Effect of processing route on the crystal structure and physical properties of bixbyite high-entropy oxides

•High-entropy rare earth oxides (HE-REOs) with the form (Y-La-Ce-Nd-Gd)2O3+β were synthesized.•Both mechanochemical (ball milling) and chemical (sol-gel) methods were employed.•Compositional uniformity of as-synthesized powders were in the following order: sol-gel>wet milling>dry milling.•The synthesized HE-REOs exhibited very high phase stability.