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.