The phase diagram of ammonium iodide (NH4I) under pressure, and a comparison with NH4Cl and NH4Br

• During recent measurements of thermal conductivity using the transient hot-wire method, data were obtained for pressure-temperature coordinates corresponding to transitions amongst phases I, II, III and IV of NH4I which extended reliable knowledge of the phase diagram to pressures of 2 GPa. Comparison of the phase diagrams of NH4Cl, NH4Br and NH4I showed that a generalised phase diagram covering these substances was a poor approximation if the higher-order critical points or triple points (as appropriate) were made coincident. However, the ferro-ordered-to-disordered phase transition boundaries of these substances could be made to follow a common curve with an alternative empirical adjustment of pressure and temperature. When this was done, the adjustments of temperature required were correlated with differences in barrier height opposing re-orientational motion of the ammonium species. 

Ämnesord

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Nyckelord

Phase diagram

thermal conductivity

high pressure

ammonium halides

NH4I

NH4Cl

NH4Br

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