RAMAN FREQUENCY SHIFTS CLOSE TO THE $\nu$-PHASE TRANSITION IN THE NH$_4$Br
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Date
2005
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Ohio State University
Abstract
The critical behavior of the frequency shifts for the Raman modes of $\nu_7$ (56 cm$^{-1}$) and $\nu_2$ (1684 cm$^{-1}$) in NH$_4$Br is analyzed here close to the $\lambda$-phase transitions (T$_\lambda =234$K, P=0) in this crystalline system. Values of the critical exponent associated with the critical behavior of the frequency shifts $\frac{1}{\nu} \left(\frac{\partial\nu}{\partial T} \right)_P$ are deduced for T$<$T$_\lambda$ and T$>$T$_\lambda$ in NH$_4$Br. Our exponent values can be compared with those obtained experimentally for the specific heat C$_p$ and the thermal expansivity $\alpha_P$ close to the $\lambda$-phase transition in NH$_4$Br.
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Author Institution: Department of Physics, Middle East Technical University 06531; Ankara-Turkey