Pippard relations modified by the Raman frequency shifts for the phases I and II in NH4I

✍ Scribed by H. Yurtseven

• Publisher: Elsevier Science
• Year: 2009
• Tongue: English
• Weight: 281 KB
• Volume: 924-926
• Category: Article
• ISSN: 0022-2860
• DOI: 10.1016/j.molstruc.2008.10.070

✦ Synopsis

Pippard relations in terms of the frequency shifts of the m 7 (40 cm À1 ) lattice mode, are established here for the phases I and II in NH 4 I. The temperature-induced frequency shift, (1/m)(om/oT) P is calculated through the isobaric mode Grüneisen parameter c P using the lattice parameter data at zero pressure for the phases I and II in NH 4 I. From the frequency shifts, the specific heat C P is calculated for the phases studied at zero pressure. Also, the pressure-induced frequency shift, (1/m)(om/oP) T is calculated through the isothermal mode Grüneisen parameter c T at 300 K and it is related to the thermal expansivity a P for the phases I and II in NH 4 I.

Linear variation of C P with the (1/m)(om/oT) P and also a linear variation of a P with the (1/m)(om/oP) T , indicate that the frequency shifts obtained for the m 7 (40 cm À1 ) lattice mode exhibit similar critical behaviour as C P and a P close to the I-II phase transition in NH 4 I.