Exploring the tetragonal distortion in Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O high entropy oxide: a dark field X-ray microscopy investigation

High entropy oxides (HEOs) are a recently reported classe of materials characterized by a particularly large value of configurational entropy. They can be obtained by mixing at least five different oxides in equimolar ration, resulting into a single-phase structure. The pioneering system is Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O, having a rock salt structure. While this material is characterized by the cubic structure at room temperature, it undergoes a signifcant structural change, compatible to an incipient cubic-to-tetragonal phase transition, in a temperature range comprised between 250 and ca. 500 °C. The aim of this proposal is to perform dark field X-ray microscopy (DFXM) to investigate these distortions, by probing local orientation and strain variations within individual grains. We expect that this, coupled to results from a previous XRD experiment, will demonstrate the existence and stabilization of single-phase high- and medium-entropy oxides in the tetragonal phase.