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We discuss experimetal results of calorimetry on heavy-fermion compounds (HFC) with special regard to the f-derived specific heat ΔC . Attention is given to the extraction of Δ C and the uncertainties implied therein. The discussion includes some Ce-based 4f systems but concentrates on U-based 5f HFC. In four of these (UBe 13 , UPt 3 , URu 2 Si 2 , U 2 Zn 17 ) distinct anomalies in Δ C have recently been found in the temperature range between 20 and 100 K which we think are likely to be caused by crystal-field effects thus indicating strong 5f localization.

We present the results of calorimetric measurements of the specific heat in UBe13 and ThBe13 in the temperature range 20 K T 120 K. Combined with earlier results of inelastic neutron scattering, the data allow the extraction of the electronic specific heat ΔC in UBe13. ΔC shows a pronounced peak around 70 K which we interpret as a Schottky anomaly due to crystal-field splitting of a 5f3 ground-state configuration. Our results suggest the existence of highly localized 5f electrons in the heavy-fermion compound UBe13.

Measurements of the high-field dc magnetization and low-field ac susceptibility as well as specific-heat experiments covering almost four decades in temperature characterize CeAl 3 as a “dense Kondo system” with T k ≈ 5 K. From these results, the low-temperature value of the “Wilson ratio”, R (0) = 2.9, is deduced.

The specific heat of polycrystalline CeCu 2 Si 2 has been measured between 20 and 400 K and shows a contribution, which is tentatively ascribed to Schottky-defects with an activation energy of k B 1600 K. These defects might be the cause for the irregularities observed in CeCu 2 Si 2 at low temperature.

High-temperature specific heat measurements and an extensive study of the thermal-expansion coefficient on Ce 1− x Y x Al 2 reveal for x ⩽ 0.6 trivalent Ce-ions, which are subject to Kondo and crystal-field effects. A continuous transition into an intermediate valent state occurs for higher Y concentrations.

The f-electron contributions to the specific heats of CeCu2Ge2, CeRu2Ge2 and UBe13 were determined and show Schottky anomalies at temperatures between 50 and 250 K. From these the crystal-field splittings are deduced. The specific heat connected with the magnetic phase transition in CeRu2.16Ge2 was measured and a second anomaly observed, which points to a complicated magnetic order.

Specific-heat and thermal-expansion measurements on CeCu2Si2 samples of varying stoichiometry as well as on dilute (Ce, T)Cu2Si2 alloys (T:Y,La) indicate that the observed suppression of superconductivity in samples with “high” unit-cell volume is associated with a reduction of the Kondo temperature and the occurrence of another cooperative phenomenon, probably magnetic in origin.