The classic auxetic perforated sheets with diamond-shaped voids reproducing the rotating-square topology are re-investigated and optimised via the incorporation of additional triangular voids at the edges of each diamond perforation. The scope is to make these systems lighter and render their pores more suitable for applications that require particular geometric features. Results show that the addition of such small- to medium-sized triangular voids did not have much effect on the extent of auxetic behaviour compared to the equivalent system having just diamond-shaped voids. This is rather remarkable given the very noticeable change in pore shape and size and the reduction in solid material and density. We also show that the exact magnitude of the Poisson's ratio may be fine-tuned through careful choice of various geometric parameters. All this broadens the potential of perforated auxetic systems for lightweight structural design and applications where specific pore geometries are required.
This article identifies and analyzes a new class of metamaterials that exhibit a previously unreported pseudo-bifurcation of on-axes Poisson's ratios. The metamaterials consist of rotating rhombic units, each composed of four triangular or trapezoidal subunits, which undergo either a fragmentation mechanism, whereby the subunits rotate relative to one another while preserving overall unit orientation, or a reconstitution mechanism in which all subunits rotate as a rigid body. Owing to their kinematic architecture, both metamaterials share common on-axes Poisson's ratios at two critical configurations: (i) in the reconstituted state and (ii) at the instant just prior to fragmentation. Beyond this point, under finite rotation of the subunits, the two on-axes Poisson's ratios bifurcate. These conditions correspond to unique geometric configurations that delimit the transition between common and bifurcated Poisson's ratios. The resulting metamaterials combine Poisson's ratio sign-switching, discontinuity, constancy under reconstitution, and pseudo-bifurcation under fragmentation-features not simultaneously present in earlier fragmentation-reconstitution (FR) metamaterials.
The reduction of the photoemission signal from the Shockley-type surface state of the Ag(110) surface upon the growth of one-dimensional single stranded Si nanoribbons (NRs) is modeled using a customized Poelsema-Comsa (P-C) geometric scattering model. The P-C model takes into account results from scanning tunneling microscopy data on the lengths of Si NRs, the release of Ag adatoms and the formation of narrow finger-like Ag terraces. The simulations show that the newly formed narrow Ag terraces have a negligible effect on the depopulation of the state, whereas the presence of Ag adatoms dominate the depopulation at higher coverage. We determine a depopulating effect of the Si NRs upon the Ag surface state in terms of a nanoscale patch area over which the Si NRs, and the Ag adatoms that they generate, subtract from the photoemission signal from the surface state. We find that the patch area is equivalent to each Si NR deactivating an orthogonal distance 0.6 nm either side of the NR. The work function of the surface is measured, revealing a linear increase in work function upon increasing Si NR coverage.
Rare-earth titanates RTiO3 exhibit a magnetic crossover from G-type antiferromagnetism (G-AFM) to ferromagnetism (FM) governed by the A-site ionic radius. We investigate the phase-boundary solid solution Gd0.5Sm0.5TiO3 using density functional theory (DFT) + U calculations to analyze competing magnetic orders. Our results identify the G-AFM configuration as the zero-temperature DFT ground state, separated from the metastable FM state by only 13.54 meV/Ti, indicating that 50% Sm substitution drives the system into the AFM regime. Conversely, A-type AFM and C-type AFM configurations are dynamically unstable. Analysis of local magnetic moments reveals robust rare-earth ferrimagnetism but highly sensitive Ti moments (0.15-0.64 ) arising from exchange frustration. The energetic proximity of the G-AFM and FM phases suggests that field-induced metamagnetic transitions are achievable at accessible magnetic fields (5-10 T). Thus, the Gd1 -xSmxTiO3 series offers a tunable platform for optimizing magnetocaloric effects for cryogenic cooling applications.
During bonding and service processes, the remarkable anisotropic behavior of hexagonal Cu6Sn5 (eta-Cu6Sn5) intermetallic compound (IMC) in Sn-based solder/Cu joints may result in abnormal IMC growth and subsequent failure of the solder joints. In this work, the crystalline structure, elastic properties, fracture toughness and electronic features of hexagonal eta-Cu6Sn5 with Co atoms doped at the various unfilled Cu2 sites were systematically analyzed using first-principles methods. The Young's and bulk modulus of the Co-free eta-Cu6Sn5 and its doping systems were characterized by three-dimensional plane projections constructions, and the Young's and shear modulus were characterized by two-dimensional plane projections. The results revealed that doping Co atoms can change the elastic anisotropy and shear resistance of eta-Cu6Sn5. Doping Co into most sites can enhance the fracture toughness of eta-Cu6Sn5 to varying degrees. Electronic structure analyses demonstrated that the doping of Co changed both the electronic configuration and structural stability of eta-Cu6Sn5. Specifically, hybridization between Co-d and Sn-p orbitals was observed, which results in a higher peak intensity near -1.51 eV. Notably, Co-doping at particular sites led to significant improvement in the structural stability of eta-Cu6Sn5.
