The lambda-phase transitions in NH4Cl

Date

1995-01-01

Author

Yurtseven, Hasan Hamit

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We show here the correlations between the volume changes and the vibrational frequencies of the disorder-induced Raman modes of NH4Cl near the lambda-phase transitions of first order (P=0), tricritical (P similar or equal to 1.6 kbar) and second order (P similar or equal to 2.8 kbar). We obtain the values of the mode Gruneisen parameter for each phonon across the lambda-phase transitions and use them to predict the Raman frequencies for the phonon modes studied as functions of temperature in the lambda-phase change regions.

Subject Keywords

Instrumentation, General Materials Science

URI

https://hdl.handle.net/11511/57271

Journal

PHASE TRANSITIONS

DOI

https://doi.org/10.1080/01411599508200400

Collections

Department of Physics, Article

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The lambda-phase transition in NH4Br Yurtseven, Hasan Hamit; Sherman, WF (Informa UK Limited, 1996-01-01) This study gives the predicted frequencies for the Raman modes of v(7)TA(56 cm(-1)), v(5)LO(177 cm(-1)) and v(2)(1684 cm(-1)) of NH4Br at various temperatures for zero pressure across the lambda-phase transition in this crystal system. We calculate the Raman frequencies by means of a constant mode Gruneisen parameter for each mode across the lambda-phase change region of NH4Br.
Ultrasonic frequencies correlated with the volume changes of the q[1(1)over-bar-0] mode for the first-order phase transition in NH4Cl Yurtseven, Hasan Hamit (Informa UK Limited, 2000-01-01) We correlate here by means of gamma-Gruneisen relations the volume changes with the ultrasonic frequencies of the q[1 (1) over bar 0] mode of NH4Cl for the first-order phase transition in this crystal. The ultrasonic frequencies were calculated by a method, which we have developed, using the length-change data from the literature at pressures of 0, 0.2, 0.3 and 0.6 kbar in the first-order phase region of NH4Cl.
The mean field model with P-2 theta(2) coupling for the smectic A-smectic C* phase transition in liquid crystals Salihoglu, S; Yurtseven, Hasan Hamit; Giz, A; Kayisoglu, D; Konu, A (Informa UK Limited, 1998-01-01) Using mean field theory with a P(2)theta (2) coupling term in the free energy expansion, we calculate the polarization as a function of temperature for the smectic A-smectic C* phase transition in a liquid crystalline material. Our calculated polarization values are in good agreement with the experimental data.
T-X-Br phase diagram for the NH4BrxCl1-x system Tari, O; Yurtseven, Hasan Hamit; Salihoglu, S (Informa UK Limited, 2000-01-01) In this study using a mean field model we calculate the phase line equations for the beta-delta, beta-gamma and gamma-delta phase transitions in the NH4BrxCl1-x system. We then fit our phase line equations to the experimentally observed T-X-Br phase diagram for this system. Our calculated phase diagram agrees well with the observed one for the NH4BrxCl1-x system.
A phase diagram near the NAC* point in liquid crystals Salihoglu, S; Tublek, A; Yurtseven, Hasan Hamit (Informa UK Limited, 2000-01-01) Wt study here a mean field model to obtain the phase diagram (concentration versus temperature) near the NAC* point in a binary mixture of liquid crystal. Wr have Fitted our phase line equations to the experimental data for the mixture of SCE9 + SCE10 liquid crystals. We deduce fi om our analysis that there should exist a tricritical point close to the NAC* point on the AC* phase line.

Citation Formats

H. H. Yurtseven, “The lambda-phase transitions in NH4Cl,” PHASE TRANSITIONS, pp. 1–13, 1995, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/57271.