Yazar "Yurtseven, Hasan Hamit" seçeneğine göre listele

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    Analysis of the specific heat of Ru Doped LiKSO4 close to phase transitions
    (Maik Nauka/Interperiodica/Springer, 2018) Yurtseven, Hasan Hamit; Tırpancı, D. V.; Karaçalı, Hüseyin
    The temperature dependence of the specific heat, C (p) , is analyzed for different percentages of ruthenium (Ru) content in LiKSO4 using a power-law formula deduced from Ising model. For this analysis, data observed are taken from the literature and the values of the critical exponent for C (p) are extracted in the vicinity of the transition temperature (T (c) = 708 K) within the incommensurate phase of Ru doped LiKSO4. Obtained values of the critical exponent of C (p) confirm in most cases above and below C (p) the critical exponent value predicted by the 3D Ising model for the doped LiKSO4. On this basis, the specific heat, C (p) , of some other molecular crystals can also be analyzed using the same power-law formula as studied here.
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    Calculation of the damping constant and activation energy for raman modes in (NH4)2SO4
    (World Scientific Publ Co Pte Ltd, 2011) Yurtseven, Hasan Hamit; Karaçalı, Hüseyin; Kiracı, Ali
    The temperature dependence of the damping constant is calculated for various Raman modes in (NH4)(2)SO4 by the expressions derived from the soft mode hard mode coupling model and the energy fluctuation model. The expressions for the damping constant are fitted to the measured Raman bandwidths and then the activation energies are extracted, which are equal to similar to 0.2 eV for the Raman modes studied. The damping constant of a soft mode is also calculated and the activation energy (similar to 0.1 eV) is deduced in this crystal. Values of the activation energies obtained here, can be compared with the value of k(B)T(C) = 0.02 eV for (NH4)(2)SO4. This indicates that this ferroelectric material undergoes an order disorder transition. It is concluded that the observed behaviour of (NH4)(2)SO4 can be described reasonably by the soft mode hard mode coupling model considered here.
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    Calculation of the free energies for the solid phases of ammonium halides
    (Taylor & Francis Ltd, 2007) Salihoğlu, S.; Yurtseven, Hasan Hamit; Karaçalı, Hüseyin
    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 is also predicted from the mean field theory.
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    Calculation of the Raman frequency and the damping constant of a coupled mode in the ferroelectric and paraelectric phases in KH(2)PO(4)
    (Wiley-V C H Verlag Gmbh, 2010) Karaçalı, Hüseyin; Kiracı, Ali; Yurtseven, Hasan Hamit
    The Raman frequency of the coupled mode omega_ associated with the order parameter is calculated as a function of pressure from the mean field theory in the ferroelecric phase of KDP. Using the frequencies of the coupled mode, the pressure dependence of the damping constant Gamma_ is calculated by the proton spin lattice relaxation time and by the energy fluctuation of this mode of KDP in the ferroelectric (FE) phase. For the paraelectric (PE) phase, the Raman frequency of the coupled mode omega is calculated as a function of temperature at 6.54 kbar. The temperature dependence of the damping constant Gamma_ is performed only by the energy fluctuation of the coupled mode omega_ in the PE phase of KDP. The values of the activation energy U are extracted from the pressure and temperature dependence of the damping constant Gamma_ of this coupled mode omega_ for both FE and PE phase of KDP. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    A linear variation of the thermal expansivity with frequency shifts for the translational mode in ammonia solid II near the melting point
    (Pergamon-Elsevier Science Ltd, 2007) Yurtseven, Hasan Hamit; Karaçalı, Hüseyin
    We examine here our spectroscopic modification of the Pippard relation which is a linear variation of the thermal expansivity alpha(p) with the frequency shifts (1/nu)(partial derivative nu/partial derivative p)(T) close to the melting point in ammonia solid II. For this we use our calculated frequencies for the Raman mode of nu (51 cm(-1)) in ammonia solid II for the pressures of 3.65, 5.02 and 6.57 kbars. We establish this linearity between alpha(p) and (I/nu)(partial derivative nu/partial derivative(p))(T) for the pressures studied in ammonia solid II close to the melting point. The observed behaviour of ammonia solid II is explained in terms of our spectroscopic relation given here. (C) 2007 Elsevier B.V. All rights reserved.
