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Hydrogen-doped perovskites can be reconfigured by electrical pulses to take on all essential functions necessary for artificial intelligence hardware. 

The bulk piezoelectric response, as measured by the piezoelectric modulus tensor ( d ), is determined by a combination of charge redistribution due to strain and the amount of strain produced by the application of stress (stiffness). Motivated by the notion that less stiff materials could exhibit large piezoelectric responses, herein, we investigate the piezoelectric modulus of van der Waals (vdW) layered materials using first-principles calculations. From a pool of 869 known binary and ternary quasi-2D layered materials, we have identified 135 non-centrosymmetric crystals of which 51 are found to have piezoelectric modulus tensor ( d ) components larger than the longitudinal piezoelectric modulus of AlN, a commonly used piezoelectric material for resonators. We have also identified three materials with d components larger than that of PbTiO 3 , which is among the materials with the largest known piezoelectric modulus. None of the identified materials have previously been considered for piezoelectric applications. Furthermore, we find that large d components are always coupled to the shear or axial deformations of the vdW gap between the layers and are indeed enabled by the weak inter-layer interactions. 

In this work, we expand the set of known layered compounds to include ionic layered materials, which are well known for superconducting, thermoelectric, and battery applications. Focusing on known ternary compounds from the ICSD, we screen for ionic layered structures by expanding upon our previously developed algorithm for identification of van der Waals (vdW) layered structures, thus identifying over 1500 ionic layered compounds. Since vdW layered structures can be chemically mutated to form ionic layered structures, we have developed a methodology to structurally link binary vdW to ternary ionic layered materials. We perform an in-depth analysis of similarities and differences between these two classes of layered systems and assess the interplay between layer geometry and bond strength with a study of the elastic anisotropy. We observe a rich variety of anisotropic behavior in which the layering direction alone is not a simple predictor of elastic anisotropy. Our results enable discovery of new layered materials through intercalation or de-intercalation of vdW or ionic layered systems, respectively, as well as lay the groundwork for studies of anisotropic transport phenomena such as sound propagation or lattice thermal conductivity.