Experimental determination of the enthalpy of formation of the pyrochlore rare-earth hafnates

In this study, enthalpies of formation of compounds RE2Hf2O7 type (where RE = La, Pr, Nd, Sm, Eu, and Gd), with pyrochlore structure have been measured by high-temperature oxide melt solution calorimetry. Results were compared with literature data, and dependencies of enthalpies of the formation of compounds with the pyrochlore structure from the ionic radius of rare-earth element were analyzed. The enthalpy of formation becomes more positive with the increase in ionic radius, which is in conformity with the results earlier observed for titanates and zirconates.