literature. By considering the piezoelectric resonance frequency as an order parameter of the INC phase, correlation between the piezoelectric resonance frequency and the strain is constructed, which both decrease linearly with increasing temperature toward T-c in quartz. Our results can explain dynamics of the ordering mechanism in the INC phase (within a very narrow temperature interval between the alpha and beta phases of quartz) and suggest a second order transition from INC to the beta phase in quartz.
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    Calculation of the damping constant and the relaxation time of the LA mode in the incommensurate phase of quartz
    (2021) Ates, S.; Yurtseven, H.
    The damping constant (linewidth) of the LA mode is calculated as a function of temperature for the incommensurate (INC) phase of quartz by using the models of the pseudospin-phonon (PS) coupled and the energy fluctuation (EF). For this calculation, the observed linewidth (Gamma(LA)) data are used at P = 0 and 80.5MPa from the literature. Close to the incommensurate phase between the alpha and beta phases of quartz, the observed Gamma(LA) and the frequency shifts (Delta v(LA) ) are also analyzed by the power-law formula for both pressures (P = 0 and 80.5MPa). By using the Gamma(LA) and Delta v(LA), the inverse relaxation time (tau(-1)(LA)) is predicted as a function of temperature (P = 0 and 80.5MPa) in the incommensurate phase of quartz and the values of the activation energy (E-a) are deduced. Our calculated Gamma(LA) from both models (PS and EF) explain adequately the observed behavior of the linewidth of the LA mode in the incommensurate phase of quartz. Also, our predicted tau(-1)(LA) can be compared with the measurements in the INC phase of this molecular crystal.
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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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    Landau mean-field model with the cubic term for the alpha-beta transition in quartz
    (2020) Ates, S.; Yurtseven, H.
    Thermodynamic quantities are calculated as a function of temperature by using Landau mean-field model for the alpha-beta transition in quartz. By expanding the Gibbs free energy in terms of the order parameter (Q) with the cubic term (Q(3)), the temperature dependence of the relevant thermodynamic quantities are predicted using the heat capacity (C-P), which is fitted to the experimental data from the literature for the alpha-beta transition in quartz. Our results indicate that the Landau mean-field model is adequate to describe the first-order alpha-beta transition in quartz.