Thermodynamics of the lanthanide trifluorides. I. The heat capacity of lanthanum trifluoride, LaF3 from 5 to 350°K and enthalpies from 298 to 1477°K

Abstract

The heat capacity of a sample of LaF₃ was determined in the temperature range 5–350°K by aneroid adiabatic calorimetry and the enthalpy from 298.15 to 1477°K by drop calorimetry. The heat capacity at constant pressure C°_p(298.15°K), the entropy S° (298.15°K), the enthalpy [H° (298.15°K)−H° (0)] and the Planck function −[G° (298.15°K)−H° (0)]/298.15°K; were found to be (90.29±0.09) J °K⁻¹⋅mole⁻¹, (106.98±0.11) J °K⁻¹⋅mole⁻¹, (16717±17) J mole⁻¹, and (50.91±0.05) J °K⁻¹⋅mole⁻¹. The thermal functions from the present research were extended up to the melting temperature (1766°K) by combination with previously published results. The anomalously high heat capacity from about 1100 to 1766°K is discussed.