The specific heat of terbium and erbium trihydrides

Abstract Specific heat measurements were made in the temperature range of 2–300 K on TbH 3 and ErH 2.98 trihydride samples. The magnetic Schottky anomaly was separated from the experimental C p ( T ) data by subtracting the lattice heat contribution of the non-magnetic LuH 3 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 Tb 3+ ion in TbH 3 as δ E = 573 K with the singlet Γ 1 ground state. The overall energy splitting of the Er 3+ ion in ErH 3 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 ErH 2.98 trihydride. The polynomial functions to fit the measured C p ( T ) values are given. The thermodynamic functions of entropy and enthalpy for several temperatures are calculated.