High Entropy Oxide Relaxor Ferroelectrics.

Relaxor ferroelectrics are important in technological applications due to strong electromechanical response, energy storage capacity, electrocaloric effect, and pyroelectric energy conversion properties. Current efforts to discover and design materials in this class generally rely on substitutional doping as slight changes to local compositional order can significantly affect the Curie temperature, morphotropic phase boundary, and electromechanical responses. In this work, we demonstrate that moving to the strong limit of compositional complexity in an O perovskite allows stabilization of relaxor responses that do not rely on a single narrow phase transition region.

Designing Magnetism in High Entropy Oxides.

In magnetic systems, spin and exchange disorder can provide access to quantum criticality, frustration, and spin dynamics, but broad tunability of these responses and a deeper understanding of strong limit disorder are lacking. Here, it is demonstrated that high entropy oxides present a previously unexplored route to designing materials in which the presence of strong local compositional disorder may be exploited to generate tunable magnetic behaviors-from macroscopically ordered states to frustration-driven dynamic spin interactions. Single-crystal La(Cr Mn Fe Co Ni )O films are used as a model system hosting a magnetic sublattice with a high degree of microstate disorder in the form of site-to-site spin and exchange type inhomogeneity.

Magnetic Texture in Insulating Single Crystal High Entropy Oxide Spinel Films.

Magnetic insulators are important materials for a range of next-generation memory and spintronic applications. Structural constraints in this class of devices generally require a clean heterointerface that allows effective magnetic coupling between the insulating layer and the conducting layer. However, there are relatively few examples of magnetic insulators that can be synthesized with surface qualities that would allow these smooth interfaces and precisely tuned interfacial magnetic exchange coupling, which might be applicable at room temperature.

Applying Configurational Complexity to the 2D Ruddlesden-Popper Crystal Structure.

The layered Ruddlesden-Popper crystal structure can host a broad range of functionally important behaviors. Here we establish extraordinary configurational disorder in a layered Ruddlesden-Popper (RP) structure using entropy stabilization assisted synthesis. A protype CuO RP cuprate oxide with five cations on the -site sublattice is designed and fabricated into epitaxial single crystal films using pulsed laser deposition.

Temperature dependence of elastic and plastic deformation behavior of a refractory high-entropy alloy.

Single-phase solid-solution refractory high-entropy alloys (HEAs) show remarkable mechanical properties, such as their high yield strength and substantial softening resistance at elevated temperatures. Hence, the in-depth study of the deformation behavior for body-centered cubic (BCC) refractory HEAs is a critical issue to explore the uncovered/unique deformation mechanisms. We have investigated the elastic and plastic deformation behaviors of a single BCC NbTaTiV refractory HEA at elevated temperatures using integrated experimental efforts and theoretical calculations.

Optomechanical Effects Occurring in a Hybrid Metal-Halide Perovskite Single Crystal Based on Photoinduced Resonant Ultrasound Spectroscopy.

This letter reports optomechanical effects occurring in a hybrid metal-halide perovskite single crystal (MAPbBr) based on resonant ultrasound spectroscopy (RUS) measurements under continuous wave (CW) laser illumination. The optomechanical effects are a new phenomenon in hybrid perovskite single crystals where the elastic constant of a single crystal is measured by RUS probed under varying excitation conditions. Our studies show that applying a CW laser (405 nm) to the single-crystal face shifts the RUS peaks to higher frequencies by about 1-4% in the perovskite single crystal at room temperature.