Performance and local structure evolution of NbMoTaWV entropy-stabilized oxide thin films with variable oxygen content

Entropy-stabilized refractory metal oxide thin films have great application prospects in many fields due to their good preparation performance, excellent thermal stability, high hardness and abrasion resistance, and adjustable conductivity. In present paper, a series of (NbMoTaWV)(100-x)O-x (x = 0-53.63) five-component entropy-stabilized oxide thin films were deposited on the single-crystal Si (100) substrates by radio frequency magnetron sputtering to study the effect of oxygen content on their performance and local structure. With increasing the oxygen content, the films gradually transform from body-centered-cubic solid solutions to the amorphous oxides. The hardness and modulus of the films obtain a maximum of 15.5 GPa and 215.6 GPa, respectively. The room temperature resistivity can be tuned in the range of 55-1.26 x 10(6) mu Omega.cm, and the trends of the resistivity-temperature behavior of the films have significant differences. Films with low oxygen contents show good resistivity stability in a wide temperature range. Simultaneously, the conductive mechanism gradually changes from the metallic type to amorphous oxide semiconductor type (a near TiO2 type ionic crystal type) as the oxygen content increases. The cluster-plus-glue-atom model has been introduced to interpret the composition of films, and the relationship between the variations of the local structure and strengthening (or conduction) mechanism is discussed in detail. Here, the performance of (NbMoTaWV)(100-x)O-x films can be modulated in a large range (covering conductors to semiconductors), which provides a broad prospect for the application of refractory high-entropy oxide films.