High-entropy oxide thin films based on Al–Cr–Nb–Ta–Ti

Abstract Single-phase crystalline (Al,Cr,Nb,Ta,Ti)O2 high-entropy oxide thin films were synthesized at 400 °C by reactive magnetron sputtering of an equimolar Al–Cr–Nb–Ta–Ti-compound target. These show similar chemistry as well as the same rutile structure, even when varying the relative oxygen flow-rate ratio (fO2) during deposition over a wide range. Upon increasing fO2 from 30 to 80%, their hardness increases from 22 to 24 GPa and their indentation moduli increased from 380 to 410 GPa. The materials stayed single-phase crystalline with the rutile structure during vacuum annealing up to 1200 °C, only their orientation changed from random-like to highly 101-textured.