Accessing Novel Phase Space by The High Entropy Approach

Disorder and defects often dictate emergent phenomena in materials – such as electronic phase, magnetic ordering, and mechanical strength. Traditional thought pushes our understanding of phase order to rely on the idea of uniformity in materials, with disorder and defects resulting in lower ordering temperatures and prevention of long-range percolation. However, high entropy materials are challenging this understanding and disorder is emerging as a parameter which drives the local microstates into globally ordered behaviors. We demonstrate that this seemingly counterintuitive statement is not only true but that it simplifies the prediction of predominant functional phase in high entropy oxides. As a result, we design, grow, and characterize high entropy perovskite oxide films demonstrating the utility of this predictive materials approach.<br/><br/>We present these theoretical and experimental results on two classes of single crystal epitaxial films. Magnetism and charge disorder of the high entropy ABO₃ perovskite La(Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)O₃ is a representative case, demonstrating how a seemingly chaotic landscape of spin and charge disorder can yield an ordered state. Second, to explore electronic phase, we demonstrate realization of extreme <i>A</i>-site cation disorder in (Y_0.2La_0.2Nd_0.2Sm_0.2Gd_0.2)NiO₃, whose parent ternary oxides each have a large range of electronic (metal to insulator transition) and structural phase transition temperatures. These results suggest cation variance and disorder, such as that accessible only in high entropy oxides, can be a critical order parameter in the design of correlated oxides, and that this parameter can more broadly provide continuous tunability to emergent phenomena.