As a new class of multi-principal component oxides with high chemical disorder, high-entropy oxides (HEOs) have attracted much attention. The stability and tunability of their structure and properties are of great interest and importance, but remain unclear. By using in situ synchrotron radiation X-ray diffraction, Raman spectroscopy, ultraviolet-visible absorption spectroscopy, and ex situ high-resolution transmission electron microscopy, here we show the existence of lattice distortion in the crystalline (Ce 0.2 La 0.2 Pr 0.2 Sm 0.2 Y 0.2 )O 2−δ HEO according to the deviation of bond angles from the ideal values, and discover a pressureinduced continuous tuning of lattice distortion (bond angles) and band gap. As continuous bending of bond angles, pressure eventually induces breakdown of the long-range connectivity of lattice and causes amorphization. The amorphous state can be partially recovered upon decompression, forming glass-nanoceramic composite HEO. These results reveal the unexpected flexibility of the structure and properties of HEOs, which could promote the fundamental understanding and applications of HEOs.

The recently discovered pressure-induced polymorphic transitions (PIPT) in high-entropy alloys (HEAs) have opened an avenue towards understanding the phase stability and achieving atomic structural tuning of HEAs. So far, whether there is any PIPT in the body-centered cubic (bcc) HEAs remains unclear. Here, we studied an ordered bcc-structured (B2 phase) AlCoCrFeNi HEA using in situ synchrotron radiation X-ray diffraction (XRD) up to 42 GPa and ex situ transmission electron microscopy, a PIPT to a likely-distorted phase was observed. These results highlight the effect of the lattice distortion on the stability of HEAs and extend the polymorphism into ordered bcc-structured HEAs.

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