RAMAN FREQUENCIES OF THE TA PHONON MODE OF $NH_{4}Cl$ CLOSE TO PHASE TRANSITIONS

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1992

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Ohio State University

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The Raman spectra of $TA_{M}$ ($93 cm^{-1}$) lattice mode of $NH_{4}Cl$ were obtained as functions of temperature in

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the tricritical (P$\mathop{}^{\rightarrow}\kern -10 pt{_\leftarrow} 1.6 kbar^{4}$) and in the second order (P$\mathop{}^{\rightarrow}\kern -10 pt{_\leftarrow}$2.8 kbar) phase region. Our Raman data indicate a small discontinuity accompanied with continuity in the frequency shifts at $\simeq$ 1.6 kbar (tricritical). At $\simeq$ 2.8 kbar this discontinuity seems to disappear as the system changes its phase from a first order to a second order one. The Raman spectra of the $TA_{M}$ ($93 cm^{-1}$) mode of $NH_{4}Cl$ are presented.
Author Institution: Department of Physics, Istanbul Technical University; Department of Physics, King's College London

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