Enthalpies of Formation and Thermal Expansion of Crystal Lattice of Compositionally Complex Rare‐Earth Zirconates

ABSTRACT Thermal expansion of the crystal lattice and thermodynamic properties (standard enthalpy and Gibbs energy of formation) for the compositionally complex zirconates have been investigated in the current work. Pyrochlore zirconates with the following compositions ((La,Gd)Zr 2 O 7, (La,Sm,Gd) 2/3 Zr 2 O 7 , (La,Sm,Y,Gd) 1/2 Zr 2 O 7 , (La,Nd,Sm,Y,Gd) 1/2 Zr 2 O 7 ) have been synthesized. Chemical and phase composition of the samples has been identified using SEM/EPMA and XRD. The standard enthalpies of formation have been measured using drop‐solution calorimetry. The thermal expansion of the crystal lattice has been obtained from the high‐temperature XRD data. The effect of the normalized ionic radii of the rare‐earth elements on the stability and the thermal expansion has been studied. It was demonstrated that the reduction of the normalized ionic radii of the rare‐earth results in reduced thermodynamic stability of the pyrochlore structure, but at the same time allows for obtaining higher values of the thermal expansion coefficient.