GENERAL THERMODYNAMIC TREATMENT OF AMMONIUM-CHLORIDE SYSTEM CLOSE TO PHASE-TRANSITIONS

Date

1986-03-01

Author

Yurtseven, Hasan Hamit

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In ammonium halides the optical and acoustical phonons may be represented by the Einstein and Debye models. Close to the λ-phase-transition, the model for the lattice vibrations in these crystals requires an extra component which can be described by an Ising model. In this study we have developed an Ising model superimposed on an Einstein and/or Debye model and have applied it to the NH4Cl system. In this application we have used the Raman frequency of the ν5(174cm−1) phonon of NH4Cl to characterize the corresponding Einstein and Debye frequency for this crystal system. Thus from our observed frequencies for the 174cm−1 (TO) mode we have obtained an approximation for the lattice vibrational contribution to the specific heat Cy of NH4Cl. The critical behaviour of the specific heat has been obtained for the Ising model, since the Einstein or Debye model is considered to show no anomaly in Cv near the phase transition. The predicted values are close to observed Cp data but differ significantly from the only observed Cv data available, (Sakamoto, 1954) It is suggested that the observed Cy data is unreliable in the vicinity of the λ-transition. The present model, or modifications of it should be capable of giving quite precise descriptions of the thermodynamic properties of solids close to second-order (or nearly second-order) phase transitions.

Subject Keywords

Chemistry, Physical

URI

https://hdl.handle.net/11511/56521

Journal

JOURNAL OF MOLECULAR STRUCTURE

DOI

https://doi.org/10.1016/0022-2860(86)85195-x

Collections

Department of Physics, Article

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Citation Formats

H. H. Yurtseven, “GENERAL THERMODYNAMIC TREATMENT OF AMMONIUM-CHLORIDE SYSTEM CLOSE TO PHASE-TRANSITIONS,” JOURNAL OF MOLECULAR STRUCTURE, pp. 21–24, 1986, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/56521.