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    Linewidth of phonons in order-disorder phase transitions with random telegraph noise
    (World Scientific Publ Co Pte Ltd, 2011) Karaçalı, Hüseyin; Yurtseven, Hasan Hamit
    We derive an expression for the linewidth of phonons involved in the order phase transitions in solids. The linewidth is obtained as a function of the dwell time from which the activation energy can be computed. A new viewpoint is presented on the assumption that the fluctuations in the random variable of the noise, which is carried by the random particles involved in the order disorder mechanism, affect the linewidth of the phonons.
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    Raman linewidths calculated as a function of temperature in NaNO2
    (Wiley-V C H Verlag Gmbh, 2009) Karaçalı, Hüseyin; Yurtseven, Hasan Hamit; Kiracı, Ali
    The temperature dependence of the damping constant is calculated for some Raman modes in NaNO2 using the soft mode-hard mode coupling model and the energy fluctuation model. The damping constant is fitted to the measured Raman bandwidths of those modes, which is well described by the soft mode-hard mode coupling model. The values of the activation energy are extracted from the damping constant for the Raman modes, which are much greater than k(B)T(C) = 0.04 eV for NaNO2 close to the transition temperature (T-C = 436 K). This is an indication that NaNO2 undergoes an order-disorder phase transition. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Specific heat and frequency shifts for the translational modes in ammonia solid I close to phase transition
    (Pergamon-Elsevier Science Ltd, 2007) Yurtseven, Hasan Hamit; Karaçalı, Hüseyin
    The specific heat C-p is correlated to the frequency shifts (1/v)(partial derivative v/partial derivative T)(p) in ammonia solid I close to the melting point. Our calculated Raman frequencies for the translational modes of v(T) (100 cm(-1)) and v(T) (130 cm(-1)), are used for this correlation for the pressures of 0, 1.93 and 3.07 kbar in this crystalline system. We obtain that the specific heat varied linearly with the frequency shifts for those pressures studied and values of the slope dP(m)/dT were extracted. The observed behaviour of the ammonia solid I near the melting point is explained on the basis of our spectroscopic modification of the first Pippard relation. (C) 2006 Elsevier B.V. All rights reserved.
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    Temperature and pressure dependence of molar volume in solid phases of ammonia near the melting point
    (Elsevier Science Bv, 2008) Yurtseven, Hasan Hamit; Karaçalı, Hüseyin
    Temperature and pressure dependencies of the molar volume are studied here along the transition curve between solid I and solid II phases near the melting point in ammonia. The molar volumes are calculated in the temperature range of 217 to 224 K and in the pressure range of 3 to 8 kbar with respect to the triple point (T-t=217.34 K. P-t=3.070 kbar) where the melting curves of solid I and solid II coincide with the transition curve in ammonia. (C) 2008 Elsevier B.V. All rights reserved.
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    Temperature and pressure dependence of the mode Gruneisen parameters close to the melting point in hexagonal ice
    (Pergamon-Elsevier Science Ltd, 2007) Karaçalı, Hüseyin; Yurtseven, Hasan Hamit
    We reexamine the Pippard relations in this study by relating the specific heat C-P to the Raman frequency shifts 1/v(partial derivative v/partial derivative T)(P) and the thermal expansivity alpha(p) to the 1/v(partial derivative v/partial derivative P)(T), when the mode Gruneisen parameter depends on the temperature and pressure close to the melting point in hexagonal ice. From linear relations between them, the values of the slope dP/dT are deduced in this crystal. Our slope values calculated here do not change significantly compared to those obtained when the mode Gruneisen parameter is taken as a constant close to the melting point in hexagonal ice. (c) 2006 Elsevier B.V. All rights reserved.
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    Temperature dependence of the mode Grüneisen parameter in the vicinity of the ?-transition point in NH4Cl
    (Scientific Publ-India, 2006) Karaçalı, Hüseyin; Yurtseven, Hasan Hamit
    This study gives our relations between the specific heat C P and the Raman frequency shifts (1/v)(partial derivative v/partial derivative T)(p) for the lattice modes of v(5) (144 cm(-1)) and v(5) (174 cm(-1)), when the mode Gruneisen parameter gamma(p) depends on the temperature near. the lambda-transition in NH4Cl (T-lambda = 242.5 K, P = 0). From our linear relations between C-p and (1/v)(partial derivative v/partial derivative T)(p), we deduce the values of the slope (dP/dT)(lambda) for both lattice modes in this crystal. Our (dP/dT)(lambda) values remain almost the same as those which we calculate when gamma(p) is taken as a constant close to the lambda-transition in NH4Cl. Our calculated values for (dP/dT)(lambda) are reasonable in compared to the experimental values.