The heat capacity of USn3

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Abstract
The heat capacity of USn3 was measured between 0.6 and 420 K. An unusually large linear term in the low‐temperature heat capacity was observed. The coefficient of this linear term was found to be 171 mJ/°K2‐mole, in excellent agreement with a recently reported calorimetric measurement above 1.5 K. An anomalous leveling off of C/T versus T 2 below 3.5 K reported in an earlier study was not found and, hence, is not an intrinsic property of USn3. Below 1.5 K, small anomalies were found in the heat capcaity of two samples with different impurity levels. At present, no auxiliary physical‐property measurements below 4 K are available to clarify the origin of the low‐temperature anomalies. Since C p ?3R[1‐1/20(ϑ∝/T)2]+γT at high temperatures, a value of the Debye temperature ϑ∝ of 196 K was determined from the slope of a (C p ‐3R)/T versus T −3 plot. The T −3=0 intercept of this plot indicates that at high temperatures the electronic heat‐capacity coefficient drops to ∠20 mJ/°K2‐mole, a value more typically associated with a conduction electron heat‐capacity contribution. The electronic entropy in excess of 20T mJ/°K‐mole that is removed at low temperatures is 1.05 R1n2. The accuracy to which the excess electronic entropy is known is quite sensitive to the model used to describe the lattice heat capacity. The one‐parameter harmonic representation used can introduce errors of the order of ±25% in the 1.05 R1n2 value. A rapid drop of γ from 171 to ∠20 by 80 K indicates the presence of unusual structure in the electronic density of states at the Fermi energy. It is proposed that USn3 is an interconfigurational‐fluctuation system.

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