The lambda-phase transition in NH4Br

Date

1996-01-01

Author

Yurtseven, Hasan Hamit
Sherman, WF

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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.

Subject Keywords

Instrumentation, General Materials Science

URI

https://hdl.handle.net/11511/56241

Journal

PHASE TRANSITIONS

DOI

https://doi.org/10.1080/01411599608207842

Collections

Department of Physics, Article

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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.
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.
The lambda-phase transitions in NH4Cl Yurtseven, Hasan Hamit (Informa UK Limited, 1995-01-01) 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-phas...
A mean-field model for the phase diagram of liquid crystals Tublek, A; Yurtseven, Hasan Hamit; Salihoglu, S (Informa UK Limited, 1998-01-01) In this study we have developed a mean-field model to obtain the phase diagram for a mixture of liquid crystals. Our mean-field model gives the phase diagram of the nematic, smectic A and smectic C phases near the NAC point. We have fitted our model to the experimentally observed data. From this fitting, we conclude that our mean-field model explains correctly the experimentally observed behavior of a mixed liquid crystalline system near the NAC point.
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.

Citation Formats

H. H. Yurtseven and W. Sherman, “The lambda-phase transition in NH4Br,” PHASE TRANSITIONS, pp. 137–146, 1996, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/56241.