Thermal conductivity and heat capacity of ammonium halides under pressure: NH4Br, NH4I and a comparison with NH4Cl

• The thermal conductivity lambda and heat capacity per unit volume rho cp have been measured for solid phases of NH4Br and NH4I using the transient hot-wire method in the temperature T range 100-400 K and at pressures P up to 2 GPa. Comparison of present results with those of previous work for NH4Cl showed similar heat conduction behaviour amongst these ammonium halides. Continuous or near-continuous phase transitions were indicated by an abrupt change in the derivative of lambda with respect to either T or P as well as by a maximum in rho cp. Lambda and rho cp changed discontinuously at the first-order I-II phase transition in NH4I. A decrease in NH4 orientational order was concluded to be mainly responsible for the observed increase of thermal resistivity W(= lambda -1) in both ferro- and antiferro-ordered phases during the isobaric temperature increase leading up to an order-disorder transition temperature. Negative (or near-negative) values of (delta lambda / delta P)T observed for the antiferro-ordered phases were consistent with corresponding negative values of thermal expansivity reported by other workers. 

Ämnesord

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

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

Nyckelord

Thermal conductivity

heat capacity

specific heat

high pressure

ammonium halide

NH4Br

NH4I

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