Heat capacity, entropy, formation energy and spin-fluctuation behavior of U₃Si₅ from 2.4 to 397.4 K

U-Si intermetallic compounds are of considerable interest for their applications as accident-tolerant nuclear fuels. Here we present low-temperature heat capacity (LTHC) measurements of one of the U-Si phases, U₃Si₅, using a Quantum Design Physical Properties Measurement System (PPMS) from 2.4 to 397.4 K. We observed an upturn in C_p/T (T) below 10 K and have attributed this behavior to potential spin-fluctuations (SF) with an SF temperature (T_sf) of 27 K. An enhancement of LTHC was also observed, as manifested by a large electronic heat capacity coefficient (γ_el) of 342.9 mJ/mol•K². From the heat capacity data, the following thermodynamic parameters were determined: the characteristic Debye temperature (θ_D) over the temperature range 30 – 397 K is 177 ± 2 K, and the standard entropy (Δ₀^298.15S^∘) is 283.3 ± 5.7 J•mol⁻¹•K⁻¹ (equivalent to 35.4 ± 0.7 J•mol⁻¹•atom⁻¹•K⁻¹). Combined with our previously measured formation enthalpy (Δ_fH_el^∘) of U₃Si₅, the Gibbs free energy of formation of U₃Si₅ from the elements (Δ_fG_el^∘) was determined to be –45.2 ± 9.0 kJ•mol⁻¹•atom⁻¹.