Energetics of formation of KF-GdF3 binary-intermediate compounds

Enthalpies of formation were measured for KGdF4, K2GdF5 and KGd2F7 using the transposed temperature drop calorimetry method. These compounds were synthesized by conventional solid state reaction methods using mixtures of KF and GdF3. The measured enthalpies of formation from fluorides for KGdF4, K2GdF5 and KGd2F7 were -22.3, -16.1 and -18.3 kJ mol(-1), respectively. From these measurements, enthalpies of formation from the elements were computed to be -2290.0, -2852.4 and -3985.2 kJ mol(-1) for the respective compounds. These enthalpies were compared with estimated values calculated by two methods previously reported to be effective for multicomponent oxides. Estimated values compare favorably with measured data, with deviations ranging from 0.5 to 2.9%. The errors of 0.5-2.9% correspond to a 16-85 kJ mol(-1) uncertainty range for Delta(f)H(0) of ternary fluorides from binary fluorides. One of these methods, based on the summation of Delta(f)H(0) values for the constituent binary fluorides, is recommended for the K-Gd-F compounds.