Molar Heat Capacity of Potassium Alum KAl(SO4)(2) center dot 12H(2)O at Low Temperatures: Revisited with Determination of the Debye Temperature

Abstract

Two earlier published experimental data [C. H. Shomate, J. Am. Chem. Soc. 67, 765 (1945); D. G. Kapadnis and R. Hartmans, Physica 22, 173 (1956)] of the molar heat capacity C (p) of potassium alum, KAl(SO4)(2)center dot 12H(2)O, are revisited. From analysis of the temperature dependence of C (p) [D. G. Kapadnis and R. Hartmans, Physica 22, 173 (1956)] below 20 K by using the experimental values of C (p) represented as a plot of C (p) /T = gamma+AT (2), the Sommerfeld parameter gamma (electronic heat capacity coefficient) and the slope A (lattice heat capacity coefficient) are estimated as gamma = 0 JK (-2)mol (-1) and A = 3.35x10 (-3) JK (-4)mol (-1), respectively. This indicates that only acoustic phonons contribute to the heat capacity below 4 K. The Debye T (3)-law is found to hold good to 4 K, i.e., to T < theta (D) /20, where theta (D) is the calorimetric Debye temperature calculated as theta (D) = 83.4 K, indicative of the strength of the chemical bonding in the system.