Negative Linear Compressibility and Auxeticity in Boron Arsenate

Abstract

A novel mechanism is identified leading to negative linear compressibility (NLC) in boron arsenate which is shown to arise from deformations in the framework tetrahedra rather than more conspicuous tetrahedral rotations. Instead, such rotations, which manifest as "rotating squares" when viewed down the c direction, are found to result in negative Poisson's ratio (NPR) in the (001) plane, which in turn augments the compressibility, a phenomenon that should be applicable to other auxetic materials. It is hypothesized that the generic NLC and NPR mechanisms identified here, as well as the augmented compressibility due to auxeticity should also feature in materials and metamaterials with similar characteristics. systems such as -cristobalite isostructural crystals with an I42d or I4 symmetry. Similarly, NLC is commonly associated with wine-rack motifs [37,39] or other mechanisms. [39] Negative compressibility and negative Poisson's ratio have also long been known in the vicinity of phase transformations. [39,47] The present work will study the effect of pressure, uniaxial loading, and shearing on boron arsenate, in an attempt to unearth the mechanisms which lead to NLC and NPR in this stable member of I4 space group, through the quantitative measurement of the molecular level deformations. This will help the understanding of the mechanisms leading to such anomalous "negative mechanical behavior" in crystals and in the process pave the way to the design of novel metamaterials inspired from it.

Structure Dependence of Poisson’s Ratio in Cesium Silicate and Borate Glasses

“…The deformation behavior of isotropic glasses, even beyond the elastic limit, has been proposed to be closely related to Poisson's ratio (ν), which is defined as the negative ratio of the transverse strain relative to the longitudinal strain in the elastic loading direction. For example, glasses with low ν are generally more prone to undergo a high degree of densification during indentation [5]-we here note that homogeneous oxide glasses only exhibit positive values of ν, although negative ν is possible in other material families [6]. As such, ν is also closely related to the atomic packing density (C g ) [7], with compressible silica having a low C g and thus a low ν.…”

On the Design of Multimaterial Honeycombs and Structures with T‐Shaped Joints Having Tunable Thermal and Compressibility Properties

“…Such systems should not be confused with what is normally represented in modeling and experimental work related to crystalline materials (e.g., ref. [56]) where the pressure is only exerted on the outer surface of the materials (Figure 5b), which in simulations is typically represented by the boundaries of the unit cells. In other words, the way that the systems are modeled is analogous to an open-cell foam material being inserted in a fluid on which pressure is exerted.…”

“…This led to various studies in the last decades which were focused on the design and investigation of honeycombs specifically engineered to exhibit anomalous or superior thermomechanical properties, such as a negative Poisson's ratio (auxetic behavior) . Given the advantages of honeycombs over nonporous solids, when put in the context of the developments which are being made on “negative thermomechanical properties,” it is not surprising that research in the field of “negative honeycombs” is still the subject of extensive research …”

An Auxetic Metamaterial with Tunable Positive to Negative Hygrothermal Expansion by means of Counter‐Rotating Crosses

“…Likewise, precision microstructural design permits the development of accurately controlled thermal strain, as demonstrated by the NTE microstructure of Vandeperre and Clegg, [ 65 ] which is of great practical importance, including in the design of optical fibers. [ 66 ] Similarly, a novel mechanism has been identified by Grima‐Cornish et al [ 67 ] in boron arsenate, which arises from deformations in the framework tetrahedra rather than tetrahedral rotations, to manifest negative linear compressibility (NLC).…”