Ten different high-entropy rare-earth zirconates with the general formula of A 2 Zr 2 O 7 were synthesized using reverse coprecipitation. Thereby, five cations were mixed on the A sublattice, and their composition was varied systematically regarding cation size to vary the cationic radius ratio r A /r B and the atomic size difference δ A . Phase and chemical composition as well as morphology of the synthesized materials were examined by X-ray diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, and electron probe microanalysis. Additionally, their phase stability was investigated using high-temperature XRD and differential scanning calorimetry.Single-phase materials were obtained when δ A was below 4.5%. This threshold value was determined and verified using additional data taken from literature.The single-phase compositions formed pyrochlore or defect fluorite structure depending on their r A /r B with a threshold value of 1.46 being the same as for binary zirconates. Furthermore, the single-phase compositions remained stable up to high temperatures.

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