The specific heat of terbium and erbium trihydrides

Specific heat measurements were made in the temperature range of 2–300 K on TbH3 and ErH2.98 trihydride samples. The magnetic Schottky anomaly was separated from the experimental Cp(T)Cp(T) data by subtracting the lattice heat contribution of the non-magnetic LuH3 hydride. The Schottky contribution was explained by the effect of the crystal field on the magnetic ions. The full splitting of the crystal field level was determined for the Tb3+ ion in TbH3 as δE=573K with the singlet Γ1Γ1 ground state. The overall energy splitting of the Er3+ ion in ErH3 is much larger and cannot be determined directly from Schottky contribution analysis. Nevertheless, the doublet seems to be the ground state and the magnetic contribution in the specific heat is determined by thermal excitations within five of the eight possible crystal field energy levels in ErH2.98 trihydride.The polynomial functions to fit the measured Cp(T)Cp(T) values are given. The thermodynamic functions of entropy and enthalpy for several temperatures are calculated.